A supernova (plural supernovae) is a stellar explosion which produces an extremely bright object made of plasma that declines to invisibility over weeks or months.
A supernova briefly outshines its entire host galaxy.
It would take 10 billion years for the Sun to produce the energy output of an ordinary Type II supernova.
Stars beneath the Chandrasekhar limit, such as the Sun, are too light to ever become supernovae and will evolve into white dwarfs.
There are several different types of supernovae and two possible routes to their formation.
A massive star may cease to generate fusion energy from fusing the nuclei of atoms in its core, and collapse under the force of its own gravity to form a neutron star or black hole.
Alternatively, a white dwarf star may accumulate material from a companion star until it nears its Chandrasekhar limit and undergoes runaway nuclear fusion in its interior, completely disrupting it.
This second type of supernova is distinct from a surface thermonuclear explosion on a white dwarf, which is called a nova.
In either type of supernova, the resulting explosion expels much or all of the stellar material with great force.