Black Hole Woke for Feeding in 18th Century

April 17, 2008 -- About 300 years ago, the black hole lurking in the heart of the Milky Way galaxy woke from hibernation and entered a feeding frenzy, triggering a cascade of X-rays that reverberated off nearby clouds. The energy released by the event was so intense, echoes remain etched in an interstellar cloud today.

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

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

The scientists combined data from a trio of probes scouting the cosmos for X-rays. 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.

Using a technique pioneered only a year earlier, the researchers showed the echoing light waves emanated from the black hole, rather than being triggered by subatomic particles, for example.

The key to unraveling the X-ray source was the detection of iron molecules in the spectral data, which shows the chemistry of areas the light had passed through.

Scientists believe the black hole's frenzy spewed out X-rays that blasted electrons off iron molecules in the cloud. The shift of electrons to and fro triggered sensors in X-ray detectors on U.S., European and Japanese satellites.