A supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, consists of ejected material expanding from the explosion, the interstellar material it sweeps up and shocks along the way. There are two common routes to a supernova: either a massive star may run out of fuel, ceasing to generate fusion energy in its core, collapsing inward under the force of its own gravity to form a neutron star or a black hole. In either case, the resulting supernova explosion expels much or all of the stellar material with velocities as much as 10% the speed of light; these speeds are supersonic, so a strong shock wave forms ahead of the ejecta. That heats the upstream plasma up to temperatures well above millions of K; the shock continuously slows down over time as it sweeps up the ambient medium, but it can expand over hundreds or thousands of years and over tens of parsecs before its speed falls below the local sound speed.

One of the best observed young supernova remnants was formed by SN 1987A, a supernova in the Large Magellanic Cloud, observed in February 1987. Other well-known supernova remnants include the Crab Nebula; the youngest known remnant in our galaxy is G1.9+0.3, discovered in the galactic center. An SNR passes through the following stages as it expands: Free expansion of the ejecta, until they sweep up their own weight in circumstellar or interstellar medium; this can last tens to a few hundred years depending on the density of the surrounding gas. Sweeping up of a shell of shocked circumstellar and interstellar gas; this begins the Sedov-Taylor phase. Strong X-ray emission traces the strong shock waves and hot shocked gas. Cooling of the shell, to form a thin, dense shell surrounding the hot interior; this is the pressure-driven snowplow phase. The shell can be seen in optical emission from recombining ionized hydrogen and ionized oxygen atoms. Cooling of the interior; the dense shell continues to expand from its own momentum.

This stage is best seen in the radio emission from neutral hydrogen atoms. Merging with the surrounding interstellar medium; when the supernova remnant slows to the speed of the random velocities in the surrounding medium, after 30,000 years, it will merge into the general turbulent flow, contributing its remaining kinetic energy to the turbulence. There are three types of supernova remnant: Shell-like, such as Cassiopeia A Composite, in which a shell contains a central pulsar wind nebula, such as G11.2-0.3 or G21.5-0.9. Mixed-morphology remnants, in which central thermal X-ray emission is seen, enclosed by a radio shell; the thermal X-rays are from swept-up interstellar material, rather than supernova ejecta. Examples of this class include the SNRs W28 and W44. Remnants which could only be created by higher ejection energies than a standard supernova are called hypernova remnants, after the high-energy hypernova explosion, assumed to have created them. Supernova remnants are considered the major source of galactic cosmic rays.

The connection between cosmic rays and supernovas was first suggested by Walter Baade and Fritz Zwicky in 1934. Vitaly Ginzburg and Sergei Syrovatskii in 1964 remarked that if the efficiency of cosmic ray acceleration in supernova remnants is about 10 percent, the cosmic ray losses of the Milky Way are compensated; this hypothesis is supported by a specific mechanism called "shock wave acceleration" based on Enrico Fermi's ideas, still under development. Indeed, Enrico Fermi proposed in 1949 a model for the acceleration of cosmic rays through particle collisions with magnetic clouds in the interstellar medium; this process, known as the "Second Order Fermi Mechanism", increases particle energy during head-on collisions, resulting in a steady gain in energy. A model to produce Fermi Acceleration was generated by a powerful shock front moving through space. Particles that cross the front of the shock can gain significant increases in energy; this became known as the "First Order Fermi Mechanism".

Supernova remnants can provide the energetic shock fronts required to generate ultra-high energy cosmic rays. Observation of the SN 1006 remnant in the X-ray has shown synchrotron emission consistent with it being a source of cosmic rays. However, for energies higher than about 1018 eV a different mechanism is required as supernova remnants cannot provide sufficient energy, it is still unclear. The future telescope CTA will help to answer this question. List of All Known Galactic and Extragalactic Supernovae on the Open Supernova Catalog Galactic SNR Catalogue Chandra observations of supernova remnants: catalog, photo album, selected picks 2MASS images of Supernova Remnants NASA: Introduction to Supernova Remnants NASA's Imagine: Supernova Remnants Afterlife of a Supernova on UniverseToday.com Supernova remnant on arxiv.org Supernova Remnants, SEDS

Daniel B. Short is an American politician, he is a Republican member of the Delaware House of Representatives, representing District 39. He was elected in 2006 to replace retiring Republican Tina Fallon in the House, after having lost a race for the Delaware Senate in the previous election, he has served as the House Minority Leader since January 2013, was the minority whip. He served as a city council member and mayor of Seaford, Delaware, he earned an associate degree from the University of Delaware. In 2004, Short challenged incumbent Democrat Robert Venables Sr. for a seat in the Delaware Senate but lost the general election. In 2006, Short ran for a seat in the Delaware House and won the general election with 3,370 votes against Democratic nominee Richard Sternberg. In 2008, Short won the general election with 5,185 votes against Democratic nominee Jerry Semper, who had qualified and received votes as the Working Families Party candidate. In 2010, Short was unopposed for the general election.

In 2012, Short won the Republican primary with 1,046 votes, was unopposed for the general election, winning 6,191 votes. In 2014, Short won the general election with 3,977 votes against Libertarian nominee James W. Brittingham. In 2016, Short won the general election with 6,643 votes in a rematch against Libertarian nominee James W. Brittingham. In 2018, Short was unopposed in the general election. Official page at the Delaware General Assembly Campaign site Profile at Vote Smart

Robert Henderson is a Canadian politician, elected to the Legislative Assembly of Prince Edward Island in the 2007 provincial election. He is a member of the Liberal Party, he is the son of former MP George Henderson. In October 2011, Henderson was appointed to the Executive Council of Prince Edward Island as Minister of Tourism and Culture. Henderson continued to serve as Minister of Tourism when Wade MacLauchlan took over as premier in February 2015, but was left out when MacLauchlan shuffled the cabinet following the 2015 election. On January 7, 2016, Henderson returned to cabinet as Minister of Wellness. On January 10, 2018, Henderson was moved to Minister of Fisheries. Robert Henderson