supernova

A supernova (SN) is a stellar explosion substantially more energetic than an ordinary nova. It is often briefly brighter than an entire galaxy, and fades away over a period of weeks or months. Energy emitted can be on the order of that of the Sun's entire lifetime. The explosion ejects most of the star's material at up to 10% of the speed of light, sweeping up interstellar gas and dust, which is called a supernova remnant. Classification regarding observable characteristics:

Type I - very little or no hydrogen:

• Type Ia - strong ionized silicon absorption lines.
• Type Ib - strong neutral helium spectral lines.
• Type Ic - also very little or no helium.

Type II - has hydrogen, broad emission lines:

• Type II-L - no narrow lines, constantly decreasing magnitude.
• Type II-P - no narrow lines, the decreasing light curve pauses in the midst of its decrease, remaining nearly constant for a period of time termed the light curve plateau.
• Type IIn - some narrow lines.
• Type IIb - eventually moves to Type Ib spectrum.

Type Ia supernovae are thought to consist of a white dwarf's fusion runaway (i.e., a thermonuclear supernova). The others are thought to be the core collapses of various types of large stars (core collapse supernovae).

The absolute brightness of a Type Ia supernova is thought to be determinable from its spectrum and fade time. These factors plus its apparent brightness are used to estimate distance to the supernova and thus to its galaxy and it can serve as a standard candle.

Devising reliable means to determine the absolute brightness of Type II supernova is of research interest. Factors discovered to correlate with the actual luminosity include the velocity of ejecta (determined through the spread of spectral lines associated with the ejecta) and color indices: heuristic use of these produces an absolute magnitude determination of useful accuracy. Some such methods determine the luminosity of a Type II-P supernova's plateau, which serves equally well as determining the peak luminosity.