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Supernova (Type Ia and Type II)
Two unrelated ways for a star to explode, useful for two entirely different reasons.
A Type II supernova is a massive star running out of fuel: the core collapses in about a second, and the rebound blows the rest of the star apart, leaving a neutron star or a black hole. A Type Ia is a white dwarf in a binary system stealing matter from its companion until it crosses a mass limit and detonates completely, leaving nothing. The distinction matters beyond bookkeeping: because Type Ia explosions all happen at nearly the same mass, they all reach nearly the same brightness, which makes them measuring sticks. Comparing how bright they look to how bright they must be is how the accelerating expansion of the universe was found.
Where it has come up lately
Related terms
Magnetar
A neutron star with a magnetic field a thousand trillion times Earth's.
The main sequence
The long, stable middle age a star spends fusing hydrogen in its core.
Hertzsprung–Russell diagram
The single plot that organises everything about stars.
Red giant
What a star becomes when the hydrogen in its core runs out.
Questions
What is Supernova (Type Ia and Type II)?
Two unrelated ways for a star to explode, useful for two entirely different reasons.
Why does it matter?
The distinction matters beyond bookkeeping: because Type Ia explosions all happen at nearly the same mass, they all reach nearly the same brightness, which makes them measuring sticks. Comparing how bright they look to how bright they must be is how the accelerating expansion of the universe was found.