Very Large Telescope discovers black hole hiding in a star cluster outside Milky Way

Astronomers have used the European Southern Observatory’s Very Large Telescope (ESO’s VLT) to discover a new black hole they claim is hiding within a star cluster outside the Milky Way.

According to the astronomers, the new black hole is lurking in NGC 1850, a cluster of thousands of stars roughly 160 000 light-years away in the Large Magellanic Cloud. The black hole is influencing the movement of a star in its close vicinity.

The new black hole is roughly 11 times as massive as our Sun and its gravitational influence on the five-solar-mass star orbiting it gave away its existence.

Astronomers have previously spotted such small, “stellar-mass” black holes in other galaxies by picking up 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.To carry out their search, the team used data collected over two years with the Multi Unit Spectroscopic Explorer (MUSE) mounted at ESO’s VLT, located in the Chilean Atacama Desert.

However, most stellar-mass black holes don’t give away their presence through X-rays or gravitational waves. “The vast majority can only be unveiled dynamically,” says Stefan Dreizler, a team member based at the University of Göttingen in Germany. “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.

This dynamical method used by Saracino and her team could allow astronomers to find many more black holes and help unlock their mysteries. “Every single detection we make will be important for our future understanding of stellar clusters and the black holes in them,” says study co-author Mark Gieles from the University of Barcelona, Spain.

The NGC 1850 is a young cluster of star – around 100 million years old – and it is for the first time that a black hole has been discovered in such a young star cluster. Using the methods employed in this discovery, astronomers are optimistic that they could unveil even more young black holes and shed new light 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. Furthermore, charting the demographics of black holes in star clusters improves our understanding of the origin of gravitational wave sources.

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