1.
SN 1054
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SN1054 is a supernova that was first observed on 4 July 1054, and remained visible for around two years. The event was recorded in contemporary Chinese astronomy, and references to it are found in a later Japanese document. The remnant of SN1054, which consists of debris ejected during the explosion, is known as the Crab Nebula and it is located in the sky near the star Zeta Tauri. The core of the star formed a pulsar, called the Crab Pulsar. The nebula and the pulsar that it contains are some of the most studied astronomical objects outside the Solar System and it is one of the few Galactic supernovae where the date of the explosion is well known. The two objects are the most luminous in their respective categories, for these reasons, and because of the important role it has repeatedly played in the modern era, SN1054 is the best known supernova in the history of astronomy. When the French astronomer Charles Messier watched for the return of Halleys Comet in 1758, he confused the nebula for the comet, due to this error, he created his catalogue of non-cometary nebulous objects, the Messier Catalogue, to avoid such mistakes in the future. The nebula is catalogued as the first Messier object, or M1, the Crab Nebula was identified as the supernova remnant of SN1054 between 1921 and 1942, at first speculatively, with some plausibility by 1939, and beyond reasonable doubt by Jan Oort in 1942. In 1921, Carl Otto Lampland was the first to announce that he had changes in the structure of the Crab Nebula. This announcement occurred at a time when the nature of the nebulas in the sky was completely unknown and their nature, size and distance were subject to debate. Lamplands comments were confirmed some weeks later by John Charles Duncan, the points were moving away from the centre, and did so faster as they got further from it. Also in 1921, Knut Lundmark compiled the data for the guest stars mentioned in the Chinese chronicles known in the West. Lundmark gives a list of 60 suspected novae, then the term for a stellar explosion. The nova of 1054, already mentioned by the Biots in 1843, is part of the list. In 1928, Edwin Hubble was the first to note that the aspect of the Crab Nebula. Hubble therefore deduced, correctly, that this cloud was the remains of the explosion which was observed by Chinese astronomers, hubbles comment remained relatively unknown as the physical phenomenon of the explosion was not known at the time. This was under the assumption that the velocities of expansion along the line of sight, based on the reference to the brightness of the star which featured in the first documents discovered in 1934, he deduced that it was a supernova rather than a nova. This deduction was subsequently refined, which pushed Mayall and Jan Oort in 1942 to analyse historic accounts relating to the guest star more closely, other historical supernovae of which there are written accounts which precede the invention of the telescope are however established with certitude
2.
Crab Nebula
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The Crab Nebula is a supernova remnant in the constellation of Taurus. The now-current name is due to William Parsons, 3rd Earl of Rosse, corresponding to a bright supernova recorded by Chinese astronomers in 1054, the nebula was observed later by English astronomer John Bevis in 1731. The nebula was the first astronomical object identified with a supernova explosion. At an apparent magnitude of 8.4, comparable to that of Saturns moon Titan, it is not visible to the naked eye, the nebula lies in the Perseus Arm of the Milky Way galaxy, at a distance of about 2.0 kiloparsecs from Earth. It has a diameter of 3.4 parsecs, corresponding to an apparent diameter of some 7 arcminutes, and is expanding at a rate of about 1,500 kilometres per second, or 0. 5% of the speed of light. At the center of the lies the Crab Pulsar, a neutron star 28–30 kilometres across with a spin rate of 30.2 times per second. At X-ray and gamma ray energies above 30 keV, the Crab Nebula is generally the strongest persistent source in the sky, the nebulas radiation allows for the detailed studying of celestial bodies that occult it. The inner part of the nebula is a much smaller pulsar wind nebula that appears as a shell surrounding the pulsar, for the Crab Nebula, the divisions are superficial but remain meaningful to researchers and their lines of study. Modern understanding that the Crab Nebula was created by a supernova dates to 1921 and this eventually led to the conclusion that the creation of the Crab Nebula corresponds to the bright SN1054 supernova recorded by Chinese astronomers in AD1054. There is also a 13th-century Japanese reference to this guest star in Meigetsuki, the Crab Nebula was first identified in 1731 by John Bevis. The nebula was independently rediscovered in 1758 by Charles Messier as he was observing a bright comet and it is in searching in vain for the comet that Charles Messier found the Crab nebula, which he at first thought to be Halleys comet. After some observation, noticing that the object that he was observing was not moving across the sky, Messier then realised the usefulness of compiling a catalogue of celestial objects of a cloudy nature, but fixed in the sky, to avoid incorrectly cataloguing them as comets. After several observations, he concluded that it was composed of a group of stars. The 3rd Earl of Rosse observed the nebula at Birr Castle in 1844 using a 36-inch telescope and he observed it again later, in 1848, using a 72-inch telescope and could not confirm the supposed resemblance, but the name stuck nevertheless. In 1913, when Vesto Slipher registered his spectroscopy study of the sky, in the early twentieth century, the analysis of early photographs of the nebula taken several years apart revealed that it was expanding. Tracing the expansion back revealed that the nebula must have become visible on Earth about 900 years ago, historical records revealed that a new star bright enough to be seen in the daytime had been recorded in the same part of the sky by Chinese astronomers in 1054. Changes in the cloud, suggesting its small extent, were discovered by Carl Lampland in 1921 and that same year, John Charles Duncan demonstrated that the remnant is expanding, while Knut Lundmark noted its proximity to the guest star of 1054.5 by July. The supernova was visible to the eye for about two years after its first observation
3.
Star
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A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun, many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, indeed, most are invisible from Earth even through the most powerful telescopes. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the stars lifetime, near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity, and many properties of a star by observing its motion through space, its luminosity. The total mass of a star is the factor that determines its evolution. Other characteristics of a star, including diameter and temperature, change over its life, while the environment affects its rotation. A plot of the temperature of stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram. Plotting a particular star on that allows the age and evolutionary state of that star to be determined. A stars life begins with the collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, the remainder of the stars interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The stars internal pressure prevents it from collapsing further under its own gravity, a star with mass greater than 0.4 times the Suns will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements at the core or in shells around the core, as the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. Meanwhile, the core becomes a remnant, a white dwarf. Binary and multi-star systems consist of two or more stars that are bound and generally move around each other in stable orbits. When two such stars have a close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, historically, stars have been important to civilizations throughout the world
4.
Supernova
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This causes the sudden appearance of a new bright star, before slowly fading from sight over several weeks or months. Supernovae are more energetic than novae, in Latin, nova means new, referring astronomically to what appears to be a temporary new bright star. Adding the prefix super- distinguishes supernovae from ordinary novae, which are far less luminous, the word supernova was coined by Walter Baade and Fritz Zwicky in 1931. It is pronounced /ˌsuːpərnoʊvə/ with the plural supernovae /ˌsuːpərnoʊviː/ or supernovas, only three Milky Way naked-eye supernova events have been observed during the last thousand years, though many have been seen in other galaxies using telescopes. The most recent directly observed supernova in the Milky Way was Keplers Supernova in 1604, Supernovae may expel much, if not all, of the material away from a star, at velocities up to 30,000 km/s or 10% of the speed of light. This drives an expanding and fast-moving shock wave into the interstellar medium, and in turn, sweeping up an expanding shell of gas and dust. Supernovae create, fuse and eject the bulk of the chemical elements produced by nucleosynthesis, Supernovae play a significant role in enriching the interstellar medium with the heavier atomic mass chemical elements. Furthermore, the shock waves from supernovae can trigger the formation of new stars. Supernova remnants are expected to accelerate a large fraction of primary cosmic rays. They are also potentially strong galactic sources of gravitational waves, in the second case, the core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy as a supernova. While some observed supernovae are more complex than these two simplified theories, the astrophysical collapse mechanics have been established and accepted by most astronomers for some time, in Latin, Nova means new, referring astronomically to what appears to be a temporary new bright star. Adding the prefix super- distinguishes supernovae from ordinary novae, which are far less luminous, the word supernova was coined by Walter Baade and Fritz Zwicky in 1931. It is pronounced /ˌsuːpərnoʊvə/ with the plural supernovae /ˌsuːpərnoʊviː/ or supernovas, the earliest recorded supernova, SN185, was viewed by Chinese astronomers in 185 AD. The brightest recorded supernova was SN1006, which occurred in 1006 AD and was described in detail by Chinese, the widely observed supernova SN1054 produced the Crab Nebula. Johannes Kepler began observing SN1604 at its peak on October 17,1604 and it was the second supernova to be observed in a generation. There is some evidence that the youngest galactic supernova, G1. 9+0.3, occurred in the late 19th century, neither supernova was noted at the time. In the case of G1. 9+0.3, high extinction along the plane of the galaxy could have dimmed the event sufficiently to go unnoticed, the situation for Cassiopeia A is less clear. Infrared light echos have been detected showing that it was a type IIb supernova and was not in a region of especially high extinction, before the development of the telescope, there have only been five supernovae seen in the last millennium
5.
Shock wave
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In physics, a shock wave, or shock, is a type of propagating disturbance. When a wave moves faster than the speed of sound in a fluid it is a shock wave. In supersonic flows, expansion is achieved through an expansion fan also known as a Prandtl-Meyer expansion fan, unlike solitons, the energy of a shock wave dissipates relatively quickly with distance. Also, the accompanying expansion wave approaches and eventually merges with the shock wave, when a shock wave passes through matter, energy is preserved but entropy increases. Shock waves can be, Normal, at 90° to the shock mediums flow direction, oblique, at an angle to the direction of flow. Bow, Occurs upstream of the front of a blunt object when the flow velocity exceeds Mach 1. Some other terms Shock Front, The boundary over which the physical conditions undergo a change because of a shock wave. Contact Front, in a wave caused by a driver gas. The Contact Front trails the Shock Front, when an object moves faster than the information about it can propagate into the surrounding fluid, fluid near the disturbance cannot react or get out of the way before the disturbance arrives. In a shock wave the properties of the fluid change almost instantaneously, measurements of the thickness of shock waves in air have resulted in values around 200 nm, which is on the same order of magnitude as the mean free gas molecule path. In reference to the continuum, this implies the shock wave can be treated as either a line or a plane if the field is two-dimensional or three-dimensional. Shock waves are formed when a pressure front moves at supersonic speeds, Shock waves are not conventional sound waves, a shock wave takes the form of a very sharp change in the gas properties. Shock waves in air are heard as a crack or snap noise. Over longer distances, a wave can change from a nonlinear wave into a linear wave, degenerating into a conventional sound wave as it heats the air. The sound wave is heard as the familiar thud or thump of a sonic boom, the shock wave is one of several different ways in which a gas in a supersonic flow can be compressed. Some other methods are isentropic compressions, including Prandtl-Meyer compressions, the method of compression of a gas results in different temperatures and densities for a given pressure ratio which can be analytically calculated for a non-reacting gas. A shock wave compression results in a loss of pressure, meaning that it is a less efficient method of compressing gases for some purposes. The appearance of pressure-drag on supersonic aircraft is due to the effect of shock compression on the flow
6.
Neutron star
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A neutron star is the collapsed core of a large star. Neutron stars are the smallest and densest stars known to exist, though neutron stars typically have a radius on the order of 10 km, they can have masses of about twice that of the Sun. They result from the explosion of a massive star, combined with gravitational collapse. They are supported against further collapse by neutron degeneracy pressure, a described by the Pauli exclusion principle. If the remnant has too great a density, something which occurs in excess of a limit of the size of neutron stars at 2–3 solar masses. Neutron stars that can be observed are very hot and typically have a temperature around 6×105 K. They are so dense that a normal-sized matchbox containing neutron-star material would have a mass of approximately 3 billion tonnes and their magnetic fields are between 108 and 1015 times as strong as that of the Earth. The gravitational field at the stars surface is about 2×1011 times that of the Earth. As the stars core collapses, its rotation rate increases as a result of conservation of angular momentum, some neutron stars emit beams of electromagnetic radiation that make them detectable as pulsars. Indeed, the discovery of pulsars in 1967 was the first observational suggestion that stars exist. The radiation from pulsars is thought to be emitted from regions near their magnetic poles. The fastest-spinning neutron star known is PSR J1748-2446ad, rotating at a rate of 716 times a second or 43,000 revolutions per minute, giving a linear speed at the surface on the order of 0.24 c. There are thought to be around 100 million neutron stars in the Milky Way, however, most are old and cold, and neutron stars can only be easily detected in certain instances, such as if they are a pulsar or part of a binary system. Soft gamma repeaters are conjectured to be a type of neutron star with strong magnetic fields, known as magnetars, or alternatively. Additionally, such accretion can recycle old pulsars and potentially cause them to mass and spin-up to very fast rotation rates. The merger of binary stars may be the source of short-duration gamma-ray bursts and are likely strong sources of gravitational waves. Any main-sequence star with a mass of above 8 times the mass of the sun has the potential to produce a neutron star. As the star evolves away from the sequence, subsequent nuclear burning produces an iron-rich core
7.
Black hole
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A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. The theory of relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon, although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. In many ways a black hole acts like a black body. Moreover, quantum theory in curved spacetime predicts that event horizons emit Hawking radiation. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. Black holes were considered a mathematical curiosity, it was during the 1960s that theoretical work showed they were a generic prediction of general relativity. The discovery of neutron stars sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality, black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings, by absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is general consensus that supermassive black holes exist in the centers of most galaxies, despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Matter that falls onto a black hole can form an accretion disk heated by friction. If there are other stars orbiting a black hole, their orbits can be used to determine the black holes mass, such observations can be used to exclude possible alternatives such as neutron stars.3 million solar masses. On 15 June 2016, a detection of a gravitational wave event from colliding black holes was announced. The idea of a body so massive that light could not escape was briefly proposed by astronomical pioneer John Michell in a letter published in 1783-4. Michell correctly noted that such supermassive but non-radiating bodies might be detectable through their effects on nearby visible bodies. In 1915, Albert Einstein developed his theory of general relativity, only a few months later, Karl Schwarzschild found a solution to the Einstein field equations, which describes the gravitational field of a point mass and a spherical mass. A few months after Schwarzschild, Johannes Droste, a student of Hendrik Lorentz, independently gave the solution for the point mass. This solution had a peculiar behaviour at what is now called the Schwarzschild radius, the nature of this surface was not quite understood at the time
8.
White dwarf
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A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense, its mass is comparable to that of the Sun, a white dwarfs faint luminosity comes from the emission of stored thermal energy, no fusion takes place in a white dwarf wherein mass is converted to energy. The nearest known white dwarf is Sirius B, at 8.6 light years, there are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910, the name white dwarf was coined by Willem Luyten in 1922. The universe has not existed long enough to experience a white dwarf releasing all of its energy as it will take many billions of years. If a red giant has insufficient mass to generate the temperatures, around 1 billion K, required to fuse carbon. After such a star sheds its outer layers and forms a planetary nebula, it will leave behind a core, usually, white dwarfs are composed of carbon and oxygen. If the mass of the progenitor is between 8 and 10.5 solar masses, the temperature will be sufficient to fuse carbon but not neon. Stars of very low mass will not be able to fuse helium, hence, the material in a white dwarf no longer undergoes fusion reactions, so the star has no source of energy. As a result, it support itself by the heat generated by fusion against gravitational collapse. A carbon-oxygen white dwarf that approaches this limit, typically by mass transfer from a companion star. A white dwarf is very hot when it forms, but because it has no source of energy, it will gradually radiate its energy and this means that its radiation, which initially has a high color temperature, will lessen and redden with time. Over a very time, a white dwarf will cool. The stars low temperature means it will no longer emit significant heat or light, and it will become a cold black dwarf. Because the length of time it takes for a dwarf to reach this state is calculated to be longer than the current age of the universe. The oldest white dwarfs still radiate at temperatures of a few thousand kelvins, the pair 40 Eridani B/C was discovered by William Herschel on 31 January 1783, p.73 it was again observed by Friedrich Georg Wilhelm Struve in 1825 and by Otto Wilhelm von Struve in 1851. In 1910, Henry Norris Russell, Edward Charles Pickering and Williamina Fleming discovered that, despite being a dim star,40 Eridani B was of spectral type A, or white. In 1939, Russell looked back on the discovery, p.1 I was visiting my friend and generous benefactor and this piece of apparently routine work proved very fruitful—it led to the discovery that all the stars of very faint absolute magnitude were of spectral class M
9.
Accretion (astrophysics)
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In astrophysics, accretion is the accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, in an accretion disk. Most astronomical objects, such as galaxies, stars, and planets, are formed by accretion processes, the idea proposed in the 19th century that Earth and the other terrestrial planets formed from meteoric material was developed in a quantitative way in 1969 by Viktor Safronov. He calculated, in detail, the different stages of planet formation. Since then, the theory has been developed using intensive numerical simulations to study planetesimal accumulation. Stars form by the collapse of interstellar gas. Prior to collapse, this gas is mostly in the form of molecular clouds, as the cloud collapses, losing potential energy, it heats up, gaining kinetic energy, and the conservation of angular momentum ensures that the cloud forms a flatted disk—the accretion disk. A few hundred years after the Big Bang, the Universe cooled to the point where atoms could form. As the Universe continued to expand and cool, the atoms lost enough kinetic energy, as further accretion occurred, galaxies formed. Galaxies grow through mergers and smooth gas accretion, accretion also occurs inside galaxies, forming stars. Stars are thought to form inside giant clouds of cold molecular hydrogen—giant molecular clouds of roughly 300,000 M☉ and 65 light-years in diameter, over millions of years, giant molecular clouds are prone to collapse and fragmentation. These fragments then form small, dense cores, which in turn collapse into stars, the cores range in mass from a fraction to several times that of the Sun and are called protostellar nebulae. They possess diameters of 2, 000–20,000 astronomical units, compare it with the particle number density of the air at the sea level—2. 8×1019/cm3. The initial collapse of a solar-mass protostellar nebula takes around 100,000 years, every nebula begins with a certain amount of angular momentum. This core forms the seed of what will become a star, as the collapse continues, conservation of angular momentum dictates that the rotation of the infalling envelope accelerates, which eventually forms a disk. Around this time the protostar begins to fuse deuterium, if the protostar is sufficiently massive, hydrogen fusion follows. Otherwise, if its mass is too low, the object becomes a brown dwarf and this birth of a new star occurs approximately 100,000 years after the collapse begins. Objects at this stage are known as Class I protostars, which are also called young T Tauri stars, evolved protostars, or young stellar objects. By this time, the star has already accreted much of its mass
10.
Supersonic speed
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Supersonic travel is a rate of travel of an object that exceeds the speed of sound. For objects traveling in dry air of a temperature of 20 °C at sea level, speeds greater than five times the speed of sound are often referred to as hypersonic. Flights during which some parts of the air surrounding an object, such as the ends of rotor blades. This occurs typically somewhere between Mach 0.8 and Mach 1.23, sounds are traveling vibrations in the form of pressure waves in an elastic medium. In gases, sound travels longitudinally at different speeds, mostly depending on the mass and temperature of the gas. Since air temperature and composition varies significantly with altitude, Mach numbers for aircraft may change despite a constant travel speed, in water at room temperature supersonic speed can be considered as any speed greater than 1,440 m/s. In solids, sound waves can be polarized longitudinally or transversely and have higher velocities. Supersonic fracture is crack motion faster than the speed of sound in a brittle material, at the beginning of the 20th century, the term supersonic was used as an adjective to describe sound whose frequency is above the range of normal human hearing. The modern term for this meaning is ultrasonic, the tip of a bullwhip is thought to be the first man-made object to break the sound barrier, resulting in the telltale crack. The wave motion traveling through the bullwhip is what makes it capable of achieving supersonic speeds, most modern fighter aircraft are supersonic aircraft, but there have been supersonic passenger aircraft, namely Concorde and the Tupolev Tu-144. Both these passenger aircraft and some modern fighters are also capable of supercruise, since Concordes final retirement flight on November 26,2003, there are no supersonic passenger aircraft left in service. Some large bombers, such as the Tupolev Tu-160 and Rockwell B-1 Lancer are also supersonic-capable, most modern firearm bullets are supersonic, with rifle projectiles often travelling at speeds approaching and in some cases well exceeding Mach 3. Most spacecraft, most notably the Space Shuttle are supersonic at least during portions of their reentry, during ascent, launch vehicles generally avoid going supersonic below 30 km to reduce air drag. Note that the speed of sound decreases somewhat with altitude, due to lower temperatures found there, at even higher altitudes the temperature starts increasing, with the corresponding increase in the speed of sound. When an inflated balloon is burst, the pieces of latex contracts at a supersonic speed. Supersonic aerodynamics is simpler than subsonic aerodynamics because the airsheets at different points along the plane often cant affect each other, Supersonic jets and rocket vehicles require several times greater thrust to push through the extra aerodynamic drag experienced within the transonic region. Designers use the Supersonic area rule and the Whitcomb area rule to minimize changes in size. However, in applications, a supersonic aircraft will have to operate stably in both subsonic and supersonic profiles, hence aerodynamic design is more complex
11.
Mach number
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In fluid dynamics, the Mach number is a dimensionless quantity representing the ratio of flow velocity past a boundary to the local speed of sound. M = u c, where, M is the Mach number, u is the flow velocity with respect to the boundaries. By definition, Mach 1 is equal to the speed of sound, Mach 0.65 is 65% of the speed of sound, and Mach 1.35 is 35% faster than the speed of sound. The local speed of sound, and thereby the Mach number, depends on the condition of the surrounding medium, the Mach number is primarily used to determine the approximation with which a flow can be treated as an incompressible flow. The medium can be a gas or a liquid, the boundary can be the boundary of an object immersed in the medium, or of a channel such as a nozzle, diffusers or wind tunnels channeling the medium. As the Mach number is defined as the ratio of two speeds, it is a dimensionless number, if M <0. 2–0.3 and the flow is quasi-steady and isothermal, compressibility effects will be small and simplified incompressible flow equations can be used. The Mach number is named after Austrian physicist and philosopher Ernst Mach, as the Mach number is a dimensionless quantity rather than a unit of measure, with Mach, the number comes after the unit, the second Mach number is Mach 2 instead of 2 Mach. This is somewhat reminiscent of the modern ocean sounding unit mark, which was also unit-first. In the decade preceding faster-than-sound human flight, aeronautical engineers referred to the speed of sound as Machs number, never Mach 1, Mach number is useful because the fluid behaves in a similar manner at a given Mach number, regardless of other variables. As modeled in the International Standard Atmosphere, dry air at sea level, standard temperature of 15 °C. For example, the atmosphere model lapses temperature to −56.5 °C at 11,000 meters altitude. In the following table, the regimes or ranges of Mach values are referred to, generally, NASA defines high hypersonic as any Mach number from 10 to 25, and re-entry speeds as anything greater than Mach 25. Aircraft operating in this include the Space Shuttle and various space planes in development. Flight can be classified in six categories, For comparison. At transonic speeds, the field around the object includes both sub- and supersonic parts. The transonic period begins when first zones of M >1 flow appear around the object, in case of an airfoil, this typically happens above the wing. Supersonic flow can decelerate back to only in a normal shock. As the speed increases, the zone of M >1 flow increases towards both leading and trailing edges
12.
Plasma (physics)
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Plasma is one of the four fundamental states of matter, the others being solid, liquid, and gas. Yet unlike these three states of matter, plasma does not naturally exist on the Earth under normal surface conditions, the term was first introduced by chemist Irving Langmuir in the 1920s. However, true plasma production is from the separation of these ions and electrons that produces an electric field. Based on the environmental temperature and density either partially ionised or fully ionised forms of plasma may be produced. The positive charge in ions is achieved by stripping away electrons from atomic nuclei, the number of electrons removed is related to either the increase in temperature or the local density of other ionised matter. Plasma may be the most abundant form of matter in the universe, although this is currently tentative based on the existence. Plasma is mostly associated with the Sun and stars, extending to the rarefied intracluster medium, Plasma was first identified in a Crookes tube, and so described by Sir William Crookes in 1879. The nature of the Crookes tube cathode ray matter was identified by British physicist Sir J. J. The term plasma was coined by Irving Langmuir in 1928, perhaps because the glowing discharge molds itself to the shape of the Crookes tube and we shall use the name plasma to describe this region containing balanced charges of ions and electrons. Plasma is a neutral medium of unbound positive and negative particles. Although these particles are unbound, they are not ‘free’ in the sense of not experiencing forces, in turn this governs collective behavior with many degrees of variation. The average number of particles in the Debye sphere is given by the plasma parameter, bulk interactions, The Debye screening length is short compared to the physical size of the plasma. This criterion means that interactions in the bulk of the plasma are more important than those at its edges, when this criterion is satisfied, the plasma is quasineutral. Plasma frequency, The electron plasma frequency is compared to the electron-neutral collision frequency. When this condition is valid, electrostatic interactions dominate over the processes of ordinary gas kinetics, for plasma to exist, ionization is necessary. The term plasma density by itself refers to the electron density, that is. The degree of ionization of a plasma is the proportion of atoms that have lost or gained electrons, even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma. The degree of ionization, α, is defined as α = n i n i + n n, where n i is the number density of ions and n n is the number density of neutral atoms
13.
Parsec
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The parsec is a unit of length used to measure large distances to objects outside the Solar System. One parsec is the distance at which one astronomical unit subtends an angle of one arcsecond, a parsec is equal to about 3.26 light-years in length. The nearest star, Proxima Centauri, is about 1.3 parsecs from the Sun, most of the stars visible to the unaided eye in the nighttime sky are within 500 parsecs of the Sun. The parsec unit was likely first suggested in 1913 by the British astronomer Herbert Hall Turner, named from an abbreviation of the parallax of one arcsecond, it was defined so as to make calculations of astronomical distances quick and easy for astronomers from only their raw observational data. Partly for this reason, it is still the unit preferred in astronomy and astrophysics, though the light-year remains prominent in science texts. This corresponds to the definition of the parsec found in many contemporary astronomical references. Derivation, create a triangle with one leg being from the Earth to the Sun. As that point in space away, the angle between the Sun and Earth decreases. A parsec is the length of that leg when the angle between the Sun and Earth is one arc-second. One of the oldest methods used by astronomers to calculate the distance to a star is to record the difference in angle between two measurements of the position of the star in the sky. The first measurement is taken from the Earth on one side of the Sun, and the second is approximately half a year later. The distance between the two positions of the Earth when the two measurements were taken is twice the distance between the Earth and the Sun. The difference in angle between the two measurements is twice the angle, which is formed by lines from the Sun. Then the distance to the star could be calculated using trigonometry. 5-parsec distance of 61 Cygni, the parallax of a star is defined as half of the angular distance that a star appears to move relative to the celestial sphere as Earth orbits the Sun. Equivalently, it is the angle, from that stars perspective. The star, the Sun and the Earth form the corners of a right triangle in space, the right angle is the corner at the Sun. Therefore, given a measurement of the angle, along with the rules of trigonometry. A parsec is defined as the length of the adjacent to the vertex occupied by a star whose parallax angle is one arcsecond
14.
SN 1987A
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SN 1987A was a supernova in the outskirts of the Tarantula Nebula in the Large Magellanic Cloud. It occurred approximately 51.4 kiloparsecs from Earth and this was close enough that it was easily visible to the naked eye and it could be seen from the Southern Hemisphere. It was the closest observed supernova since SN1604, which occurred in the Milky Way itself, the light from the new supernova reached Earth on February 23,1987. As the first supernova discovered in 1987, it was labeled “1987A” and its brightness peaked in May with an apparent magnitude of about 3 and slowly declined in the following months. It was the first opportunity for astronomers to study the development of a supernova in great detail. This definitely proved the radioactive nature of the long-duration post-explosion glow of supernovae, SN 1987A was discovered by Ian Shelton and Oscar Duhalde at the Las Campanas Observatory in Chile on February 24,1987, and within the same 24 hours independently by Albert Jones in New Zealand. On March 4–12,1987, it was observed from space by Astron, four days after the event was recorded, the progenitor star was tentatively identified as Sanduleak −69°202, a blue supergiant. After the supernova faded, that identification was confirmed by Sanduleak −69°202 having disappeared. This was an identification, because models of high mass stellar evolution at the time did not predict that blue supergiants are susceptible to a supernova event. Many models of the progenitor have since attributed the color to its composition, particularly the low levels of heavy elements. There was some speculation that the star might have merged with a companion star prior to the supernova, because blue supergiant supernovae are not as bright as those generated by red supergiants, we cannot see them in as large a volume. We would thus not expect to see as many of them, approximately two to three hours before the visible light from SN 1987A reached Earth, a burst of neutrinos was observed at three separate neutrino observatories. This is likely due to emission, which occurs simultaneously with core collapse. Transmission of visible light is a process that occurs only after the shock wave reaches the stellar surface. At 07,35 UT, Kamiokande II detected 12 antineutrinos, IMB,8 antineutrinos, approximately three hours earlier, the Mont Blanc liquid scintillator detected a five-neutrino burst, but this is generally not believed to be associated with SN 1987A. The Kamiokande II detection, which at 12 neutrinos had the largest sample population, the first pulse, which started at 07,35,35 comprised 9 neutrinos, all of which arrived over a period of 1.915 seconds. A second pulse of three neutrinos arrived between 9.219 and 12.439 seconds after the first neutrino was detected, for a duration of 3.220 seconds. Although only 25 neutrinos were detected during the event, it was a significant increase from the previously observed background level and this was the first time neutrinos known to be emitted from a supernova had been observed directly, which marked the beginning of neutrino astronomy
15.
Large Magellanic Cloud
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The Large Magellanic Cloud is a satellite galaxy of the Milky Way. The LMC has a diameter of about 14,000 light-years, the LMC is the fourth-largest galaxy in the Local Group, after the Andromeda Galaxy, the Milky Way, and the Triangulum Galaxy. The LMC is classified as a Magellanic spiral and it contains a very prominent bar in its center, suggesting that it may have been a barred dwarf spiral galaxy before its spiral arms were disrupted, likely by the Milky Ways gravity. The LMCs present irregular appearance is likely the result of interactions with both the Milky Way and the Small Magellanic Cloud. The first recorded mention of the Large Magellanic Cloud was by the Persian astronomer Abd al-Rahman al-Sufi Shirazi, the next recorded observation was in 1503–4 by Amerigo Vespucci in a letter about his third voyage. In this letter he mentions three Canopes, two bright and one obscure, bright refers to the two Magellanic Clouds, and obscure refers to the Coalsack, ferdinand Magellan sighted the LMC on his voyage in 1519, and his writings brought the LMC into common Western knowledge. The galaxy now bears his name, measurements with the Hubble Space Telescope, announced in 2006, suggest the Large and Small Magellanic Clouds may be moving too fast to be orbiting the Milky Way. The Large Magellanic Cloud is usually considered an irregular galaxy, however, it shows signs of a bar structure, and is often reclassified as a Magellanic-type dwarf spiral galaxy. The Large Magellanic Cloud has a prominent central bar and a spiral arm, the central bar seems to be warped so that the east and west ends are nearer the Milky Way than the middle. In 2014, measurements from the Hubble Space Telescope made it possible to determine that the LMC has a period of 250 million years. The LMC was long considered to be a galaxy that could be assumed to lie at a single distance from the Solar System. However, in 1986, Caldwell and Coulson found that field Cepheid variables in the northeast portion of the LMC lie closer to the Milky Way than Cepheids in the southwest portion. More recently, this inclined geometry for field stars in the LMC has been confirmed via observations of Cepheids, core helium-burning red clump stars, all three of these papers find an inclination of ~35°, where a face-on galaxy has an inclination of 0°. Further work on the structure of the LMC using the kinematics of stars showed that the LMCs disk is both thick and flared. These results were confirmed by Grocholski et al. who calculated distances to a number of clusters, the distance to the LMC has been calculated using a variety of standard candles, with Cepheid variables being one of the most popular. Cepheids have been shown to have a relationship between their absolute luminosity and the period over which their brightness varies, however, Cepheids appear to suffer from a metallicity effect, where Cepheids of different metallicities have different period–luminosity relations. Unfortunately, the Cepheids in the Milky Way typically used to calibrate the period–luminosity relation are more rich than those found in the LMC. Modern 8-meter-class optical telescopes have discovered eclipsing binaries throughout the Local Group, parameters of these systems can be measured without mass or compositional assumptions
16.
SN 1572
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SN1572, B Cassiopeiae, or 3C10 was a supernova of Type Ia in the constellation Cassiopeia, one of about eight supernovae visible to the naked eye in historical records. It appeared in early November 1572 and was discovered by many individuals. The appearance of the Milky Way supernova of 1572 belongs among the important observation events in the history of astronomy. It also challenged the Aristotelian dogma of the unchangeability of the realm of stars, Tycho was not the first to observe the 1572 supernova, although he was probably the most accurate observer of the object. Almost as accurate were his European colleagues, such as Wolfgang Schuler, Thomas Digges, John Dee, Francesco Maurolico, Jerónimo Muñoz, Tadeáš Hájek, or Bartholomäus Reisacher. The more reliable contemporary reports state that the new star itself burst forth sometime between November 2 and 6, in 1572, when it rivalled Venus in brightness, the supernova remained visible to the naked eye into 1574, gradually fading until it disappeared from view. The distance to the remnant has been estimated to between 2 and 5 kpc, but recent studies suggest a value closer to 2.5 and 3 kpc. The search for a remnant was negative until 1952, when Hanbury Brown and Cyril Hazard reported a radio detection at 158.5 MHz. There is no dispute that 3C10 is the remnant of the supernova observed in 1572–1573, following a review article by Minkowski, the designation 3C10 appears to be that most commonly used in the literature when referring to the radio remnant of B Cas. Because the radio remnant was reported before the optical supernova-remnant wisps were discovered, the supernova remnant of B Cas was discovered in the 1960s by scientists with a Palomar Mountain telescope as a very faint nebula. It was later photographed by a telescope on the international ROSAT spacecraft, the supernova has been confirmed as Type Ia, in which a white dwarf star has accreted matter from a companion until it approaches the Chandrasekhar limit and explodes. This type of supernova does not typically create the spectacular nebula more typical of Type II supernovas, a shell of gas is still expanding from its center at about 9,000 km/s. A recent study indicates a rate of expansion below 5,000 km/s, in October 2004, a letter in Nature reported the discovery of a G2 star, similar in type to our own Sun and named Tycho G. It is thought to be the star that contributed mass to the white dwarf that ultimately resulted in the supernova. This find has been challenged in recent years, the star is relatively far away from the center and does not show rotation which might be expected of a companion star. In September 2008, the Subaru telescope obtained the spectrum of Tycho Brahes supernova near maximum brightness from a scattered-light echo. It has been confirmed that SN1572 belongs to the majority class of normal SNe Ia, an X-ray source designated Cepheus X-1 was detected by the Uhuru X-ray observatory at 4U 0022+63. Earlier catalog designations are X120+2 and XRS 00224+638, Cepheus X-1 is actually in the constellation Cassiopeia, and it is SN1572, the Tycho SNR
17.
Tycho Brahe
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Tycho Brahe, born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations. He was born in the then Danish peninsula of Scania, well known in his lifetime as an astronomer, astrologer and alchemist, he has been described as the first competent mind in modern astronomy to feel ardently the passion for exact empirical facts. His observations were some five times more accurate than the best available observations at the time, an heir to several of Denmarks principal noble families, he received a comprehensive education. He took an interest in astronomy and in the creation of more instruments of measurement. His system correctly saw the Moon as orbiting Earth, and the planets as orbiting the Sun, furthermore, he was the last of the major naked eye astronomers, working without telescopes for his observations. In his De nova stella of 1573, he refuted the Aristotelian belief in a celestial realm. Using similar measurements he showed that comets were also not atmospheric phenomena, as previously thought, on the island he founded manufactories, such as a paper mill, to provide material for printing his results. He built an observatory at Benátky nad Jizerou, there, from 1600 until his death in 1601, he was assisted by Johannes Kepler, who later used Tychos astronomical data to develop his three laws of planetary motion. Tychos body has been exhumed twice, in 1901 and 2010, to examine the circumstances of his death, both of his grandfathers and all of his great grandfathers had served as members of the Danish kings Privy Council. His paternal grandfather and namesake Thyge Brahe was the lord of Tosterup Castle in Scania, Tychos father Otte Brahe, like his father a royal Privy Councilor, married Beate Bille, who was herself a powerful figure at the Danish court holding several royal land titles. Both parents are buried under the floor of Kågeröd Church, four kilometres east of Knutstorp, Tycho was born at his familys ancestral seat of Knutstorp Castle, about eight kilometres north of Svalöv in then Danish Scania. He was the oldest of 12 siblngs,8 of whom lived to adulthood and his twin brother died before being baptized. Tycho later wrote an ode in Latin to his dead twin, an epitaph, originally from Knutstorp, but now on a plaque near the church door, shows the whole family, including Tycho as a boy. When he was two years old Tycho was taken away to be raised by his uncle Jørgen Thygesen Brahe. It is unclear why the Otte Brahe reached this arrangement with his brother, Tycho later wrote that Jørgen Brahe raised me and generously provided for me during his life until my eighteenth year, he always treated me as his own son and made me his heir. From ages 6 to 12, Tycho attended Latin school, probably in Nykøbing, at age 12, on 19 April 1559, Tycho began studies at the University of Copenhagen. There, following his uncles wishes, he studied law, but also studied a variety of other subjects, at the University, Aristotle was a staple of scientific theory, and Tycho likely received a thorough training in Aristotelian physics and cosmology. He experienced the solar eclipse of 21 August 1560, and was impressed by the fact that it had been predicted
18.
Kepler's Supernova
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Supernova 1604, also known as Keplers Supernova, Keplers Nova or Keplers Star, was a supernova of Type Ia that occurred in the Milky Way, in the constellation Ophiuchus. Visible to the eye, Keplers Star was brighter at its peak than any other star in the night sky. It was visible during the day for three weeks. The first recorded observation was in northern Italy on 9 October 1604, johannes Kepler began observing the luminous display on October 17 while working at the imperial court in Prague for Emperor Rudolf II. The supernova was recorded in Chinese and Korean sources. It was the supernova to be observed in a generation. No further supernovae have since been observed with certainty in the Milky Way, SN 1987A in the Large Magellanic Cloud was easily visible to the naked eye. Strong present day astronomical evidence exists for a Milky Way supernova whose signal would have reached Earth ca,1680, and another whose light should have arrived ca. There is no record of either having been detected at the time. The supernova remnant resulting from Keplers supernova is considered to be one of the objects of its kind. List of supernova remnants Blair, William P. Long, Knox S. Vancura, a detailed optical study of Keplers supernova remnant. Archived from the original on 2013-10-17
19.
Johannes Kepler
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Johannes Kepler was a German mathematician, astronomer, and astrologer. A key figure in the 17th-century scientific revolution, he is best known for his laws of motion, based on his works Astronomia nova, Harmonices Mundi. These works also provided one of the foundations for Isaac Newtons theory of universal gravitation, Kepler was a mathematics teacher at a seminary school in Graz, where he became an associate of Prince Hans Ulrich von Eggenberg. Later he became an assistant to the astronomer Tycho Brahe in Prague and he was also a mathematics teacher in Linz, and an adviser to General Wallenstein. Kepler lived in an era when there was no distinction between astronomy and astrology, but there was a strong division between astronomy and physics. Kepler was born on December 27, the feast day of St John the Evangelist,1571 and his grandfather, Sebald Kepler, had been Lord Mayor of the city. By the time Johannes was born, he had two brothers and one sister and the Kepler family fortune was in decline and his father, Heinrich Kepler, earned a precarious living as a mercenary, and he left the family when Johannes was five years old. He was believed to have died in the Eighty Years War in the Netherlands and his mother Katharina Guldenmann, an innkeepers daughter, was a healer and herbalist. Born prematurely, Johannes claimed to have weak and sickly as a child. Nevertheless, he often impressed travelers at his grandfathers inn with his phenomenal mathematical faculty and he was introduced to astronomy at an early age, and developed a love for it that would span his entire life. At age six, he observed the Great Comet of 1577, in 1580, at age nine, he observed another astronomical event, a lunar eclipse, recording that he remembered being called outdoors to see it and that the moon appeared quite red. However, childhood smallpox left him with vision and crippled hands. In 1589, after moving through grammar school, Latin school, there, he studied philosophy under Vitus Müller and theology under Jacob Heerbrand, who also taught Michael Maestlin while he was a student, until he became Chancellor at Tübingen in 1590. He proved himself to be a mathematician and earned a reputation as a skilful astrologer. Under the instruction of Michael Maestlin, Tübingens professor of mathematics from 1583 to 1631 and he became a Copernican at that time. In a student disputation, he defended heliocentrism from both a theoretical and theological perspective, maintaining that the Sun was the source of motive power in the universe. Despite his desire to become a minister, near the end of his studies, Kepler was recommended for a position as teacher of mathematics and he accepted the position in April 1594, at the age of 23. Keplers first major work, Mysterium Cosmographicum, was the first published defense of the Copernican system
20.
Interstellar medium
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In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and it fills interstellar space and blends smoothly into the surrounding intergalactic space. The energy that occupies the same volume, in the form of radiation, is the interstellar radiation field. The interstellar medium is composed of phases, distinguished by whether matter is ionic, atomic, or molecular. The interstellar medium is composed primarily of hydrogen followed by helium with trace amounts of carbon, oxygen, the thermal pressures of these phases are in rough equilibrium with one another. Magnetic fields and turbulent motions also provide pressure in the ISM, in all phases, the interstellar medium is extremely tenuous by terrestrial standards. In cool, dense regions of the ISM, matter is primarily in molecular form, in hot, diffuse regions of the ISM, matter is primarily ionized, and the density may be as low as 10−4 ions per cm3. Compare this with a density of roughly 1019 molecules per cm3 for air at sea level. By mass, 99% of the ISM is gas in any form, and 1% is dust. Of the gas in the ISM, by number 91% of atoms are hydrogen and 9% are helium, with 0. 1% being atoms of elements heavier than hydrogen or helium, by mass this amounts to 70% hydrogen, 28% helium, and 1. 5% heavier elements. The hydrogen and helium are primarily a result of primordial nucleosynthesis, the ISM plays a crucial role in astrophysics precisely because of its intermediate role between stellar and galactic scales. Stars form within the densest regions of the ISM, molecular clouds, and replenish the ISM with matter and energy through planetary nebulae, stellar winds, and supernovae. This interplay between stars and the ISM helps determine the rate at which a galaxy depletes its gaseous content, voyager 1 reached the ISM on August 25,2012, making it the first artificial object from Earth to do so. Interstellar plasma and dust will be studied until the end in 2025. Table 1 shows a breakdown of the properties of the components of the ISM of the Milky Way, field, Goldsmith & Habing put forward the static two phase equilibrium model to explain the observed properties of the ISM. Their modeled ISM consisted of a dense phase, consisting of clouds of neutral and molecular hydrogen. McKee & Ostriker added a third phase that represented the very hot gas which had been shock heated by supernovae. These phases are the temperatures where heating and cooling can reach a stable equilibrium and their paper formed the basis for further study over the past three decades
21.
Blast wave
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A blast wave in fluid dynamics is the pressure and flow resulting from the deposition of a large amount of energy in a small very localised volume. The flow field can be approximated as a shock wave. In simpler terms, a blast wave is an area of pressure expanding supersonically outward from an explosive core and it has a leading shock front of compressed gases. The blast wave is followed by a blast wind of negative pressure, the blast wave is harmful especially when one is very close to the center or at a location of constructive interference. High explosives, which detonate, generate blast waves, high-order explosives are more powerful than low-order explosives. HE detonate to produce a defining supersonic over-pressurization shock wave, several sources of HE include trinitrotoluene, C-4, Semtex, nitroglycerin, and ammonium nitrate fuel oil. LE deflagrate to create an explosion and lack HE’s over-pressurization wave. Sources of LE include pipe bombs, gunpowder, and most pure petroleum-based incendiary bombs such as Molotov cocktails or aircraft improvised as guided missiles, HE and LE induce different injury patterns. Only HE produce true blast waves, the classic flow solution—the so-called similarity solution—was independently devised by John von Neumann and British mathematician Geoffrey Ingram Taylor during World War II. After the war, the similarity solution was published by three other authors—L, sedov, R. Latter, and J. Lockwood-Taylor—who had discovered it independently. Since the early theoretical work more than 50 years ago, both theoretical and experimental studies of blast waves have been ongoing, the simplest form of a blast wave has been described and termed the Friedlander waveform. It occurs when a high explosive detonates in a free field, Blast waves have properties predicted by the physics of waves. For example, they can diffract through an opening. Like light or sound waves, when a blast wave reaches a boundary between two materials, part of it is transmitted, part of it is absorbed, and part of it is reflected, the impedances of the two materials determine how much of each occurs. The equation for a Friedlander waveform describes the pressure of the blast wave as a function of time, where Ps is the peak pressure and t* is the time at which the pressure first crosses the horizontal axis. Blast waves will wrap around objects and buildings, therefore, persons or objects behind a large building are not necessarily protected from a blast that starts on the opposite side of the building. Scientists use sophisticated mathematical models to predict how objects will respond to a blast in order to design effective barriers, anything in this area experiences peak pressures that can be several times higher than the peak pressure of the original shock front. In physics, interference is the meeting of two correlated waves and either increasing or lowering the net amplitude, depending on whether it is constructive or destructive interference, similarly two troughs make a trough of increased amplitude
22.
X-ray
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X-radiation is a form of electromagnetic radiation. Most X-rays have a wavelength ranging from 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz, X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. Spelling of X-ray in the English language includes the variants x-ray, xray, X-rays with high photon energies are called hard X-rays, while those with lower energy are called soft X-rays. Due to their ability, hard X-rays are widely used to image the inside of objects, e. g. in medical radiography. The term X-ray is metonymically used to refer to an image produced using this method. Since the wavelengths of hard X-rays are similar to the size of atoms they are useful for determining crystal structures by X-ray crystallography. By contrast, soft X-rays are easily absorbed in air, the length of 600 eV X-rays in water is less than 1 micrometer. There is no consensus for a definition distinguishing between X-rays and gamma rays, one common practice is to distinguish between the two types of radiation based on their source, X-rays are emitted by electrons, while gamma rays are emitted by the atomic nucleus. This definition has problems, other processes also can generate these high-energy photons. One common alternative is to distinguish X- and gamma radiation on the basis of wavelength, with radiation shorter than some arbitrary wavelength, such as 10−11 m and this criterion assigns a photon to an unambiguous category, but is only possible if wavelength is known. Occasionally, one term or the other is used in specific contexts due to precedent, based on measurement technique. Thus, gamma-rays generated for medical and industrial uses, for radiotherapy, in the ranges of 6–20 MeV. X-ray photons carry enough energy to ionize atoms and disrupt molecular bonds and this makes it a type of ionizing radiation, and therefore harmful to living tissue. A very high radiation dose over a period of time causes radiation sickness. In medical imaging this increased risk is generally greatly outweighed by the benefits of the examination. The ionizing capability of X-rays can be utilized in treatment to kill malignant cells using radiation therapy. It is also used for material characterization using X-ray spectroscopy, hard X-rays can traverse relatively thick objects without being much absorbed or scattered. For this reason, X-rays are widely used to image the inside of visually opaque objects, the most often seen applications are in medical radiography and airport security scanners, but similar techniques are also important in industry and research
23.
Hydrogen
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Hydrogen is a chemical element with chemical symbol H and atomic number 1. With a standard weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form is the most abundant chemical substance in the Universe, non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton, the universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays an important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a charge when it is known as a hydride. The hydrogen cation is written as though composed of a bare proton, Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing and ammonia production, mostly for the fertilizer market, Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks. Hydrogen gas is flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion is −286 kJ/mol,2 H2 + O2 →2 H2O +572 kJ Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%, the explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C, the detection of a burning hydrogen leak may require a flame detector, such leaks can be very dangerous. Hydrogen flames in other conditions are blue, resembling blue natural gas flames, the destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a mixture of hydrogen to oxygen combined with carbon compounds from the airship skin. H2 reacts with every oxidizing element, the ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 91 nm wavelength. The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, however, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity. The most complicated treatments allow for the effects of special relativity
24.
Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
25.
Nebular hypothesis
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The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System. It suggests that the Solar System formed from nebulous material, the theory was developed by Immanuel Kant and published in his Allgemeine Naturgeschichte und Theorie des Himmels, published in 1755. Originally applied to the Solar System, the process of planetary formation is now thought to be at work throughout the Universe. The widely-accepted modern variant of the hypothesis is the solar nebular disk model or solar nebular model. It offered explanations for a variety of properties of the Solar System, including the circular and coplanar orbits of the planets. Some elements of the hypothesis are echoed in modern theories of planetary formation. According to the hypothesis, stars form in massive and dense clouds of molecular hydrogen—giant molecular clouds. These clouds are gravitationally unstable, and matter coalesces within them to smaller denser clumps, which rotate, collapse. Star formation is a process, which always produces a gaseous protoplanetary disk, proplyd. This may give birth to planets in certain circumstances, which are not well known, thus the formation of planetary systems is thought to be a natural result of star formation. A Sun-like star usually takes approximately 1 million years to form, the protoplanetary disk is an accretion disk that feeds the central star. Initially very hot, the disk later cools in what is known as the T tauri star stage, here, formation of small dust grains made of rocks, the grains eventually may coagulate into kilometer-sized planetesimals. If the disk is massive enough, the runaway accretions begin, near the star, the planetary embryos go through a stage of violent mergers, producing a few terrestrial planets. The last stage takes approximately 100 million to a billion years, the formation of giant planets is a more complicated process. It is thought to occur beyond the frost line, where planetary embryos mainly are made of various types of ice, as a result, they are several times more massive than in the inner part of the protoplanetary disk. What follows after the formation is not completely clear. Some embryos appear to continue to grow and eventually reach 5–10 Earth masses—the threshold value, jupiter- and Saturn-like planets are thought to accumulate the bulk of their mass during only 10,000 years. The accretion stops when the gas is exhausted, the formed planets can migrate over long distances during or after their formation
26.
Cassiopeia A
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Cassiopeia A is a supernova remnant in the constellation Cassiopeia and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. The supernova occurred approximately 11,000 light-years away within the Milky Way, the expanding cloud of material left over from the supernova now appears approximately 10 light-years across from Earths perspective. In wavelengths of light, it has been seen with amateur telescopes down to 234mm with filters. Possible explanations lean toward the idea that the star was unusually massive and had previously ejected much of its outer layers. These outer layers would have cloaked the star and re-absorbed much of the released as the inner star collapsed. Cas A was among the first discrete astronomical radio sources found and its discovery was reported in 1948 by Martin Ryle and Francis Graham-Smith, astronomers at Cambridge, based on observations with the Long Michelson Interferometer. The optical component was first identified in 1950, Cas A is 3C461 in the Third Cambridge Catalogue of Radio Sources and G111. 7-2.1 in the Green Catalog of Supernova Remnants. Calculations working back from the currently observed expansion point to an explosion that would have become visible on Earth around 1667, at any rate, no supernova occurring within the Milky Way has been visible to the naked eye from Earth since. The expansion shell has a temperature of around 50 million degrees Fahrenheit, Cas A had a flux density of 2720 ±50 Jy at 1 GHz in 1980. Because the supernova remnant is cooling, its density is decreasing. At 1 GHz, its density is decreasing at a rate of 0.97 ±0.04 percent per year. This decrease means that, at frequencies below 1 GHz, Cas A is now less intense than Cygnus A. Cas A is still the brightest extrasolar radio source in the sky at frequencies above 1 GHz, in 1979, Shklovsky predicted that Cas A had a black hole. In 1999, the Chandra X-Ray Observatory found a hot point-like source close to the center of the nebula that is likely the neutron star or black hole predicted. Although Cas X-1, the apparent first X-ray source in the constellation Cassiopeia was not detected during the June 16,1964, Aerobee sounding rocket flight, it was considered as a possible source. Cas A was scanned during another Aerobee rocket flight of October 1,1964, Cas XR-1 was discovered by an Aerobee rocket flight on April 25,1965, at RA 23h 21m Dec +58° 30′. Cas X-1 is Cas A, a Type II SNR at RA 23h 18m Dec +58° 30′, the designations Cassiopeia X-1, Cas XR-1, Cas X-1 are no longer used, but the X-ray source is Cas A at 2U 2321+58. Recently, an echo of the Cassiopeia A explosion was observed on nearby gas clouds using Spitzer Space Telescope. In 2013, astronomers detected phosphorus in Cassiopeia A, which confirmed that this element is produced in supernovae through supernova nucleosynthesis, the phosphorus-to-iron ratio in material from the supernova remnant could be up to 100 times higher than in the Milky Way in general
27.
Pulsar wind nebula
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A pulsar wind nebula, sometimes called a plerion, is a type of nebula found inside the shells of supernova remnants that is powered by pulsar winds generated by its central pulsar. These nebulae were discovered in 1976 as small depressions at radio wavelengths near the centre of supernova remnants and they have since been found to be X-ray emitters and are possibly γ-ray sources. As the plerion ages, the nebulosity of the supernova remnant dissipates, over time, pulsar wind nebulae may change in behaviour and become relic nebulae surrounding millisecond radio pulsars or even older and slower rotating pulsars. Plerions are estimated to last around 15,000 years, after which the shell dissipates as the energies from the pulsar decreases, importantly, this depends on the rate of energy lost by the pulsar as its spin rate slows, which varies among the known pulsars. Pulsar winds are composed of charged particles accelerated to relativistic speeds by the rapidly rotating, the pulsar wind often streams into the surrounding interstellar medium, creating a standing shock wave called the wind termination shock, where matter is decelerated to sub-relativistic speed. Beyond this radius, synchrotron emission increases in the magnetized flow and these processes can switch on and off with many reversals, and this creates the numerous visible shells centred on the pulsar. Pulsar wind nebulae often show the properties, An increasing brightness towards the center. A highly polarized flux and a spectral index in the radio band. The index steepens at X-ray energies due to radiation losses. An X-ray size that is smaller than their radio and optical size. A photon index at TeV gamma-ray energies of ~2.3, Pulsar wind nebulae can be powerful probes of a pulsar/neutron stars interaction with its surroundings. Their unique properties can be used to infer the geometry, energetics, and composition of the wind, the space velocity of the pulsar itself. G292. 0+01.8 The Pulsar Wind Nebula Catalog
28.
Pulsar
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A pulsar is a highly magnetized, rotating neutron star or white dwarf, that emits a beam of electromagnetic radiation. This radiation can be observed only when the beam of emission is pointing toward Earth, neutron stars are very dense, and have short, regular rotational periods. This produces a very precise interval between pulses that range from milliseconds to seconds for an individual pulsar, Pulsars are believed to be one of the candidates of high and ultra-high energy astroparticles. The precise periods of pulsars make them very useful tools, observations of a pulsar in a binary neutron star system were used to indirectly confirm the existence of gravitational radiation. The first extrasolar planets were discovered around a pulsar, PSR B1257+12, certain types of pulsars rival atomic clocks in their accuracy in keeping time. The first pulsar was observed on November 28,1967, by Jocelyn Bell Burnell and they observed pulses separated by 1.33 seconds that originated from the same location on the sky, and kept to sidereal time. When observations with another telescope confirmed the emission, it eliminated any sort of instrumental effects and it is an interesting problem—if one thinks one may have detected life elsewhere in the universe, how does one announce the results responsibly. Even so, they nicknamed the signal LGM-1, for little green men and it was not until a second pulsating source was discovered in a different part of the sky that the LGM hypothesis was entirely abandoned. Their pulsar was later dubbed CP1919, and is now known by a number of designators including PSR 1919+21, PSR B1919+21, although CP1919 emits in radio wavelengths, pulsars have, subsequently, been found to emit in visible light, X-ray, and/or gamma ray wavelengths. The word pulsar is a portmanteau of pulsating star, and first appeared in print in 1968, An entirely novel kind of came to light on Aug.6 last year and was referred to, by astronomers. Now it is thought to be a novel type between a white dwarf and a neutron, the name Pulsar is likely to be given to it. Dr. A. Hewish told me yesterday, … I am sure that today every radio telescope is looking at the Pulsars. The existence of stars was first proposed by Walter Baade and Fritz Zwicky in 1934. The discovery of the Crab pulsar later in 1968 seemed to provide confirmation of the neutron star model of pulsars. The Crab pulsar has a 33-millisecond pulse period, which was too short to be consistent with other proposed models for pulsar emission. Moreover, the Crab pulsar is so named because it is located at the center of the Crab Nebula, consistent with the 1933 prediction of Baade and Zwicky. Considerable controversy is associated with the fact that Professor Hewish was awarded the prize while Bell, Bell claims no bitterness upon this point, supporting the decision of the Nobel prize committee. In 1974, Joseph Hooton Taylor, Jr. and Russell Hulse discovered for the first time a pulsar in a binary system and this pulsar orbits another neutron star with an orbital period of just eight hours
29.
Galactic cosmic ray
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Cosmic rays are high-energy radiation, mainly originating outside the Solar System. Upon impact with the Earths atmosphere, cosmic rays can produce showers of particles that sometimes reach the surface. Composed primarily of protons and atomic nuclei, they are of mysterious origin. Data from the Fermi space telescope have been interpreted as evidence that a significant fraction of cosmic rays originate from the supernovae explosions of stars. Active galactic nuclei probably also produce cosmic rays, the term ray is a historical accident, as cosmic rays were at first, and wrongly, thought to be mostly electromagnetic radiation. In current usage, the cosmic ray almost exclusively refers to massive particles. Massive particles – those that have rest mass – can gain additional, kinetic, mass-energy when they are moving, through this process, some particles acquire tremendously high mass-energies. These are significantly higher than the energy of even the highest-energy photons detected to date. The energy of the massless photon depends solely on frequency, not speed, at the higher end of the energy spectrum, relativistic kinetic energy is the main source of the mass-energy of cosmic rays. Hence, the highest-energy detected fermionic cosmic ray was around 3×106 times more energetic than the highest-energy detected cosmic photons, of primary cosmic rays, which originate outside of Earths atmosphere, about 99% are the nuclei of well-known atoms, and about 1% are solitary electrons. Of the nuclei, about 90% are simple protons, i. e. hydrogen nuclei, 9% are alpha particles, identical to helium nuclei, a very small fraction are stable particles of antimatter, such as positrons or antiprotons. The precise nature of this fraction is an area of active research. An active search from Earth orbit for anti-alpha particles has failed to detect them, one can show that such enormous energies might be achieved by means of the Centrifugal mechanism of acceleration in Active galactic nuclei. At 50 J, the highest-energy ultra-high-energy cosmic rays have energies comparable to the energy of a 90-kilometre-per-hour baseball. As a result of discoveries, there has been interest in investigating cosmic rays of even greater energies. Most cosmic rays, however, do not have such extreme energies, however, his paper published in Physikalische Zeitschrift was not widely accepted. In 1911 Domenico Pacini observed simultaneous variations of the rate of ionization over a lake, over the sea, Pacini concluded from the decrease of radioactivity underwater that a certain part of the ionization must be due to sources other than the radioactivity of the Earth. In 1912, Victor Hess carried three enhanced-accuracy Wulf electrometers to an altitude of 5300 meters in a balloon flight
30.
Fritz Zwicky
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Fritz Zwicky was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, in 1933, Zwicky was the first to use the virial theorem to infer the existence of unseen dark matter, describing it as dunkle Materie. Fritz Zwicky was born in Varna, in the Principality of Bulgaria and his father, Fridolin, was a prominent industrialist in the Bulgarian city and also served as ambassador of Norway in Varna. The Zwicky House in Varna was designed and built by Fridolin Zwicky, fritzs mother, Franziska Vrček, was an ethnic Czech of the Austro-Hungarian Empire. Fritz was the oldest of the Zwicky familys three children, he had a brother named Rudolf and a sister, Leonie. Fritzs mother died in Varna in 1927, and his father Fridolin remained in Bulgaria until 1945 and his sister Leonie married a Bulgarian from Varna and spent her entire life in the city. In 1904, at the age of six, Fritz was sent to his grandparents in the familys ancestral canton in Glarus, Switzerland, to study commerce. His interests shifted to math and physics and he received an education in mathematics and experimental physics at the Swiss Federal Polytechnic, located in Zurich. He was responsible for positing numerous cosmological theories that have a impact on the understanding of our universe today. He was the first to coin the term supernova during his fostering the concept of neutron stars, Zwicky was a lone wolf and did all of his own mathematical work. He intended to write an autobiography titled, Operation Lone Wolf and it would be five years later when Oppenheimer would publish his landmark paper announcing neutron stars. He developed some of the earliest jet engines and holds over 50 patents, many in jet propulsion, and is the inventor of the Underwater Jet, the Two Piece Jet Thrust Motor and Inverted Hydro Pulse. In April 1932, Fritz Zwicky married Dorothy Vernon Gates, a member of a prominent local family and her money was instrumental in the funding of the Palomar Observatory during the Great Depression. Nicholas Roosevelt, cousin of President Theodore Roosevelt, was his brother-in-law by marriage to Tirzah Gates, Zwicky and Dorothy divorced amicably in 1941. In 1947 Zwicky was married in Switzerland to Anna Margaritha Zurcher, Zwicky died in Pasadena on February 8,1974, and was buried in Mollis, Switzerland. He is remembered as both a genius and a curmudgeon, one of his favorite insults was to refer to people he did not approve of as spherical bastards, because, he explained, they were bastards no matter which way you looked at them. A recent biography in English was published by the Fritz Zwicky Foundation, Alfred Stöckli & Roland Müller, a review of the book is available from Acta Morphologica Generalis. Fritz Zwicky was a prolific scientist and made important contributions in areas of astronomy
31.
Vitaly Ginzburg
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He was the successor to Igor Tamm as head of the Department of Theoretical Physics of the Lebedev Physical Institute of the Russian Academy of Sciences, and an outspoken atheist. He defended his candidates dissertation in 1940, and his doctors dissertation in 1942, in 1944, he became a member of the Communist Party of the Soviet Union. In 1937, Ginzburg married Olga Zamsha, in 1946 he married his second wife, Nina Ginzburg, who had spent more than a year in custody on fabricated charges of plotting to assassinate the Soviet leader Joseph Stalin. Ginzburg was the editor-in-chief of the scientific journal Uspekhi Fizicheskikh Nauk and he also headed the Academic Department of Physics and Astrophysics Problems, which Ginzburg founded at the Moscow Institute of Physics and Technology in 1968. He is also known for fighting anti-Semitism and supporting the state of Israel. In the 2000s Ginzburg was politically active, supporting the Russian liberal opposition and he defended Igor Sutyagin and Valentin Danilov against charges of espionage put forth by the authorities. On April 2,2009, in an interview to the Radio Liberty Ginzburg denounced the FSB as an institution harmful to Russia, Ginzburg worked at the P. N. Lebedev Physical Institute of Soviet and Russian Academy of Sciences in Moscow since 1940. Russian Academy of Sciences is an institution where mostly all Nobel Prize laureates of physics from Russia have done their studies and/or research works. Ginzburg was an avowed atheist, both under the militantly atheist Soviet government and in post-Communist Russia when religion made a strong revival and he criticized clericalism in the press and wrote several books devoted to the questions of religion and atheism. Because of this, some Orthodox Christian groups denounced him and said no science award could excuse his verbal attacks on the Russian Orthodox Church. He was one of the signers of the Open letter to the President Vladimir V. Putin from the Members of the Russian Academy of Sciences against clericalisation of Russia. A spokeswoman for the Russian Academy of Sciences, announced that Ginzburg died in Moscow on November 8,2009 and he had been suffering from ill health for several years, and three years before his death said In general, I envy believers. I am 90, and being overcome by illnesses, for believers, it is easier to deal with them and with lifes other hardships. I cannot believe in resurrection after death, Ginzburg was buried on 11 November in the Novodevichy Cemetery in Moscow, the resting place of many famous politicians, writers and scientists of Russia. Obituary The Independent November 14,2009
32.
Enrico Fermi
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Enrico Fermi was an Italian physicist, who created the worlds first nuclear reactor, the Chicago Pile-1. He has been called the architect of the age and the architect of the atomic bomb. He was one of the few physicists to excel both theoretically and experimentally and he made significant contributions to the development of quantum theory, nuclear and particle physics, and statistical mechanics. Fermis first major contribution was to statistical mechanics, today, particles that obey the exclusion principle are called fermions. Later Pauli postulated the existence of an invisible particle emitted along with an electron during beta decay. Fermi took up this idea, developing a model that incorporated the postulated particle and his theory, later referred to as Fermis interaction and still later as weak interaction, described one of the four fundamental forces of nature. Fermi left Italy in 1938 to escape new Italian Racial Laws that affected his Jewish wife Laura Capon and he emigrated to the United States where he worked on the Manhattan Project during World War II. Fermi led the team designed and built Chicago Pile-1, which went critical on 2 December 1942. He was on hand when the X-10 Graphite Reactor at Oak Ridge, Tennessee, went critical in 1943, at Los Alamos he headed F Division, part of which worked on Edward Tellers thermonuclear Super bomb. He was present at the Trinity test on 16 July 1945, after the war, Fermi served under J. Robert Oppenheimer on the General Advisory Committee, which advised the Atomic Energy Commission on nuclear matters and policy. Following the detonation of the first Soviet fission bomb in August 1949 and he was among the scientists who testified on Oppenheimers behalf at the 1954 hearing that resulted in the denial of the latters security clearance. Enrico Fermi was born in Rome, Italy, on 29 September 1901 and he was the third child of Alberto Fermi, a division head in the Ministry of Railways, and Ida de Gattis, an elementary school teacher. His only sister, Maria, was two years older than he was, and his brother Giulio was a year older, after the two boys were sent to a rural community to be wet nursed, Enrico rejoined his family in Rome when he was two and a half. Although he was baptised a Roman Catholic in accordance with his grandparents wishes, his family was not particularly religious, as a young boy he shared the same interests as his brother Giulio, building electric motors and playing with electrical and mechanical toys. Giulio died during the administration of an anesthetic for an operation on a throat abscess in 1915, one of Fermis first sources for his study of physics was a book he found at the local market at Campo de Fiori in Rome. Published in 1840, the 900-page Elementorum physicae mathematicae, was written in Latin by Jesuit Father Andrea Caraffa and it covered mathematics, classical mechanics, astronomy, optics, and acoustics, insofar as these disciplines were understood when the book was written. Fermis interest in physics was encouraged by his fathers colleague Adolfo Amidei, who gave him several books on physics and mathematics. Fermi graduated from school in July 1918 and, at Amideis urging
33.
SN 1006
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Some reports state it was clearly visible in the daytime. Modern astronomers now consider its distance from us at about 7,200 light-years, egyptian astrologer and astronomer Ali ibn Ridwan, writing in a commentary on Ptolemys Tetrabiblos, stated that the spectacle was a large circular body, 2½ to 3 times as large as Venus. The sky was shining because of its light, the intensity of its light was a little more than a quarter that of Moon light. Like all other observers, Ali ibn Ridwan noted that the new star was low on the southern horizon, some astrologers interpreted the event as a portent of plague and famine. The most northerly sighting is recorded in the annals of the Abbey of Saint Gall in Switzerland and this description is often taken as probable evidence that the supernova was of Type Ia. Some sources state that the star was bright enough to cast shadows, according to Songshi, the official history of the Song Dynasty, the star seen on 1 May 1006 appeared to the south of constellation Di, east of Lupus and one degree to the west of Centaurus. It shone so brightly that objects on the ground could be seen at night, by December, it was again sighted in the constellation Di. The reported color yellow should be taken with some suspicion however, there appear to have been two distinct phases in the early evolution of this supernova. There was first a period at which it was at its brightest, after this period it diminished. A petroglyph by the Hohokam in White Tank Mountain Regional Park, on August 25,2015, a recently found document suggested that observers in Yemen may have seen SN1006 on April 17, two weeks before its previously assumed earliest observation. This is located near the star Beta Lupi, displaying a 30 arcmin circular shell, x-ray and optical emission from this remnant have also been detected, and during 2010 the H. E. S. S. Gamma-ray observatory announced the detection of very-high-energy gamma-ray emission from the remnant, no associated neutron star or black hole has been found, which is the situation expected for the remnant of a Type Ia supernova. Remnant SNR G327. 6+14.6 has a distance of 2.2 kpc. from Earth. The greatest risk is to the Earths protective ozone layer, producing effects on life, while SN1006 did not appear to have such significant effects, a signal of its outburst can be found in nitrate deposits in Antarctic ice
34.
Synchrotron radiation
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Synchrotron radiation is the electromagnetic radiation emitted when charged particles are accelerated radially, i. e. when they are subject to an acceleration perpendicular to their velocity. It is produced, for example, in synchrotrons using bending magnets, if the particle is non-relativistic, then the emission is called cyclotron emission. If, on the hand, the particles are relativistic, sometimes referred to as ultrarelativistic. Synchrotron radiation may be achieved artificially in synchrotrons or storage rings, the radiation produced in this way has a characteristic polarization and the frequencies generated can range over the entire electromagnetic spectrum which is also called continuum radiation. Pollock recounts, On April 24, Langmuir and I were running the machine and as usual were trying to push the electron gun, some intermittent sparking had occurred and we asked the technician to observe with a mirror around the protective concrete wall. He immediately signaled to turn off the synchrotron as he saw an arc in the tube, the vacuum was still excellent, so Langmuir and I came to the end of the wall and observed. At first we thought it might be due to Cherenkov radiation, when high-energy particles are in acceleration, including electrons forced to travel in a curved path by a magnetic field, synchrotron radiation is produced. This is similar to an antenna, but with the difference that, in theory. The radiated power is given by the relativistic Larmor formula while the force on the electron is given by the Abraham–Lorentz–Dirac force. The radiation pattern can be distorted from a dipole pattern into an extremely forward-pointing cone of radiation. Synchrotron radiation is the brightest artificial source of X-rays, the planar acceleration geometry appears to make the radiation linearly polarized when observed in the orbital plane, and circularly polarized when observed at a small angle to that plane. Amplitude and frequency are however focused to the polar ecliptic, electrons are accelerated to high speeds in several stages to achieve a final energy that is typically in the GeV range. Each proton may lose 6.7 keV per turn due to this phenomenon, Synchrotron radiation is also generated by astronomical objects, typically where relativistic electrons spiral through magnetic fields. Two of its characteristics include non-thermal power-law spectra, and polarization, solar flares accelerate particles that emit in this way, as suggested by R. Giovanelli in 1948 and described critically by J. H. Piddington in 1952. T. K. Breus noted that questions of priority on the history of astrophysical synchrotron radiation is complicated, writing, In particular, Ginzburg broke his relationships with I. S. Shklovsky and did not speak with him for 18 years, in the West, Thomas Gold and Sir Fred Hoyle were in dispute with H. Alfven and N. Herlofson, while K. O. Kiepenheuer and G. Hutchinson were ignored by them, such jets, the nearest being in Messier 87, have been confirmed by the Hubble telescope as apparently superluminal, travelling at 6 × c from our planetary frame. This phenomenon is caused because the jets are travelling very near the speed of light, because at every point of their path the high-velocity jets are emitting light, the light they emit does not approach the observer much more quickly than the jet itself
35.
Cherenkov Telescope Array
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The physics program of CTA goes beyond high energy astrophysics into cosmology and fundamental physics. CTA intends to improve the sensitivity of the current generation of IACTs such as MAGIC, HESS. It will foreseeably consist of tens of IACTs of different mirror sizes, production of the first telescope prototypes started in 2013. CTA is designed and will be built by a collaboration of scientists. The project is on the road-map of the European Strategy Forum on Research Infrastructures, the European Astroparticle Physics network ASPERA, the entire project, with its planned 19-dish array in the Northern Hemisphere and its 99-dish array in the Southern Hemisphere is expected to cost about 200 million €. The Namibian and Mexican sites will be kept as viable alternatives, on 26 March 2015, the CTA Resource Board, composed of representatives of ministries and funding agencies, decided to begin negotiations with two countries, Spain and Mexico. Arizona will be kept in consideration as a possible back-up site, after negotiations, the Board will select the final site in November 2015. Paranal Observatory First Choice to Host Worlds Largest Array of Gamma-ray Telescopes, the project is expected to move forward with construction of the first telescopes on site planned for 2016. Negotiations were expected to conclude in August 2015, Official web page of CTA Official web page of ESFRI Official website of ASPERA Official website of ASTRONET
36.
Local Bubble
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The Local Bubble is a cavity in the interstellar medium in the Orion Arm of the Milky Way. It contains, among others, the Local Interstellar Cloud, which contains the Solar System, the hot diffuse gas in the Local Bubble emits X-rays. The very sparse, hot gas of the Local Bubble is the result of supernovae that exploded within the past ten to twenty million years and it was once thought that the most likely candidate for the remains of this supernova was Geminga, a pulsar in the constellation Gemini. Later, however, it has suggested that multiple supernovae in subgroup B1 of the Pleiades moving group were more likely responsible. The Solar System has been traveling through the region occupied by the Local Bubble for the last five to ten million years. Its current location lies in the Local Interstellar Cloud, a region of denser material within the Bubble. The LIC formed where the Local Bubble and the Loop I Bubble met, the gas within the LIC has a density of approximately 0.3 atoms per cubic centimeter. It abuts other bubbles of less dense medium, including, in particular. The Loop I Bubble was created by supernovae and stellar winds in the Scorpius–Centaurus Association, the Loop I Bubble contains the star Antares, as shown on the diagram above right. Several tunnels connect the cavities of the Local Bubble with the Loop I Bubble, other bubbles which are adjacent to the Local Bubble are the Loop II Bubble and the Loop III Bubble. Launched in February 2003 and active until April 2008, a space observatory called Cosmic Hot Interstellar Plasma Spectrometer examined the hot gas within the Local Bubble. The Local Bubble was also the region of interest for the Extreme Ultraviolet Explorer mission, sources beyond the edge of the bubble were identified, but attenuated by the denser interstellar medium. Gould Belt List of nearest stars and brown dwarfs Orion–Eridanus Superbubble Perseus Arm Superbubble Anderson, dont stop till you get to the Fluff. Vergely, J. L. Crifo, F. Sfeir, a 3D map of the Milky Way Galaxy and the Orion Arm
37.
Planetary nebula
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A planetary nebula, often abbreviated as PN or plural PNe, is a kind of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from old red giant stars late in their lives. Herschels name for these objects was popularly adopted and has not been changed and they are a relatively short-lived phenomenon, lasting a few tens of thousands of years, compared to a typical stellar lifetime of several billion years. After most of the red giants atmosphere is dissipated, the radiation of the hot luminous core, called a planetary nebula nucleus. Absorbed ultraviolet light energises the shell of gas around the central star. Planetary nebulae likely play a role in the chemical evolution of the Milky Way by expelling elements to the interstellar medium from stars where those elements were created. Planetary nebulae are also observed in distant galaxies, yielding useful information about their chemical abundances. Starting from the 1990s, Hubble Space Telescope images have revealed many planetary nebulae to have extremely complex, about one-fifth are roughly spherical, but the majority are not spherically symmetric. The mechanisms that produce such a variety of shapes and features are not yet well understood. The first planetary nebula discovered was the Dumbbell Nebula in the constellation of Vulpecula and it was observed by Charles Messier in 1764 and listed as M27 in his catalogue of nebulous objects. To early observers with telescopes, M27 and subsequently discovered planetary nebulae resembled the giant planets like Uranus. William Herschel, discoverer of Uranus, eventually coined the term planetary nebula, the nature of planetary nebulae was unknown until the first spectroscopic observations were made in the mid-19th century. Using a prism to disperse their light, William Huggins was one of the earliest astronomers to study the spectra of astronomical objects. On August 29,1864, Huggins was the first to analyze the spectrum of a planetary nebula when he observed Cats Eye Nebula and his observations of stars showed that their spectra consisted of a continuum of radiation with many dark lines superimposed. He later found that many objects such as the Andromeda Nebula had spectra that were quite similar. Those nebulae were later shown to be collections of stars now called galaxies, however, when Huggins looked at the Cats Eye Nebula, he found a very different spectrum. Rather than a strong continuum with absorption lines superimposed, the Cats Eye Nebula, the brightest of these was at a wavelength of 500.7 nanometres, which did not correspond with a line of any known element. At first, it was hypothesized that the line might be due to an unknown element, a similar idea had led to the discovery of helium through analysis of the Suns spectrum in 1868. While helium was isolated on Earth soon after its discovery in the spectrum of the Sun, nebulium was not
38.
Superbubble
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A superbubble or supershell is a cavity which is hundreds of light years across, and is filled with 106 K gas blown into the interstellar medium by multiple supernovae and stellar winds. The winds of newly born stars strip superbubbles of any dust or gas, the most massive stars, with masses ranging from eight to roughly one hundred solar masses and spectral types of O and early B are usually found in groups called OB associations. Massive O stars have strong winds, and all of these stars explode as supernovae at the end of their lives. The strongest stellar winds release kinetic energy of 1051 ergs over the lifetime of a star and these winds can form stellar wind bubbles dozens of light years across. Inside OB associations, the stars are close enough that their wind bubbles merge, when stars die, supernova explosions, similarly, drive blast waves that can reach even larger sizes, with expansion velocities up to several hundred km s−1. Stars in OB associations are not gravitationally bound, but they drift apart at small speeds, as a result, most of their supernova explosions occur within the cavity formed by the stellar wind bubbles. These explosions never form a visible remnant, but instead expend their energy in the hot interior as sound waves. Both stellar winds and stellar explosions thus power the expansion of the superbubble in the interstellar medium, the interstellar gas swept up by superbubbles generally cools, forming a dense shell around the cavity. These shells were first observed in emission at twenty-one centimeters from hydrogen. They are also observed in X-ray emission from their hot interiors, in line emission from their ionized shells. Large enough superbubbles can blow through the galactic disk, releasing their energy into the surrounding galactic halo or even into the intergalactic medium. LHA 120-N44 in the Large Magellanic Cloud,1988, Annual Review of Astronomy and Astrophysics 26, 145-197
39.
BBC News
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BBC News is an operational business division of the British Broadcasting Corporation responsible for the gathering and broadcasting of news and current affairs. The department is the worlds largest broadcast news organisation and generates about 120 hours of radio and television output each day, the service maintains 50 foreign news bureaux with more than 250 correspondents around the world. James Harding has been Director of News and Current Affairs since April 2013, the departments annual budget is in excess of £350 million, it has 3,500 staff,2,000 of whom are journalists. BBC News domestic, global and online news divisions are housed within the largest live newsroom in Europe, parliamentary coverage is produced and broadcast from studios in Millbank in London. Through the BBC English Regions, the BBC also has regional centres across England, as well as national news centres in Northern Ireland, Scotland, all nations and English regions produce their own local news programmes and other current affairs and sport programmes. As with all media outlets, though, it has been accused of political bias from across the political spectrum. The British Broadcasting Company broadcast its first radio bulletin from radio station 2LO on 14 November 1922, on Easter weekend in 1930, this reliance on newspaper wire services left the radio news service with no information to report. The BBC gradually gained the right to edit the copy and, in 1934, however, it could not broadcast news before 6 PM until World War II. Gaumont British and Movietone cinema newsreels had been broadcast on the TV service since 1936, a weekly Childrens Newsreel was inaugurated on 23 April 1950, to around 350,000 receivers. The network began simulcasting its radio news on television in 1946, televised bulletins began on 5 July 1954, broadcast from leased studios within Alexandra Palace in London. The publics interest in television and live events was stimulated by Elizabeth IIs coronation in 1953 and it is estimated that up to 27 million people viewed the programme in the UK, overtaking radios audience of 12 million for the first time. Those live pictures were fed from 21 cameras in central London to Alexandra Palace for transmission and that year, there were around two million TV Licences held in the UK, rising to over three million the following year, and four and a half million by 1955. This was then followed by the customary Television Newsreel with a commentary by John Snagge. It was revealed that this had been due to producers fearing a newsreader with visible facial movements would distract the viewer from the story. On-screen newsreaders were finally introduced a year later in 1955 – Kenneth Kendall, Robert Dougall, mainstream television production had started to move out of Alexandra Palace in 1950 to larger premises – mainly at Lime Grove Studios in Shepherds Bush, west London – taking Current Affairs with it. It was from here that the first Panorama, a new programme, was transmitted on 11 November 1953. On 28 October 1957, the Today programme, a radio programme, was launched in central London on the Home Service. In 1958, Hugh Carleton Greene became head of News and Current Affairs and he set up a BBC study group whose findings, published in 1959, were critical of what the television news operation had become under his predecessor, Tahu Hole
40.
University of Utah
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The University of Utah is a public coeducational space-grant research university in Salt Lake City, Utah, United States. As the states flagship university, the university more than 100 undergraduate majors. The university is classified in the highest ranking, R-1, Doctoral Universities – Highest Research Activity by the Carnegie Classification of Institutions of Higher Education, the Carnegie Classification also considers the university as selective, which is its second most selective admissions category. Quinney College of Law and the School of Medicine, Utahs only medical school, as of Fall 2015, there are 23,909 undergraduate students and 7,764 graduate students, for an enrollment total of 31,673. The university was established in 1850 as the University of Deseret by the General Assembly of the provisional State of Deseret and it received its current name in 1892, four years before Utah attained statehood, and moved to its current location in 1900. The university ranks among the top 50 U. S. universities by total research expenditures with over $486 million spent in 2014, in addition, the universitys Honors College has been reviewed among 50 leading national Honors Colleges in the U. S. The university has also ranked the 12th most ideologically diverse university in the country. The universitys athletic teams, the Utes, participate in NCAA Division I athletics as a member of the Pac-12 Conference and its football team has received national attention for winning the 2005 Fiesta Bowl and the 2009 Sugar Bowl. A Board of Regents was organized by Brigham Young to establish a university in the Salt Lake Valley, early classes were held in private homes or wherever space could be found. The university closed in 1853 due to lack of funds and lack of feeder schools, the university moved out of the council house into the Union Academy building in 1876 and into Union Square in 1884. Additional Fort Douglas land has granted to the university over the years. Upon his death in 1900, Dr. John R. Park bequeathed his fortune to the university. One third of the faculty resigned in protest of these dismissals, the controversy was largely resolved when Kingsbury resigned in 1916, but university operations were again interrupted by World War I, and later The Great Depression and World War II. Student enrollment dropped to a low of 3,418 during the last year of World War II, ray Olpin made substantial additions to campus following the war, and enrollment reached 12,000 by the time he retired in 1964. Growth continued in the decades as the university developed into a research center for fields such as computer science. During the 2002 Winter Olympics, the university hosted the Olympic Village, the University of Utah Asia Campus opened as an international branch campus in the Incheon Global Campus in Songdo, Incheon, South Korea in 2014. Three other European and American universities are also participating, the Asia Campus was funded by the South Korean government. Campus takes up 1,534 acres, including the Health Sciences complex, Research Park and it is located on the east bench of the Salt Lake Valley, close to the Wasatch Range and approximately 2 miles east of downtown Salt Lake City
41.
Type Ia supernova
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A type Ia supernova is a type of supernova that occurs in binary systems in which one of the stars is a white dwarf. The other star can be anything from a giant star to a smaller white dwarf. Physically, carbon–oxygen white dwarfs with a low rate of rotation are limited to below 1.44 solar masses, beyond this, they re-ignite and in some cases trigger a supernova explosion. If a white dwarf accretes mass from a binary companion. If the white dwarf merges with another white dwarf, it will exceed the limit and begin to collapse. This type Ia category of supernovae produces consistent peak luminosity because of the mass of white dwarfs that explode via the accretion mechanism. In May 2015, NASA reported that the Kepler space observatory observed KSN 2011b, details of the pre-nova moments may help scientists better judge the quality of Type Ia supernovae as standard candles, which is an important link in the argument for dark energy. The Type Ia supernova is a sub-category in the Minkowski-Zwicky supernova classification scheme, there are several means by which a supernova of this type can form, but they share a common underlying mechanism. The current view among astronomers who model Type Ia supernova explosions, however, is that limit is never actually attained. At some point in this phase, a deflagration flame front is born. The details of the ignition are still unknown, including the location, oxygen fusion is initiated shortly thereafter, but this fuel is not consumed as completely as carbon. Once fusion has begun, the temperature of the white dwarf starts to rise, a main sequence star supported by thermal pressure would expand and cool which automatically counterbalances an increase in thermal energy. However, degeneracy pressure is independent of temperature, the dwarf is unable to regulate the fusion process in the manner of normal stars. The flame accelerates dramatically, in due to the Rayleigh–Taylor instability. It is still a matter of debate whether this flame transforms into a supersonic detonation from a subsonic deflagration. The star explodes violently and releases a wave in which matter is typically ejected at speeds on the order of 5, 000–20000 km/s. The energy released in the explosion causes an extreme increase in luminosity. The typical visual absolute magnitude of Type Ia supernovae is Mv = −19.3, the theory of this type of supernovae is similar to that of novae, in which a white dwarf accretes matter more slowly and does not approach the Chandrasekhar limit
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Type Ib and Ic supernovae
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Types Ib and Ic supernovae are categories of stellar explosions that are caused by the core collapse of massive stars. These stars have shed their outer envelope of hydrogen, and, compared to Type Ib, Type Ic supernovae are hypothesized to have lost more of their initial envelope, including most of their helium. The two types are referred to as stripped core-collapse supernovae. When a supernova is observed, it can be categorized in the Minkowski–Zwicky supernova classification scheme based upon the lines that appear in its spectrum. A supernova is first categorized as either a Type I or Type II, supernovae belonging to the general category Type I lack hydrogen lines in their spectra, in contrast to Type II supernovae which do display lines of hydrogen. The Type I category is sub-divided into Type Ia, Type Ib, Type Ib/Ic supernovae are distinguished from Type Ia by the lack of an absorption line of singly ionized silicon at a wavelength of 635.5 nanometres. As Type Ib/Ic supernovae age, they also display lines from elements such as oxygen, in contrast, Type Ia spectra become dominated by lines of iron. Type Ic supernovae are distinguished from Type Ib in that the former also lack lines of helium at 587.6 nm, prior to becoming a supernova, an evolved massive star is organized in the manner of an onion, with layers of different elements undergoing fusion. The outermost layer consists of hydrogen, followed by helium, carbon, oxygen, thus when the outer envelope of hydrogen is shed, this exposes the next layer that consists primarily of helium. This can occur when a hot, massive star reaches a point in its evolution when significant mass loss is occurring from its stellar wind. Highly massive stars can lose up to 10−5 solar masses each year—the equivalent of 1 M☉ every 100,000 years. In other respects, however, the mechanism behind Type Ib and Ic supernovae is similar to that of a Type II supernova. Because of their similarity, Type Ib and Ic supernovae are collectively called Type Ibc supernovae. However, it is hypothesized that any hydrogen-stripped Type Ib or Ic supernova could be a GRB. In any case, astronomers believe that most Type Ib, and probably Type Ic as well, result from core collapse in stripped, massive stars, rather than from the thermonuclear runaway of white dwarfs. As they are formed from rare, very massive stars, the rate of Type Ib and they normally occur in regions of new star formation, and have never been observed in an elliptical galaxy. Because they share a similar operating mechanism, Type Ib/c and the various Type II supernovae are collectively called core-collapse supernovae, in particular, Type Ib/c may be referred to as stripped core-collapse supernovae. The light curves of Type Ib supernovae vary in form, however, Type Ib light curves may peak at lower luminosity and may be redder
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Type II supernova
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A Type II supernova results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, and no more than 40–50 times and it is distinguished from other types of supernovae by the presence of hydrogen in its spectrum. Type II supernovae are mainly observed in the arms of galaxies and in H II regions. Stars generate energy by the fusion of elements. The star fuses increasingly higher mass elements, starting with hydrogen and then helium, progressing up through the table until a core of iron. Fusion of iron or nickel produces no net energy output, so no further fusion can take place, due to the lack of energy output creating outward pressure, equilibrium is broken and the core is compressed by the overlying mass of the star. When the compacted mass of the core exceeds the Chandrasekhar limit of about 1.4 M☉. A cataclysmic implosion of the takes place within seconds. Neutrons and neutrinos are formed via reversed beta-decay, releasing about 1046 joules in a ten-second burst, also, the collapse of the inner core is halted by neutron degeneracy, causing the implosion to rebound and bounce outward. The energy of this shock wave is sufficient to disrupt the overlying stellar material and accelerate it to escape velocity. Depending on initial size of the star, the remnants of the form a neutron star or a black hole. Because of the mechanism, the resulting nova is also described as a core-collapse supernova. There exist several categories of Type II supernova explosions, which are categorized based on the resulting light curve—a graph of luminosity versus time—following the explosion. Type II-L supernovae show a decline of the light curve following the explosion. Type Ib and Ic supernovae are a type of core-collapse supernova for a star that has shed its outer envelope of hydrogen. As a result, they appear to be lacking in these elements, stars far more massive than the sun evolve in more complex ways. The helium produced in the core accumulates there since temperatures in the core are not yet enough to cause it to fuse. Eventually, as the hydrogen at the core is exhausted, fusion starts to slow down and this contraction raises the temperature high enough to initiate a shorter phase of helium fusion, which accounts for less than 10% of the stars total lifetime
