Before becoming "the father of the atom bomb," J. Robert Oppenheimer made a significant contribution to the science of black holes.
Oppenheimer will forever, for better or for worse, be associated with the incredible destructive power of the atomic bomb and the image of the mushroom cloud, a near-Biblical symbol of destruction. That association will only strengthen in the public eye with today's (July 21) release of "Oppenheimer," Christopher Nolan's highly anticipated biopic about the physicist.
But before journeying to Los Alamos, New Mexico, in 1942 to contribute to the development of the atomic bomb, Oppenheimer was a theoretical physicist focusing on quantum physics. In 1939, he and his University of California, Berkeley colleague Hartland S. Snyder published a pioneering paper entitled "On Continued Gravitational Contraction," which used the equations of Albert Einstein's theory of gravity, general relativity, to show how black holes could be born.
"Oppenheimer proposed the very first collapse model to describe how a star could collapse into a black hole," Xavier Calmet, a professor of physics at the University of Sussex in England, told Space.com. "This model explains the formation of black holes as a dynamical astrophysical process, the final stage of the evolution of heavy-enough stars. This model is still being used today."
Calmet said that he recently used the model himself, in a paper describing the collapse of black holes when considering quantum gravity.
"This model is very significant because it is analytically solvable — solving the equations can be done with pen and paper and does not require numerical work. All the physics is thus easily trackable," he said. "Yet, despite its simplicity and maybe even crudeness, it is complex enough to describe many of the features of a collapsing star."
Ironically, as Oppenheimer and Snyder worked on the paper, which so heavily depended on the 1915 theory of general relativity, the father of that theory, Einsten, was himself completing research aimed at showing that black holes could not exist.
History would show Oppenheimer to be right about black holes, of course.
Oppenheimer pushes the limit
Eight years before Oppenheimer's theory of star collapse and black hole birth, another theoretical physicist was thinking about what happens when stars run out of fuel for nuclear fusion.
When this fuel is exhausted, a star can no longer support itself against gravitational collapse. While the star's outer layers are shed, its core rapidly contracts, leaving an exotic stellar remnant. The nature of the remnant depends on the mass of the stellar core.
Indian-American physicist Subrahmanyan Chandrasekhar realized that, for stellar cores with a mass less than 1.4 times that of the sun, gravitational collapse would halt due to quantum effects that prevent particles from "squashing" too close together.
This would come to be known as the Chandrasekhar limit, and any star below it — unless it has a stellar companion feeding it material — is doomed to end its existence as a smoldering stellar remnant called a white dwarf. That will be the fate of our star, the sun, after it exhausts the hydrogen at its core in around 5 billion years.
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