What are Supernova Remnants?
A supernova remnant (usually abbreviated to SNR) is the remains of the matter that is exploded away from a star when it goes supernovae. This ejection of matter is much more violent than occurs in the planetary nebula that mark the end of a low mass star, giving expansion speeds of 1000-10,000 km s-1. The ejected matter sweeps up surrounding gas and dust as it expands producing a shock wave that excites and ionises the gas, which results in the production of X-rays, and radio waves in the form of synchrotron radiation. This plasma may reach temperatures of 1,000-1,000,000 K, but with densities of only about a million particles per cubic metre. Gradually, the expansion rate slows down, seeding the local neighbourhood with heavy elements, but not before the remnant occupies an area of space dozens or hundreds of light years in diameter.
