It seems the answer may simply be that we didn't catch the cosmic monster—weighing at least four million times the mass of our sun—feeding at the right time, according to a new study.

"If we had been around to see it two million years ago, the situation would have been very different," said study co-author Philip Maloney of the University of Colorado in Boulder.

"The Milky Way's black hole was maybe ten million times brighter [then]," he said. "I don't think anyone really had any expectation that SMBH might vary in luminosity by such a huge factor on such a short—relatively speaking—time scale."

(See "Monster Black Holes Gobble Binary Stars to Grow?")

Astronomers have long suspected there was an ancient outburst from