Final answer:
Electron degeneracy is a quantum mechanical effect that holds up a white dwarf against the force of gravity by providing degeneracy pressure from the electrons, as they cannot occupy the same quantum state, preventing the star from collapsing further.
Step-by-step explanation:
Electron degeneracy is what holds up a white dwarf against the compressing force of gravity. As a white dwarf forms during stellar evolution, the atomic nuclei and the electrons within the core get squeezed to high densities. However, it is the electrons that reach a point of degeneracy first, where further compression would violate the Pauli exclusion principle. This principle, a fundamental rule of quantum physics, states that no two electrons can occupy the same quantum state at the same time. The degenerate electrons exert a repulsive force, creating a degeneracy pressure that halts the collapse of the core. Therefore, this degeneracy pressure is what supports the star against gravity, preventing it from further collapse. This is part of what was eloquently described by Subrahmanyan Chandrasekhar in his calculations that defined the characteristics of white dwarfs, including their final size and mass limit, known as the Chandrasekhar limit.