In the 1960s, astronomers studying the formation and evolution of very-low-mass stars theorized the existence of a new class of objects, the brown dwarfs. Standard theory holds that stars form from the fragmentation and subsequent gravitational contraction of giant clouds of molecular gas and dust that permeate galaxies. As the fragmented clouds contract, gravitational potential energy is released as radiation and heat. That process raises the core temperature of the collapsing star, and if that temperature exceeds roughly 3 × 106 K, fusion reactions converting hydrogen into helium commence. Energy released by H fusion balances energy lost by radiation at the star’s surface, and pressure in the fusing core halts gravitational collapse. Hydrodynamic and thermal equilibria are established, and the long life of a normal star like the Sun begins.
The heating of a star’s core depends on the total gravitational energy released, which itself depends on the...
