Beyond the Limit

ESO/L. Calçada Illustration of a white dwarf with a strong magnetic field. In the 1930s, Subrahmanyan Chandrasekhar placed a limit on stars. Using our understanding of relativity and quantum theory, Chandrasekhar demonstrated that white dwarfs could never have a mass greater than 1.44 suns. It didn’t matter how they formed or whether they were mostly hydrogen or carbon. The very laws of physics forbid a greater mass. White dwarfs are the remains of smaller stars such as the Sun. When such a star runs out of fusable hydrogen, it swells to a red giant in a mad race to burn heavier elements. But without enough mass to achieve that reliably, the star soon collapses into a nuclear shell. Gravity wins the day, and the star can burn no more. Without nuclear pressure, the core collapses under its own weight until the quantum pressure of electrons can push back. The stable balance between gravity and electrons is what keeps the star from collapsing into a neutron star. Chandrasekhar was the…