BRAINCAKEWhite Dwarfs and the Chandrasekhar Limit
A white dwarf is the hot, dense remnant core of a low-mass star. It has a mass similar to the Sun's but a radius similar to the Earth's, so its density is enormous, about 109 kg m−3. No fusion takes place in it. It is white-hot at first and glows only because of the thermal energy it still has, so it slowly cools and dims.
What stops a white dwarf collapsing under its own gravity? Its electrons are squeezed so close together that a quantum effect called electron degeneracy pressure acts. The Pauli exclusion principle says that no two electrons can occupy the same quantum state, so the electrons resist being squeezed into a smaller space. This produces an outward pressure that balances gravity.
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