The suggestion that stars were giant machines for releasing vast amounts of energy by turning hydrogen into helium triggered a burst of discoveries and wild new theories. Breakthroughs in the study of atomic physics on Earth proved to have implications for the nature and structure of some exotic stars. For example, astronomers had known for some time of the existence of superdense white dwarfs, but it was in 1927 that Indian astronomer Subramanyan Chandrasekhar (1910— 1995) suggested that they might be the collapsed cores of burned-out stars, supported only by the pressure between their atoms. In 1932, Russian physicist Lev Landau realized that atomic physics put an upper limit on the mass of white dwarfs. Above a certain weight, known as the Chandrasekhar limit, the forces between the particles in the star would not be able to resist gravity, and the stellar remnant would collapse to an even denser state, a neutron star. Such stars were finally detected with the discovery of the first pulsar (see p.67) in 1967. And even neutron stars proved to have an upper limit, above which their particles would dissolve into even tinier quarks and they would collapse to form black holes.
Best known for his book A Brief History of Time, Stephen Hawking did much of his groundbreaking work in the 1960s and 1970s on the structure of black holes. Such objects, whose gravity stops light from escaping from them, had first been suggested in the 18th century, but were revived by the discoveries of particle physics in the 1960s. Hawking discovered many aspects of black hole behavior, most famously the "Hawking radiation" that is generated around their boundaries.
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