Black Hole at Milky Ways centre could have devoured its baby brother 120 mln years ago

Astronomers at the Smithsonian Astronomical Observatory in Cambridge, Massachusetts, US have said that the colossal black hole at the centre of the Milky Way galaxy devoured a similar black hole some 120 million years ago.

London, Sept 11 : Astronomers at the Smithsonian Astronomical Observatory in Cambridge, Massachusetts, US have said that the colossal black hole at the centre of the Milky Way galaxy devoured a similar black hole some 120 million years ago.

Scientists say the hypothesis comes from observations of 10 'hypervelocity' stars that are moving so fast that they will eventually escape the galaxy altogether.

Since the first such star was discovered in December 2004, astronomers have suspected that the supermassive black hole at the heart of the Milky Way, which weighs 3.6 million times the Sun's mass, is responsible for catapulting the objects outwards at extreme speeds.

In that scenario, a pair of stars wanders too close to a single, supermassive black hole, and one star gets captured while the other gets flung outwards at up to 4000 km/sec.

But scientists have also proposed alternative models, including a scenario in which a second, middleweight black hole lurks near the larger one and together, both black holes fling stars outwards.

Warren Brown from Smithsonian said, while it is too soon to say which scenario is correct, observations have revealed an intriguing possibility: that a middleweight black hole did exist near the galactic centre at one time, but was swallowed up by its larger neighbour about 120 million years ago.

Brown said they arrived at this possibility after studying the stars' distances and speeds and then calculating when they must have been ejected from the galactic centre.

He said observations revealed that five of the stars seemed to have been evicted around the same time - about 120 million years ago.

"It's possible they came from a single burst. As the smaller black hole fell towards the larger one, the black holes would have gravitationally kicked out a bunch of stars, and we happen to see five of them," Brown said.

He, however, said the small number of observations meant this scenario was only a possibility, and that the stars might have instead have been kicked out one at a time, in unrelated incidents.

Brown said, according to the new study, there could be about 100 hypervelocity stars lying within 330,000 light years of Earth, and that as many as 50 should be observable within the next five years by future sky surveys.

"Those observations may settle the vexing issue of what is slinging the stars out of the galaxy: Is it a single massive black hole ejecting pairs of stars, is it a binary black hole, or is it something else? I think that's probably the biggest question," Brown said.

The study appears in the Astrophysical Journal, reports New Scientist.

ANI