Ashutosh Jogalekar in The Curious Wavefunction:
On September 1, 1939, the same day that Germany attacked Poland and started World War 2, a remarkable paper appeared in the pages of the journal Physical Review. In it J. Robert Oppenheimer and his student Hartland Snyder laid out the essential characteristics of what we today call the black hole. Building on work done by Subrahmanyan Chandrasekhar, Fritz Zwicky and Lev Landau, Oppenheimer and Snyder described how an infalling observer on the surface of an object whose mass exceeded a critical mass would appear to be in a state of perpetual free fall to an outsider. The paper was the culmination of two years of work and followed two other articles in the same journal.
Then Oppenheimer forgot all about it and never said anything about black holes for the rest of his life.
He had not worked on black holes before 1938, and he would not do so ever again. Ironically, it is this brief contribution to physics that is now widely considered to be Oppenheimer’s greatest, enough to have possibly warranted him a Nobel Prize had he lived long enough to see experimental evidence for black holes show up with the advent of radio astronomy.
What happened?
More here.