A rare black hole that survived galaxy destruction

Astronomers have spotted a rare mid-weight black hole some 290 million light-years from Earth.

Washington: Astronomers have spotted a rare mid-weight black hole some 290 million light-years from Earth which they say offers clues about a now-destroyed galaxy that may once have existed around it.

Researchers at the Sydney Institute for Astronomy in Australia who spotted the black hole using the Hubble Space Telescope think the dwarf galaxy was torn apart by the gravity of a larger host galaxy that it orbited.

The violent encounter, they believe, would have stripped away most of the dwarf galaxy`s stars, but it also could have compressed the gas around its central black hole, triggering a new wave of star formation, LiveScience reported.

It is these new stars that Hubble recently saw signs of. And the observations suggest that the young stars must be less than 200 million years old, the researchers said.

It means the collision between the parent galaxy and its dwarf likely occurred around that time, they added. "The fact that there`s a very young cluster of stars indicates that the intermediate-mass black hole may have originated as the central black hole in a very low-mass dwarf galaxy. The dwarf galaxy was then swallowed by the more massive galaxy," lead researcher Sean Farrell said.

Besides revealing clues about the lost galaxy, the black hole itself, called HLX-1 (Hyper-Luminous X-ray source 1), is scientifically interesting, the researchers reported in the Astrophysical Journal Letters.

The black hole, which contains the mass of about 20,000 Suns, was spotted, was earlier thought to be representing a class of middle-weight black holes that are the building blocks for the supermassive black holes lurking at the centre of most large galaxies, including our own Milky Way.

"This black hole is unique... Its rarity suggests that these black holes are only visible for a short time," Mathieu Servillat, another researcher who conducted his work at the Harvard-Smithsonian Center for Astrophysics in the US, said.

By studying this rare middleweight black hole, the researchers hope to learn more about how they, and their larger supermassive brethren, form, he said.


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