Rio de Janeiro
Rio de Janeiro, or Rio, is anchor to the Rio de Janeiro metropolitan area and the second-most populous municipality in Brazil and the sixth-most populous in the Americas. Rio de Janeiro is the capital of the state of Brazil's third-most populous state. Part of the city has been designated as a World Heritage Site, named "Rio de Janeiro: Carioca Landscapes between the Mountain and the Sea", by UNESCO on 1 July 2012 as a Cultural Landscape. Founded in 1565 by the Portuguese, the city was the seat of the Captaincy of Rio de Janeiro, a domain of the Portuguese Empire. In 1763, it became the capital of the State of Brazil, a state of the Portuguese Empire. In 1808, when the Portuguese Royal Court transferred itself from Portugal to Brazil, Rio de Janeiro became the chosen seat of the court of Queen Maria I of Portugal, who subsequently, in 1815, under the leadership of her son, the Prince Regent, future King João VI of Portugal, raised Brazil to the dignity of a kingdom, within the United Kingdom of Portugal and Algarves.
Rio stayed the capital of the pluricontinental Lusitanian monarchy until 1822, when the War of Brazilian Independence began. This is one of the few instances in history that the capital of a colonising country shifted to a city in one of its colonies. Rio de Janeiro subsequently served as the capital of the independent monarchy, the Empire of Brazil, until 1889, the capital of a republican Brazil until 1960 when the capital was transferred to Brasília. Rio de Janeiro has the second largest municipal GDP in the country, 30th largest in the world in 2008, estimated at about R$343 billion, it is headquarters to Brazilian oil and telecommunications companies, including two of the country's major corporations – Petrobras and Vale – and Latin America's largest telemedia conglomerate, Grupo Globo. The home of many universities and institutes, it is the second-largest center of research and development in Brazil, accounting for 17% of national scientific output according to 2005 data. Despite the high perception of crime, the city has a lower incidence of crime than Northeast Brazil, but it is far more criminalized than the south region of Brazil, considered the safest in the country.
Rio de Janeiro is one of the most visited cities in the Southern Hemisphere and is known for its natural settings, samba, bossa nova, balneario beaches such as Barra da Tijuca, Copacabana and Leblon. In addition to the beaches, some of the most famous landmarks include the giant statue of Christ the Redeemer atop Corcovado mountain, named one of the New Seven Wonders of the World. Rio de Janeiro was the host of the 2016 Summer Olympics and the 2016 Summer Paralympics, making the city the first South American and Portuguese-speaking city to host the events, the third time the Olympics were held in a Southern Hemisphere city; the Maracanã Stadium held the finals of the 1950 and 2014 FIFA World Cups, the 2013 FIFA Confederations Cup, the XV Pan American Games. Europeans first encountered Guanabara Bay on 1 January 1502, by a Portuguese expedition under explorer Gaspar de Lemos, captain of a ship in Pedro Álvares Cabral's fleet, or under Gonçalo Coelho; the Florentine explorer Amerigo Vespucci participated as observer at the invitation of King Manuel I in the same expedition.
The region of Rio was inhabited by the Tupi, Puri and Maxakalí peoples. In 1555, one of the islands of Guanabara Bay, now called Villegagnon Island, was occupied by 500 French colonists under the French admiral Nicolas Durand de Villegaignon. Villegagnon built Fort Coligny on the island when attempting to establish the France Antarctique colony; the city of Rio de Janeiro proper was founded by the Portuguese on 1 March 1565 and was named São Sebastião do Rio de Janeiro, in honour of St. Sebastian, the saint, the namesake and patron of the Portuguese then-monarch Sebastião. Rio de Janeiro was the name of Guanabara Bay; until early in the 18th century, the city was threatened or invaded by several French pirates and buccaneers, such as Jean-François Duclerc and René Duguay-Trouin. In the late 17th century, still during the Sugar Era, the Bandeirantes discovered gold and diamonds in the neighbouring captaincy of Minas Gerais, thus Rio de Janeiro became a much more practical port for exporting wealth than Salvador, much farther northeast.
On 27 January 1763, the colonial administration in Portuguese America was moved from Salvador to Rio de Janeiro. The city remained a colonial capital until 1808, when the Portuguese royal family and most of the associated Lisbon nobles, fleeing from Napoleon's invasion of Portugal, moved to Rio de Janeiro; the kingdom's capital was transferred to the city, thus, became the only European capital outside of Europe. As there was no physical space or urban structure to accommodate hundreds of noblemen who arrived many inhabitants were evicted from their homes. In the first decades, several educational establishments were created, such as the Military Academy, the Royal School of Sciences and Crafts and the Imperial Academy of Fine Arts, as well as the National Library of Brazil – with the largest collection in Latin America – and The Botanical Garden; the first printed newspaper in Brazil, the Gazeta do Rio de Janeiro, came into circulation during this period. When Brazil was elevated to Kingdom in 1815, it
In astronomy, the term "compact star" refers collectively to white dwarfs, neutron stars, black holes. It would grow to include exotic stars. Most compact stars are the endpoints of stellar evolution, thus referred to as stellar remnants, the form of the remnant depending on the mass of the star when it formed. All of these objects have a high mass relative to their radius, giving them a high density; the term compact star is used when the exact nature of the star is not known, but evidence suggests that it is massive and has a small radius, thus implying one of the above-mentioned categories. A compact star, not a black hole may be called a degenerate star; the usual endpoint of stellar evolution is the formation of a compact star. Most stars will come to a point in their evolution when the outward radiation pressure from the nuclear fusions in its interior can no longer resist the ever-present gravitational forces; when this happens, the star collapses under its own weight and undergoes the process of stellar death.
For most stars, this will result in the formation of a dense and compact stellar remnant known as a compact star. Compact stars have no internal energy production, but will—with the exception of black holes—usually radiate for millions of years with excess heat left from the collapse itself. According to the most recent understanding, compact stars could form during the phase separations of the early Universe following the Big Bang. Primordial origins of known compact objects have not been determined with certainty. Although compact stars may radiate, thus cool off and lose energy, they do not depend on high temperatures to maintain their structure, as ordinary stars do. Barring external disturbances and proton decay, they can persist forever. Black holes are however believed to evaporate from Hawking radiation after trillions of years. According to our current standard models of physical cosmology, all stars will evolve into cool and dark compact stars, by the time the Universe enters the so-called degenerate era in a distant future.
The somewhat wider definition of compact objects includes smaller solid objects such as planets and comets. There is a remarkable variety of stars and other clumps of hot matter, but all matter in the Universe must end as some form of compact stellar or substellar object, according to the theory of thermodynamics; the stars called white or degenerate dwarfs are made up of degenerate matter. White dwarfs arise from the cores of main-sequence stars and are therefore hot when they are formed; as they cool they will redden and dim until they become dark black dwarfs. White dwarfs were observed in the 19th century, but the high densities and pressures they contain were not explained until the 1920s; the equation of state for degenerate matter is "soft", meaning that adding more mass will result in a smaller object. Continuing to add mass to what is now a white dwarf, the object shrinks and the central density becomes larger, with higher degenerate-electron energies; the star's radius has now shrunk to only a few thousand kilometers, the mass is approaching the theoretical upper limit of the mass of a white dwarf, the Chandrasekhar limit, about 1.4 times the mass of the Sun.
If we were to take matter from the center of our white dwarf and start to compress it, we would first see electrons forced to combine with nuclei, changing their protons to neutrons by inverse beta decay. The equilibrium would shift towards heavier, neutron-richer nuclei that are not stable at everyday densities; as the density increases, these nuclei become less well-bound. At a critical density of about 4×1014 kg/m3), called the neutron drip line, the atomic nucleus would tend to fall apart into protons and neutrons. We would reach a point where the matter is on the order of the density of an atomic nucleus. At this point the matter is chiefly free neutrons, with a small amount of electrons. In certain binary stars containing a white dwarf, mass is transferred from the companion star onto the white dwarf pushing it over the Chandrasekhar limit. Electrons react with protons to form neutrons and thus no longer supply the necessary pressure to resist gravity, causing the star to collapse. If the center of the star is composed of carbon and oxygen such a gravitational collapse will ignite runaway fusion of the carbon and oxygen, resulting in a Type Ia supernova that blows apart the star before the collapse can become irreversible.
If the center is composed of magnesium or heavier elements, the collapse continues. As the density further increases, the remaining electrons react with the protons to form more neutrons; the collapse continues. A new equilibrium is possible after the star shrinks by three orders of magnitude, to a radius between 10 and 20 km; this is a neutron star. Although the first neutron star was not observed until 1967 when the first radio pulsar was discovered, neutron stars were proposed by Baade and Zwicky in 1933, only one year after the neutron was discovered in 1932, they realized that because neutron stars are so dense, the collapse of an ordinary star to a neutron star would liberate a large amount of gravitational potential energy, providing a possible explanation for supernovae. This is the explanation for supernovae of types Ib, Ic, II; such supernovae occur when the iron core of a massive star exceeds the Chandrasekhar limit and collapses to a neutron star. Li
Asteroseismology or astroseismology is the study of oscillations in stars. Because a star's different oscillation modes are sensitive to different parts of the star, they inform astronomers about the internal structure of the star, otherwise not directly possible from overall properties like brightness and surface temperature. Asteroseismology is related to helioseismology, the study of stellar oscillations in the Sun. Though both are based on the same underlying physics and qualitatively different information is available for the Sun because its surface can be resolved. By linearly perturbing the equations defining the mechanical equilibrium of a star and assuming that the perturbations are adiabatic, one can derive a system of four differential equations whose solutions give the frequency and structure of a star's modes of oscillation; the stellar structure is assumed to be spherically symmetric, so the horizontal component of the oscillations is described by spherical harmonics, indexed by an angular degree ℓ and azimuthal order m.
In non-rotating stars, modes with the same angular degree must all have the same frequency because there is no preferred axis. The angular degree indicates the number of nodal lines on the stellar surface, so for large values of ℓ, the opposing sectors cancel out, making it difficult to detect light variations; as a consequence, modes can only be detected up to an angular degree of about 3 in intensity and about 4 if observed in radial velocity. By additionally assuming that the perturbation to the gravitational potential is negligible and that the star's structure varies more with radius than the oscillation mode, the equations can be reduced to one second-order equation for the radial component of the displacement eigenfunction ξ r, d 2 ξ r d r 2 = ω 2 c s 2 ξ r where r is the radial co-ordinate in the star, ω is the angular frequency of the oscillation mode, c s is the sound speed inside the star, N is the Brunt-Vaisala or buoyancy frequency and S ℓ is the Lamb frequency; the last two are defined by N 2 = g and S ℓ 2 = ℓ c s 2 r 2 respectively.
By analogy with the behaviour of simple harmonic oscillators, this implies that oscillating solutions exist when the frequency is either greater or less than both S ℓ and N. We identify the former case as high-frequency pressure modes and the latter as low-frequency gravity modes; this basic separation allows us to determine where we expect what kind of mode to resonate in a star. By plotting the curves ω = N and ω = S ℓ, we expect p-modes to resonate at frequencies below both curves or frequencies above both curves. Κ -mechanism Under specific conditions, some stars have regions where heat is transported by radiation and the opacity is a decreasing function of temperature. This opacity bump can drive oscillations through the κ -mechanism. Suppose that, at the beginning of an oscillation cycle, the stellar envelope has contracted. By expanding and cooling the layer in the opacity bump becomes more opaque, absorbs more radiation, heats up; this heating causes expansion, further cooling and the layer becomes more opaque.
This continues until the material opacity stops increasing so at which point the radiation trapped in the layer can escape. The star contracts and the cycle prepares to commence again. In this sense, the opacity acts like a valve. Pulsations driven by the κ -mechanism are coh
Gamma-ray burst progenitors
Gamma-ray burst progenitors are the types of celestial objects that can emit gamma-ray bursts. GRBs show an extraordinary degree of diversity, they can last anywhere from a fraction of a second to many minutes. Bursts could have a single profile or oscillate wildly up and down in intensity, their spectra are variable unlike other objects in space; the near complete lack of observational constraint led to a profusion of theories, including evaporating black holes, magnetic flares on white dwarfs, accretion of matter onto neutron stars, antimatter accretion, supernovae and rapid extraction of rotational energy from supermassive black holes, among others. There are at least two different types of progenitors of GRBs: one responsible for the long-duration, soft-spectrum bursts and one responsible for short-duration, hard-spectrum bursts; the progenitors of long GRBs are believed to be massive, low-metallicity stars exploding due to the collapse of their cores. The progenitors of short GRBs are thought to arise from mergers of compact binary systems like neutron stars, confirmed by the GW170817 observation of a neutron star merger and a kilonova.
As of 2007, there is universal agreement in the astrophysics community that the long-duration bursts are associated with the deaths of massive stars in a specific kind of supernova-like event referred to as a collapsar or hypernova. Massive stars are able to fuse material in their centers all the way to iron, at which point a star cannot continue to generate energy by fusion and collapses, in this case forming a black hole. Matter from the star around the core rains down towards the center and swirls into a high-density accretion disk; the infall of this material into the black hole drives a pair of jets out along the rotational axis, where the matter density is much lower than in the accretion disk, towards the poles of the star at velocities approaching the speed of light, creating a relativistic shock wave at the front. If the star is not surrounded by a thick, diffuse hydrogen envelope, the jets' material can pummel all the way to the stellar surface; the leading shock accelerates as the density of the stellar matter it travels through decreases, by the time it reaches the surface of the star it may be traveling with a Lorentz factor of 100 or higher.
Once it reaches the surface, the shock wave breaks out into space, with much of its energy released in the form of gamma-rays. Three special conditions are required for a star to evolve all the way to a gamma-ray burst under this theory: the star must be massive to form a central black hole in the first place, the star must be rotating to develop an accretion torus capable of launching jets, the star must have low metallicity in order to strip off its hydrogen envelope so the jets can reach the surface; as a result, gamma-ray bursts are far rarer than ordinary core-collapse supernovae, which only require that the star be massive enough to fuse all the way to iron. This consensus is based on two lines of evidence. First, long gamma-ray bursts are found without exception in systems with abundant recent star formation, such as in irregular galaxies and in the arms of spiral galaxies; this is strong evidence of a link to massive stars, which evolve and die within a few hundred million years and are never found in regions where star formation has long ceased.
This does not prove the collapsar model but does provide significant support. Second, there are now several observed cases where a supernova has followed a gamma-ray burst. While most GRBs occur too far away for current instruments to have any chance of detecting the faint emission from a supernova at that distance, for lower-redshift systems there are several well-documented cases where a GRB was followed within a few days by the appearance of a supernova; these supernovae that have been classified are type Ib/c, a rare class of supernova caused by core collapse. Type Ib and Ic supernovae lack hydrogen absorption lines, consistent with the theoretical prediction of stars that have lost their hydrogen envelope; the GRBs with the most obvious supernova signatures include GRB 060218, GRB 030329, GRB 980425, a handful of more distant GRBs show supernova "bumps" in their afterglow light curves at late times. Possible challenges to this theory emerged with the discovery of two nearby long gamma-ray bursts that lacked the signature of any type of supernova: both GRB060614 and GRB 060505 defied predictions that a supernova would emerge despite intense scrutiny from ground-based telescopes.
Both events were, associated with star-forming stellar populations. One possible explanation is that during the core collapse of a massive star a black hole can form, which then'swallows' the entire star before the supernova blast can reach the surface. Short gamma-ray bursts appear to be an exception; until 2007, only a handful of these events have been localized to a definite galactic host. However, those that have been localized appear to show significant differences from the long-burst population. While at least one short burst has been found in the star-forming central region of a galaxy, several others have been associated with the outer regions and the outer halo of large elliptical galaxies in which star formation has nearly ceased. All the hosts identified so far have been at low redshift. Furthermore, despite the nearby distances and detailed follow-up study for these ev
A pulsar is a magnetized rotating neutron star that emits a beam of electromagnetic radiation. This radiation can be observed only when the beam of emission is pointing toward Earth, is responsible for the pulsed appearance of emission. Neutron stars are dense, have short, regular rotational periods; this produces a precise interval between pulses that ranges from milliseconds to seconds for an individual pulsar. Pulsars are believed to be one of the candidates for the source of ultra-high-energy cosmic rays; the periods of pulsars make them 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 1967, by Jocelyn Bell Burnell and Antony Hewish. They observed pulses separated by 1.33 seconds that originated from the same location in the sky, kept to sidereal time.
In looking for explanations for the pulses, the short period of the pulses eliminated most astrophysical sources of radiation, such as stars, since the pulses followed sidereal time, it could not be man-made radio frequency interference. When observations with another telescope confirmed the emission, it eliminated any sort of instrumental effects. At this point, Bell Burnell said of herself and Hewish that "we did not believe that we had picked up signals from another civilization, but the idea had crossed our minds and we had no proof that it was an natural radio emission, it is an interesting problem—if one thinks one may have detected life elsewhere in the universe, how does one announce the results responsibly?" So, they nicknamed the signal LGM-1, for "little green men". It was not until a second pulsating source was discovered in a different part of the sky that the "LGM hypothesis" was abandoned, their pulsar was dubbed CP 1919, is now known by a number of designators including PSR 1919+21 and PSR J1921+2153.
Although CP 1919 emits in radio wavelengths, pulsars have subsequently been found to emit in visible light, X-ray, gamma ray wavelengths. The word "pulsar" is a portmanteau of'pulsating' and'quasar', first appeared in print in 1968: The existence of neutron stars was first proposed by Walter Baade and Fritz Zwicky in 1934, when they argued that a small, dense star consisting of neutrons would result from a supernova. Based on the idea of magnetic flux conservation from magnetic main sequence stars, Lodewijk Woltjer proposed in 1964 that such neutron stars might contain magnetic fields as large as 10^14 to 10^16 G. In 1967, shortly before the discovery of pulsars, Franco Pacini suggested that a rotating neutron star with a magnetic field would emit radiation, noted that such energy could be pumped into a supernova remnant around a neutron star, such as the Crab Nebula. After the discovery of the first pulsar, Thomas Gold independently suggested a rotating neutron star model similar to that of Pacini, explicitly argued that this model could explain the pulsed radiation observed by Bell Burnell and Hewish.
The discovery of the Crab pulsar in 1968 seemed to provide confirmation of the rotating neutron star model of pulsars. The Crab pulsar has a 33-millisecond pulse period, 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. In 1974, Antony Hewish and Martin Ryle became the first astronomers to be awarded the Nobel Prize in Physics, with the Royal Swedish Academy of Sciences noting that Hewish played a "decisive role in the discovery of pulsars". Considerable controversy is associated with the fact that Hewish was awarded the prize while Bell, who made the initial discovery while she was his PhD student, was not. Bell claims no bitterness upon this point. In 1974, Joseph Hooton Taylor, Jr. and Russell Hulse discovered for the first time a pulsar in a binary system, PSR B1913+16. This pulsar orbits another neutron star with an orbital period of just eight hours.
Einstein's theory of general relativity predicts that this system should emit strong gravitational radiation, causing the orbit to continually contract as it loses orbital energy. Observations of the pulsar soon confirmed this prediction, providing the first evidence of the existence of gravitational waves; as of 2010, observations of this pulsar continue to agree with general relativity. In 1993, the Nobel Prize in Physics was awarded to Taylor and Hulse for the discovery of this pulsar. In 1982, Don Backer led a group which discovered PSR B1937+21, a pulsar with a rotation period of just 1.6 milliseconds. Observations soon revealed that its magnetic field was much weaker than ordinary pulsars, while further discoveries cemented the idea that a new class of object, the "millisecond pulsars" had been found. MSPs are believed to be the end product of X-ray binaries. Owing to their extraordinarily rapid and stable rotation, MSPs can be used by astronomers as clocks rivaling the stability of the best atomic clocks on Earth.
Factors affecting the arrival time of pulses at Earth by more than a few hundred nanoseconds can be detected and used to make precise measurements. Physical parameters accessible through pulsar timing include the 3D p
Asteroseismology studies the internal structure of our Sun and other stars using oscillations. These can be studied by interpreting the temporal frequency spectrum acquired through observations. In the same way, the more extreme neutron stars might be studied and give us a better understanding of neutron-star interiors, help in determining the equation of state for matter at nuclear densities. Scientists hope to prove, or discard, the existence of so-called quark stars, or strange stars, through these studies; the modes of oscillations are divided into each with different characteristic behavior. First they are divided into toroidal and spherical modes, with the latter further divided into radial and non-radial modes. Spherical modes are oscillations in the radial direction while toroidal modes oscillate horizontally, perpendicular to the radial direction; the radial modes can be considered as a special case of non-radial ones, preserving the shape of the star in the oscillations, while the non-radial do not.
Only the spherical modes are considered in studies of stars, as they are the easiest to observe, but the toroidal modes might be studied. In our Sun, only three types of modes have been found g - and f - modes. Helioseismology studies these modes with periods in the range of minutes, while for neutron stars the periods are much shorter seconds or milliseconds. P-modes or pressure modes, are determined by the local sound speed in the star, hence they are often referred to as acoustic modes. Dependent on the density and temperature of the neutron star, they are powered by internal pressure fluctuations in the stellar medium. Typical predicted periods lie around 0.1 ms. g-modes or gravity modes, have buoyancy as restoring force, but should not be confused with gravitational waves. The g-modes are confined to the inner regions of a neutron star with a solid crust, have predicted oscillation periods between 10 and 400 ms. However, there are expected long-period g-modes oscillating on periods longer than 10 s. f-modes or fundamental modes, are g-modes confined to the surface of the neutron star, similar to ripples in a pond.
Predicted periods are between 0.1 and 0.8 ms. The extreme properties of neutron stars permit several others types of modes. S-modes or shear modes, appear in two cases. In the crust they depend on the crust's shear modulus. Predicted periods range between a few milliseconds to tens of seconds. I-modes or interfacial modes, appear at the boundaries of the different layers of the neutron star, causing traveling waves with periods dependent on the local density and temperature at the interface. Typical predicted. T-modes or torsional modes, are caused by material motions tangentially to the surface in the crust. Predicted periods are shorter than 20 ms. r-modes or Rossby modes only appear in rotating stars and are caused by the Coriolis force acting as restoring force along the surface. Their periods are on the same order as the star's rotation. A phenomenological description could be found in w-modes or gravitational-wave modes are a relativistic effect, dissipating energy through gravitational waves.
Their existence was first suggested through a simple model problem by Kokkotas and Schutz and verified numerically by Kojima, whose results were corrected and extended by Kokkotas and Schutz. Characteristic properties of these modes are the absence of any significant fluid motion and their rapid damping times of tenths of seconds. There are three types of w-mode oscillations: curvature and interface modes, with predicted periods in the range of microseconds. Trapped modes would exist in compact stars, their existence was suggested by Chandrasekhar and Ferrari, but so far no realistic Equation of State has been found allowing the formation of stars compact enough to support these modes. Curvature modes are related to the spacetime curvature. Models and numerical studies suggest an unlimited number of these modes. Interface modes or wII-modes are somewhat similar to acoustic waves scattered off a hard sphere, they are damped in less than a tenth of a millisecond, so would be hard to observe. More details on stellar pulsation modes and a comparison with the pulsation modes of black holes can be found in the Living Review by Kokkotas and Schmidt.
Oscillations are caused when a system is perturbed from its dynamical equilibrium, the system, using a restoration force, tries to return to that equilibrium state. The oscillations in neutron stars are weak with small amplitudes, but exciting these oscillations might increase the amplitudes to observable levels. One of the general excitation mechanisms are eagerly awaited outbursts, comparable to how one creates a tone when hitting a bell; the hit adds energy to the system, which excites the amplitudes of the oscillations to greater magnitude, so is more observed. Apart from such outbursts, flares as they are called, other mechanisms have been proposed to contribute to these excitations: The core collapse during a supernova which produces a neutron star is one good candidate as it releases enormous amounts of energy. For a binary system with at least one neutron star, the accretion process as matter flows into the star might be a source of moderately high energy. Gravitational radiation is released as the components in a binary systems spiral closer to each other, releasing energy which might be energetic enough for visible excitations.
So called sudden phase transition during transitions to, e.g. a strange st
A magnetar is a type of neutron star believed to have an powerful magnetic field. The magnetic field decay powers the emission of high-energy electromagnetic radiation X-rays and gamma rays; the theory regarding these objects was proposed by Robert Duncan and Christopher Thompson in 1992, but the first recorded burst of gamma rays thought to have been from a magnetar had been detected on March 5, 1979. During the following decade, the magnetar hypothesis became accepted as a explanation for soft gamma repeaters and anomalous X-ray pulsars. Like other neutron stars, magnetars are around 20 kilometres in diameter and have a mass 2–3 times that of the Sun; the density of the interior of a magnetar is such that a tablespoon of its substance would have a mass of over 100 million tons. Magnetars are differentiated from other neutron stars by having stronger magnetic fields, by rotating comparatively quicker. Most neutron stars rotate once every one to ten seconds, whereas magnetars rotate once in less than one second.
A magnetar's magnetic field gives rise to strong and characteristic bursts of X-rays and gamma rays. The active life of a magnetar is short, their strong magnetic fields decay after about 10,000 years, after which activity and strong X-ray emission cease. Given the number of magnetars observable today, one estimate puts the number of inactive magnetars in the Milky Way at 30 million or more. Starquakes triggered on the surface of the magnetar disturb the magnetic field which encompasses it leading to powerful gamma ray flare emissions which have been recorded on Earth in 1979, 1998, 2004. Magnetars are characterized by their powerful magnetic fields of 108 to 1011 tesla; these magnetic fields are hundreds of millions of times stronger than any man-made magnet, quadrillions of times more powerful than the field surrounding Earth. Earth has a geomagnetic field of 30–60 microteslas, a neodymium-based, rare-earth magnet has a field of about 1.25 tesla, with a magnetic energy density of 4.0×105 J/m3.
A magnetar's 1010 tesla field, by contrast, has an energy density of 4.0×1025 J/m3, with an E/c2 mass density more than 10,000 times that of lead. The magnetic field of a magnetar would be lethal at a distance of 1000 km due to the strong magnetic field distorting the electron clouds of the subject's constituent atoms, rendering the chemistry of life impossible. At a distance of halfway from Earth to the moon, a magnetar could strip information from the magnetic stripes of all credit cards on Earth; as of 2010, they are the most powerful magnetic objects detected throughout the universe. As described in the February 2003 Scientific American cover story, remarkable things happen within a magnetic field of magnetar strength. "X-ray photons split in two or merge. The vacuum itself is polarized, becoming birefringent, like a calcite crystal. Atoms are deformed into long cylinders thinner than the quantum-relativistic de Broglie wavelength of an electron." In a field of about 105 teslas atomic orbitals deform into rod shapes.
At 1010 teslas, a hydrogen atom becomes a spindle 200 times narrower than its normal diameter. The strong fields of magnetars are understood as resulting from a magnetohydrodynamic dynamo process in the turbulent dense conducting fluid that exists before the neutron star settles into its equilibrium configuration; these fields persist due to persistent currents in a proton-superconductor phase of matter that exists at an intermediate depth within the neutron star. A similar magnetohydrodynamic dynamo process produces more intense transient fields during coalescence of pairs of neutron stars; when in a supernova, a star collapses to a neutron star, its magnetic field increases in strength. Halving a linear dimension increases the magnetic field fourfold. Duncan and Thompson calculated that when the spin and magnetic field of a newly formed neutron star falls into the right ranges, a dynamo mechanism could act, converting heat and rotational energy into magnetic energy and increasing the magnetic field an enormous 108 teslas, to more than 1011 teslas.
The result is a magnetar. It is estimated that about one in ten supernova explosions results in a magnetar rather than a more standard neutron star or pulsar. On March 5, 1979, a few months after the successful dropping of satellites into the atmosphere of Venus, the two unmanned Soviet spaceprobes, Venera 11 and 12, that were drifting through the Solar System were hit by a blast of gamma radiation at 10:51 EST; this contact raised the radiation readings on both the probes from a normal 100 counts per second to over 200,000 counts a second, in only a fraction of a millisecond. This burst of gamma rays continued to spread. Eleven seconds Helios 2, a NASA probe, in orbit around the Sun, was saturated by the blast of radiation, it soon hit Venus, the Pioneer Venus Orbiter's detectors were overcome by the wave. Seconds Earth received the wave of radiation, where the powerful output of gamma rays inundated the detectors of three U. S. Department of Defense Vela satellites, the Soviet Prognoz 7 satellite, the Einstein Observatory.
Just before the wave exited the Solar System, the blast hit the International Sun–Earth Explorer. This powerful blast of gamma radiation constituted the strongest wave of extra-solar gamma rays detected; because gamma rays travel at the speed of light and the time of the pulse