An image released by the European Space Agency (ESA) on July 10 shows the likely location of an intermediate-mass black hole in the Omega Centauri star cluster. — AFP
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PARIS: Astronomers announced on Wednesday the strongest evidence yet of a medium-sized black hole, whose absence has long been a cosmic mystery.
The universe is teeming with black holes, from supermassive ones at galaxy centers to smaller ones around 100 times the mass of the Sun. However, finding black holes between these extremes has been challenging, leaving a gap in our understanding of their evolution.
An international team of researchers analyzed Omega Centauri, the largest star cluster in the Milky Way, located about 18,000 light-years from Earth. They discovered “something peculiar,” said Maximilian Haeberle, a PhD student at Germany’s Max Planck Institute for Astronomy.
At the core of this dense cluster of 10 million stars, seven were moving at unusually high speeds. Such velocities should have propelled them out of the cluster, but the gravitational pull of an unseen massive object seemed to be reining them in.
Simulations of the stars’ movements led researchers to conclude there is a black hole at Omega Centauri’s center with a mass of around 8,200 Suns, fitting into the elusive intermediate-mass range.
Supermassive black holes, found at galaxy centers, have more than 100,000 solar masses. For example, the Milky Way’s Sagittarius A* has a mass four million times that of the Sun. Smaller stellar-mass black holes, formed from supernova explosions of giant stars, range from five to 150 solar masses.
Between these two categories lies a significant gap, home to the so-called intermediate-mass black holes (IMBH), said Haeberle, lead author of a new study published in Nature.
Although scientists believe IMBHs exist, they have identified very few candidates. Black holes are inherently difficult to observe as they trap even light. One detection method involves observing the massive energy released when they consume gas and dust. However, IMBHs consume less gas, making them even harder to detect, Haeberle explained.
Spotting one “is like finding the first evidence for Bigfoot — people are going to freak out,” said study co-author Matthew Whittaker of the University of Utah in a statement.
Haeberle hopes this discovery will end nearly two decades of debate among astronomers about whether Omega Centauri hosts an IMBH.
The researchers analyzed 20 years of publicly available data from the Hubble Space Telescope, tracking the movements of 1.4 million stars in Omega Centauri. They ruled out other potential causes for the seven stars’ high speeds, such as multiple stellar-mass black holes or binary star systems, Haeberle said.