Black Hole Ripped From Relic Galaxy

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A middle-weight black hole — the first object of its size found — is shrouded by a cluster of young stars, evidence that the black hole may have once prowled in another galaxy, scientists reported Monday.

Discovered in 2009, the black hole, which is about 20,000 times more massive than the sun, lies toward the edge of the galaxy ESO 243-49, located about 290 million light years from Earth. It was the first intermediate-sized black hole found.

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Follow-up research published this week shows the black hole, known HLX-1, is shrouded in a cluster of stars estimated to be less than 200 million years old — too young for their present surroundings.

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Scientists believe the star cluster formed as result of a crash between a dwarf galaxy and the larger ESO 243-49. The collision would have not only stripped stars away from the the dwarf galaxy, but also triggered a new wave of star formation. That means that HLX-1 may have once been the core of that now-disintegrated relic dwarf galaxy.

The research has implications for understanding how galaxies and super-massive black holes, such as the 4-million solar mass monster at the center of the Milky Way, form.

“For the first time, we have evidence on the environment, and thus the origin, of this middle-weight black hole,” Mathieu Servillat, previously with the Harvard-Smithsonian Center for Astrophysics, said in a statement.

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While giant stars’ collapses can form black holes up to about 10 times the mass of the sun, scientists aren’t sure how super-massive black holes form. One theory is that they build up over time by merging with smaller, intermediate-sized black holes — objects like HLX-1.

“This black hole is unique in that it’s the only intermediate-mass black hole we’ve found so far. Its rarity suggests that these black holes are only visible for a short time,” Servillat said.

The research appears in this week’s Astrophysical Journal

Image: The black hole at the edge of galaxy ESO 243-49 may have been salvaged from another galaxy. Credit: NASA/ESA/S.Farrell at University of Sydney and University of Leicester

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