Study Notes on Stellar Evolution

White Dwarfs: These are the remnants of low to medium-mass stars that have exhausted their nuclear fuel. They are incredibly dense, about the size of Earth but containing a mass similar to that of the Sun. Over billions of years, they cool down and fade, eventually becoming black dwarfs, theoretical remnants that have not yet been observed since the universe is not old enough for them to exist.

Neutron Stars: Formed from the gravitational collapse of high-mass stars (between $8$ and $25 M_{ ext{odot}}$) after a supernova explosion. They are incredibly dense, with protons and electrons fusing to form neutrons. Neutron stars can rotate extremely rapidly and exhibit strong magnetic fields, leading some to be classified as pulsars, which emit beams of radiation that can be detected when they sweep across Earth.

Black Holes: These are formed from the remnants of very high-mass stars (greater than $25 M_{ ext{odot}}$) that have undergone a supernova explosion. The core collapses under gravity to such an extent that not even light can escape from it, creating a region in spacetime with an event horizon. They were first theoretically predicted and later confirmed by astronomical observations in 1971. Black holes can be detected via their influence on nearby matter and the radiation emitted as matter falls into them.