In 1939, Einstein published a paper that argued against the existence of Black holes. Einstein used his own general theory of relativity to arrive at this conclusion. A few months after Einstein rejected the existence of Black holes, Oppenheimer and his student Hartland Snyder published a paper that revealed, for the first time, using Einstein's general theory of relativity, how Black holes would form. Though Oppenheimer and Einstein later met, there's no record of them having discussed Black holes.