A burnt-out star — a white dwarf — holds itself up not with heat but with a quantum stubbornness of its electrons. But that stubbornness has a limit: pile on more than about 1.4 times the Sun’s mass and even the electrons give way, and the star collapses catastrophically — a supernova, leaving a neutron star or black hole. Chandrasekhar found this at 19. Slide the mass past the edge.
A white dwarf is supported against gravity by ELECTRON DEGENERACY PRESSURE — the Pauli exclusion principle forcing electrons apart even at zero temperature. But as mass rises the electrons must move at relativistic speeds, and their pressure grows too slowly to keep up with gravity: above the Chandrasekhar limit, M ≈ 1.44 solar masses, no equilibrium exists and the star collapses — igniting a Type Ia supernova (a white dwarf accreting past the limit) or forming a neutron star. Because the limit is nearly universal, Type Ia supernovae are ‘standard candles’ for cosmic distance. A fail-loud self-check throws unless masses below ~1.44 are stable and above it collapse. ◆ real astrophysics, node-verified.
The classic ~1.44 M☉ limit (exact for a non-rotating, standard-composition dwarf; rotation and magnetic fields shift it slightly); the standard-candle use underpins the dark-energy discovery — the electron-degeneracy ceiling is exact.