Supernova remnant

A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave. It consists of ejected material expanding from the explosion, and 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, and collapsing inward under the force of its own gravity to form a neutron star or a black hole; or a white dwarf star may accrete material from a companion star until it reaches a critical mass and undergoes a carbon detonation. 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 (or approximately 30,000 km/s) and 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 as it sweeps up the ambient medium, but it can expand over hundreds or thousands of years and 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; Tycho, the remnant of SN 1572, named after Tycho Brahe, who recorded the brightness of its original explosion; and Kepler, the remnant of SN 1604, named after Johannes Kepler. The youngest known remnant in the Milky Way is G1.9+0.3, discovered in the Galactic Center.