Hubble sees double Grad student Hsiang-Chih Hwang helps refine the technique for identifying quasar pairs, 'opening the floodgates' for the discovery of merging galaxies and revealing more information about galaxy formation and gravitational waves By Rachel Wallach / Published April 28, 2021 Astrophysicists know that just about every large galaxy has a supermassive black hole at its center. They know that when galaxies merge, so, ultimately, do their black holes. But they don't yet know much about how the merging process occurs, or exactly what happens to the supermassive black holes during it. That's because there haven't been many examples to study. Scientists search for supermassive black holes by looking for quasars, the brilliant objects formed when supermassive black holes feed on bits of matter, which emits copious radiation as it falls into the black hole. Most galaxy mergers happened 10 billion years ago, and when looking that far into the past, quasars are scattered widely across the universe. For every thousand quasars, it's estimated there is just one double one. Most quasar pairs known to date are still far apart, and not yet close to the final merging phase. Scanning the skies randomly with even the highest-powered telescope, it could take millennia to find more than a handful of mergers in process.