White 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.Electron degeneracy pressure has a limit. The Chandrasekhar limit is the maximum mass of a stable white dwarf:Chandrasekhar limit ≈ 1.44 M_☉ (1.44 solar masses)If the mass of a stellar core is less than 1.44 solar masses, electron degeneracy pressure can support it, and it becomes a white dwarf.If the core's mass is greater than 1.44 solar masses, electron degeneracy pressure cannot prevent gravitational collapse. The core collapses further, forming a neutron star or a black hole.Example: a remnant core of 1.2 solar masses is below the limit, so it will form a white dwarf. A remnant core of 2.0 solar masses is above the limit, so it cannot become a white dwarf.