Kip Thorne recalled that physicists were initially skeptical of the model, viewing as "truly strange" at the time. He explained further, "It was hard for people of that era to understand the paper because the things that were being smoked out of the mathematics were so different from any mental picture of how things should behave in the universe." Oppenheimer himself thought little of this discovery. However, some considered the model's discovery to be more significant than Oppenheimer did, and model would later be described as forward thinking. Freeman Dyson thought it was Oppenheimer's greatest contribution to science. Lev Davidovich Landau added the Oppenheimer-Snyder paper to his "golden list" of classic papers. John Archibald Wheeler was initially an opponent of the model until the late 1950s, when he was asked to teach a course on general relativity at Princeton University. Wheeler claimed at a conference in 1958 that the Oppenheimer-Snyder model had neglected the many features of a realistic star. However, he later changed his mind completely after being informed by Edward Teller that a computer simulation ran by Stirling Colgate and his team at the Lawrence Livermore National Laboratory had shown a sufficiently heavy star would undergo continued gravitational contraction in a manner similar to the idealized scenario described by Oppenheimer and Snyder. Wheeler subsequently played a key role in reviving interest in general relativity in the United States, and popularized the term "black hole" in the late 1960s. By the late 1960s and early 1970s, advances in observational astronomy, such as radio telescopes, changed the attitude of the scientific community. Pulsars had already been discovered and black holes were no longer considered mere textbook curiosities. Cygnus X-1, the first solid black-hole candidate, was discovered by the Uhuru X-ray space telescope in 1971. Jeremy Bernstein described it as "one of the great papers in twentieth-century physics."