A supernova remnant is the expanding ejecta and shocked ambient medium left by a supernova explosion.
In the ideal cooled-shell limit with negligible continuing interior pressure, swept-up mass in a uniform medium scales as . Constant radial shell momentum then gives and . This differs from an energy-conserving blast wave or a pressure-driven snowplough.
A self-similar energy-conserving strong spherical explosion into a uniform ambient density has and . The dimensionless coefficient depends on the equation of state. Radiative losses, nonuniform media or continuous energy injection alter the similarity solution.
A monatomic strong shock has . Together with the Sedov-Taylor blast wave radius this gives . Extrapolating to ambient temperature or sonic speed estimates when the cold-upstream assumption fails, but the strong-shock law is already becoming inaccurate there. Radiative cooling can end the energy-conserving stage earlier; its transition age additionally needs a cooling function and composition.
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A supernova remnant is the structure resulting from the explosion of a star in a supernova event. When a massive star exhausts its nuclear fuel, it undergoes gravitational collapse followed by a catastrophic explosion, ejecting the outer layers of the star into space at high velocities. This explosion not only disperses a vast amount of stellar material, but it also generates intense shock waves that propagate through the surrounding interstellar medium.