Supernova Remnants
The intense radiation emitted by a supernova lasts from several months to a few years before fading away. In the meantime, the rapidly expanding (millions of miles per hour) matter from the explosion eventually crashes into circumstellar gas. This collision creates a supernova remnant consisting of hot gas and high-energy particles that glow in radio through X-ray wavelengths for thousands of years.
The process of forming the remnant is somewhat like an extreme version of sonic booms produced by the supersonic motion of an airplane. Expanding stellar debris creates a shock wave that races ahead of the debris. This forward shock wave produces sudden, large changes in pressure and temperature behind the shock wave.
The forward shock wave also accelerates electrons and other charged particles to extremely high energies. Electrons spiraling around the magnetic field behind the shock wave produce radiation over a wide range of wavelengths. Radiation from supernova remnants is especially conspicuous at radio wavelengths, and radio telescopes have traditionally been the primary tools for discovering these objects.
In recent years, supernova remnants have also been discovered with focusing X-ray telescopes. The X-rays are produced by the forward shock wave and by a reverse shock wave that heats the debris, or ejecta, of the exploded star. The reverse shock is formed as the high pressure gas behind the forward shock wave expands and pushes back on the stellar ejecta.
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