A Teenage Discovery
In 1930, nineteen-year-old Subrahmanyan Chandrasekhar, sailing from India to Cambridge, combined quantum mechanics with special relativity to derive a stunning result: white dwarf stars have a maximum possible mass. Above approximately 1.4 solar masses, the quantum pressure of degenerate electrons — the very force that supports white dwarfs — becomes insufficient against gravity. This discovery, initially met with fierce opposition from Arthur Eddington, eventually earned Chandrasekhar the 1983 Nobel Prize.
Electron Degeneracy Pressure
In a white dwarf, electrons are packed so tightly that quantum mechanics forbids them from occupying the same state (the Pauli exclusion principle). This creates an outward 'degeneracy pressure' independent of temperature. However, as the white dwarf mass increases, electrons are forced to higher momenta, approaching the speed of light. In this ultra-relativistic limit, the pressure equation of state softens from ρ^(5/3) to ρ^(4/3), and a maximum supportable mass emerges.
The Mass-Radius Paradox
Unlike normal stars, white dwarfs get smaller as they gain mass — the mass-radius relation runs backwards. Adding mass increases gravity, compressing the star further. Near the Chandrasekhar limit, the radius shrinks dramatically toward zero while central density soars toward infinity. This simulation visualizes this counterintuitive relationship and shows how the white dwarf structure changes as mass approaches the critical threshold.
Type Ia Supernovae
When a white dwarf in a binary system accretes matter from a companion star and approaches the Chandrasekhar limit, carbon ignites in the degenerate core. Unlike in a normal star where the gas would expand and cool, the degenerate material cannot expand — fusion runs away catastrophically, incinerating the entire white dwarf in a Type Ia supernova. These explosions synthesize about 0.6 M☉ of radioactive nickel-56 and serve as cosmological standard candles that revealed the accelerating expansion of the universe.