Every galaxy has a supermassive black hole at its center, much like every egg has a yolk. But sometimes, hens lay eggs with two yolks. In a similar way, astrophysicists like us who study supermassive black holes expect to find binary systems ' two supermassive black holes orbiting each other ' at the hearts of some galaxies. Black holes are regions of space where gravity is so strong that not even light can escape from their vicinity. They form when the core of a massive star collapses on itself, and they act as cosmic vacuum cleaners. Supermassive black holes have a mass a million times that of our Sun or larger. Scientists like us study them to understand how gravity works and how galaxies form. Figuring out whether a galaxy has one or two black holes in its center isn't as easy as cracking an egg and examining the yolk. But measuring how often these binary supermassive black holes form can help researchers understand what happens to galaxies when they merge. In a new study, our...
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