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‘Middleweight’ black hole discovered in world first

The 'middleweight' black hole weighs 2,200 times the mass of the Sun.

The 'middleweight' black hole weighs 2,200 times the mass of the Sun. Photo: Supplied: Bülent Kiziltan and Elif Mokran/ABC

A Queensland scientist has played a vital role in the world-first discovery of a “middleweight” black hole in space, spending 40 years searching the universe to find it.

University of Queensland astronomer Associate Professor Holger Baumgardt said it was the missing link between small and super-sized black holes.

Dr Baumgardt said the discovery would help astronomers understand galaxies and how galaxies have formed and evolved.

He said black holes were normally either small and weighed a few times the Sun’s mass, or supermassive, and weigh millions of times the Sun’s mass.

But this study showed the first proof of an intermediate-mass black hole existing – weighing 2200 times the mass of the Sun.

Queensland scientists performed computer simulations

The researchers, led by Dr Bulent Kiziltan of the Harvard-Smithsonian Centre for Astrophysics in the United States, relied on computer simulations by the Queensland scientists to look for clues in space.

“An intermediate-mass black hole at the cluster’s centre acts like a cosmic ‘spoon’ that stirs the pot, causing the stars near it to slingshot to higher speeds and greater distances, imparting a subtle signal that astronomers can measure.”
Associate Professor Holger Baumgardt

By employing simulations of stellar motions and distances, and comparing them with visible-light observations, the team found evidence for just this sort of gravitational stirring.

He said the second line of evidence came from pulsars, compact remnants of dead stars with radio signals that were easily detectable.

“These objects were also flung about due to the gravitational influence of the central intermediate-mass black hole, causing them to be found at greater distances from the cluster’s centre than would be expected if no black hole existed,” Dr Baumgardt said.

Black hole hid in 12-billion-year-old star cluster

The discovery was announced on Thursday in the journal Nature, revealing the black hole hid at the centre of the 12-billion-year-old globular 47 Tucanae star cluster.

It is 13,000 light years from Earth in the southern constellation of Tucana the Toucan.

It contains 3 million stars and holds about two dozen pulsars that are important targets of this investigation.

In their paper, the researchers said 47 Tucanae had been examined previously for a central black hole, without success.

Dr Kiziltan said in most cases, a black hole was found by looking for X-rays emanating from a hot disk of material swirling around the black hole.

47 Tucanae

The black hole hid at the centre of the 47 Tucanae star cluster. Photo: Supplied: NASA/ESA

This method only worked if the black hole was actively feeding on nearby gas.

“The centre of 47 Tucanae is gas-free, effectively starving any black hole that might lurk there,” Dr Kiziltan said.

“A supermassive black hole at the centre of the Milky Way gives clues to its presence by its influence on nearby stars.

“Years of infrared observations have shown a handful of stars at our galactic centre whipping around an invisible object with a strong gravitational tug.

“But the crowded centre of 47 Tucanae makes it impossible to watch the motions of individual stars.”

This was why the hunt for the “missing link” across the cosmos was so challenging, he said.

Life in the universe remains a mystery

However, the discovery would not help find out more about life in space, Dr Baumgardt said.

“What we have found is not telling us anything about life in the universe, because a black hole is a place where there should be no life, but it tells us something about the evolution of galaxies on a large scale.”

“Anything which comes too close to the black hole will basically fall into the black hole and have no chance of ever getting out again.”

The researchers said their discovery would help them unlock the link between the smaller mass black holes and super ones that could be found in the centre of galaxies.

“Of course we got very excited because we’ve been looking for black holes for a very long time,” Dr Baumgardt said.

“We are already working on a second cluster to find a second ‘middleweight’ black hole.”

Researchers said the fact this black hole had eluded detection for so long suggested black holes of similar masses could be hiding in other globular clusters.

-ABC

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