Astronomers Puzzled By Black Hole

The researchers didn't offer a definitive explanation for the phenomenon. But it's clear, they wrote, that there's some sort of gap or instability in the accretion disk, the ring of infalling material surrounding the black hole. Maybe something about the disk itself causes the matter to fall into the black hole in a regular pattern, or maybe something in its vicinity (perhaps another black hole) is disrupting the disk in a cyclic way, they suggested.