Black holes eat like pigs. Put food in front of them -- any form of matter will do -- and they stuff their faces so voraciously that the friction generated around their cosmic lips triggers a tremendous outpouring of energy, everything from radio waves to high-powered X-rays.

But black holes sometimes take inexplicable breaks. The one at the center of our galaxy, for example, seems to be dieting right now. Barely nibbling at its surroundings, it emits only radio signals.

As recently as a few centuries ago, according to a new study of X-ray energy, our Milky Way's black hole went on a feeding frenzy fueled by an exploding giant star. This supernova, as it is called, sent a shock wave of heavy metals plowing into the gravity sink. Once the material was gobbled up, researchers suspect, the black hole reverted to starvation.

"I would dare to say the hypothesis is probably 75-percent likely," said Penn State University's Yoshitomo Maeda, who led the study.

Maeda told SPACE.com that if supernovae can in fact serve as on/off switches in this manner, they might control the appetites of black holes throughout the universe. Another recent study found that 90 percent of black holes are inactive at any given time, but evidence indicates that something reactivates them, because they continue to grow.

Maeda notes, however, that other unknown on/off switches could be at work.