For nearly a decade, scientists have been hunting for the gravitational wave background, a faint but persistent echo of gravitational waves thought to have been set off by events that took place ...

But an expected corresponding low-frequency gravitational wave background—a kind of "hum" comprised of a chorus of gravitational waves, most likely emanating from binary pairs of supermassive ...

Still, even if it is supermassive black holes causing the hum, such a finding will tell scientists more about how supermassive black holes grow and evolve.