Astronomers have discovered a small black hole in a cluster of stars outside the Milky Way.
They found it by using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) to look at how it influences the motion of a star nearby.
This is the first time this detection method has been used to reveal the presence of a black hole outside of our galaxy.
Researchers suggest the method could be key to unveiling hidden black holes in the Milky Way and nearby galaxies, and to help shed light on how these mysterious objects form and evolve.
The newly discovered black hole was spotted in NGC 1850, a cluster of thousands of stars roughly 160,000 light years away in the Large Magellanic Cloud, a neighbour galaxy of the Milky Way.
Sara Saracino, from the Astrophysics Research Institute of Liverpool John Moores University, said: “Similar to Sherlock Holmes tracking down a criminal gang from their missteps, we are looking at every single star in this cluster with a magnifying glass in one hand trying to find some evidence for the presence of black holes but without seeing them directly.
“The result shown here represents just one of the wanted criminals, but when you have found one, you are well on your way to discovering many others, in different clusters.”
According to the study published in the Monthly Notices of the Royal Astronomical Society, this first “criminal” tracked down by the team is around 11 times as massive as our sun.
Small, stellar-mass black holes have previously been spotted in other galaxies by the X-ray glow emitted as they swallow matter, or from the gravitational waves generated as black holes collide with one another or with neutron stars.
However, most stellar-mass black holes do not give away their presence through X-rays or gravitational waves.
Stefan Dreizler, a team member based at the University of Gottingen in Germany, said: “The vast majority can only be unveiled dynamically.
“When they form a system with a star, they will affect its motion in a subtle but detectable way, so we can find them with sophisticated instruments.”
The method used by Dr Saracino and her team could allow astronomers to find many more black holes and help unlock their mysteries.
Researchers say the detection in NGC 1850 marks the first time a black hole has been found in a young cluster of stars — the cluster is only around 100 million years old.
Even more young black holes could be unveiled using the method, and new light be shed on how they evolve.
By comparing them with larger, more mature black holes in older clusters, astronomers would be able to understand how these objects grow by feeding on stars or merging with other black holes.
The team used data collected over two years with the Multi Unit Spectroscopic Explorer mounted at ESO’s VLT, located in the Chilean Atacama Desert.–PA