Soviet physicist Lev Landau ventured into stellar theory three times during his twenties. In 1931 a hope of turning up fundamental results evidently inspired him to follow up Niels Bohr's idea that the processes powering stars violated energy conservation. Two years later, friendship with George Gamow seems to have led him to sign on to a note about the relation between stellar central temperatures and surface elemental abundances. And in 1937 worries about the intensi.cation of So-viet purges apparently motivated him to return to the stellar-energy problem. Here, as in 1931, Landau developed the view that stars have centrally condensed cores, this time proposing that such cores consist entirely of neutrons. While Landau's idea enjoyed a positive reception from Izvestiia and the Soviet Academy, this response was not suf.cient to keep him out of Soviet jails. The idea did, however, play a major role in initiating Robert Oppenheimer's research into relativistic gravitational collapse, research that would soon lead Oppenheimer to the idea of what would come to be called black holes.
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