解析库 > 2021年10月全球GRE机经题
The suggestion that quasars emit so much energy because they are powered by black holes was made in the 1960s, soon after quasars were first discovered. But black holes were still a novel concept, and because staggeringly massive black holes were required to explain quasar luminosity, most astronomers focused on other sources of power for quasars, such as neutron stars or collapsing gas clouds. Over the next two decades, however, these models were found incapable of explaining the growing body of observations of quasars. Furthermore, other studies showed that the objects posited by these models would eventually evolve into black holes containing most of the mass of the original system, thereby suggesting that the formation of massive black holes is natural and perhaps even inevitable.