Then again, the strange body could be a rare type of supernova or an oddball "midsize" black hole—more massive than black holes born when single stars explode but "lighter" than the supermassive ones at the centers of galaxies.

"All three of those [options] are exotic and have something peculiar to them," said study co-author Peter Jonker, an astronomer with the Netherlands Institute for Space Research in Utrecht.

Jonker and his colleagues found the mystery object while on the hunt for off-center supermassive black holes that are thought to form when two galaxies merge. (Related: "Colossal Four-Galaxy Collision Discovered.")

Most, if not all, galaxies