Small Black Hole Discovered Outside Galaxy Using New Method

On Nov 13, 2021

A new detection method has been used to discover a small black hole outside the Milky Way, which could pave the way for the discovery of more hidden small black holes within our galaxy as well.

Very large black holes are relatively easy to detect because they give off X-rays as the matter is heated to glowing hot as it is pulled toward the black hole’s event horizon. By looking for these X-rays, or for the gravitational waves given off by black hole collisions, astronomers can spot big black holes. But it’s more difficult to spot smaller black holes which are comparable in mass to our sun because most of them don’t give off either X-rays or gravitational waves.

Artist’s impression showing a compact black hole 11 times as massive as the Sun and the five-solar-mass star orbiting it. — This artist’s impression shows a compact black hole 11 times as massive as the Sun and the five-solar-mass star orbiting it. The two objects are located in NGC 1850, a cluster of thousands of stars roughly 160 000 light-years away in the Large Magellanic Cloud, a Milky Way neighbor. The distortion of the star’s shape is due to the strong gravitational force exerted by the black hole. ESO/M. Kornmesser

But recently, a team using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) was able to spot a black hole that is 11 times the mass of our sun and is located 160,000 light-years away by looking at its gravitational influence on the motion of a nearby star.

“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,” explained lead researcher Sara Saracino from the Astrophysics Research Institute of Liverpool John Moores University in a statement. “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.”

The small black hole is located in a cluster of stars called NGC 1850, which is located in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. This cluster of stars is very young by astronomical standards, at just 100 million years old, and this is the first time a black hole has been observed in such a young cluster. By comparing this small, baby black hole with its older, bigger brethren, astronomers can learn more about how black holes grow and evolve.

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