A supernova remnant is a possible after-effect of a supernova, essentially a type of nebula. It consisting of the supernova's ejected debris (material ejected from the exploding star, often at relativistic speeds), along with interstellar medium affected by the debris. The remnant may be optically visible if a source of light is nearby that is reflected, or if the debris collision with other material causes one or both to heat from the shock. The aftermath of a supernova (the beginning of its life as a remnant) is modeled as passing through three phases:
Example supernova remnants:
A different term, stellar remnant, is used for a black hole or neutron star left from a supernova. These remain after any supernova remnant has dissipated.
A nova remnant is the analogous debris sometimes produced by a nova, which is typically a flash triggered by accretion onto a white dwarf. A nova remnant is smaller, slower, and fades faster than a supernova remnant, but may leave a brighter central star to illuminate it.