supernova remnant

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:

• free expansion phase (little difference from expansion into a perfect vacuum).
• Sedov-Taylor phase (basically an adiabatic process).
• snowplow phase - (gathers ISM and cools through emitted EMR).

Example supernova remnants:

• Crab Nebula (M1).
• Cassiopeia A.
• Remnant of SN 1987A.

Some classification:

• shell-type remnants - like Cas A, appearing as circles in the sky, the appearance of EMR emitted by a shell-shaped volume surrounding the supernova location, the EMR resulting from the shock of debris meeting ISM.
• crab-type remnants - like the Crab Nebula, with substantial EMR from closer to the supernova location, a result of a central pulsar.
• composite remnants - showing characteristics of both.

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.