What prevents a white dwarf from collapsing under its own weight?

A white dwarf is prevented from collapsing under its own weight by electron degeneracy pressure, a quantum mechanical effect arising from the Pauli exclusion principle. In a white dwarf, electrons are packed closely together, and this degeneracy pressure provides a counterforce to the gravitational pull trying to compress the star further. As long as the mass of the white dwarf remains below the Chandrasekhar limit (approximately 1.4 solar masses), this balance is maintained, allowing the white dwarf to remain stable.