Kanishka NaikA supernova remnant (SNR) is the structure remaining after a star explodes as a supernova. It consists of ejected stellar material and an expanding shock wave that sweeps up and heats surrounding interstellar gas.
SNRs pass through distinct evolutionary stages: free expansion of ejecta lasting decades to centuries, the Sedov-Taylor phase where a shell of shocked gas is swept up, and finally merging with the interstellar medium after roughly 30,000 years when expansion slows to ambient velocities.
SNRs enrich galaxies with heavy elements and accelerate particles to near-light speed via shock waves, making them a major confirmed source of galactic cosmic rays. This was first proposed by Baade and Zwicky in 1934 and is supported by synchrotron X-ray observations.