About 300 years ago, the black hole lurking in the heart of the Milky Way woke from hibernation and entered a feeding frenzy, triggering a cascade of x-rays that reverberated off nearby clouds, researchers say.

The energy released by the event was so intense that echoes remain etched in an interstellar cloud today.

The findings, reported by Japanese astronomers, may explain why our galaxy's black hole, known as Sagittarius A*, is so laid-back compared to similarly sized monsters in other galaxies.

"Perhaps it's just resting after a major outburst," says Kyoto University's Tatsuya Inui, lead author of a paper in the Publications of the Astronomical Society of Japan.

Data taken between 1994 and 2005 revealed a quick-lived but intense flash of x-rays from a large cloud known as Sagittarius B2, which lies 300 light-years from the Milky Way's black hole.

Scientists believe the black hole's frenzy spewed out x-rays that blasted electrons off iron molecules in the cloud.