Black holes don’t emit light, so finding them is far from easy. They are either caught while eating – siphoning material so quickly that said material starts glowing – or if they collide and release enough gravitational waves that we can detect them.
Spotting the quieter, smaller black holes is much more difficult. Astronomers can try to look for peculiar motions in nearby stars. By doing so, a team discovered a new small black hole in the Large Magellanic Cloud, the largest companion galaxy to our own.
As reported in the Monthly Notices of the Royal Astronomical Society, the black hole is 11 times as massive as the Sun – relatively small for the class of stellar-mass black holes, and tiny compared to the supermassive black holes at the center of the galaxy which weigh millions if not billions of times that of our Sun.
The black hole is located in a stellar cluster called NGC 1850. While not the first black hole discovered in a stellar cluster, this is the first discovered in a young cluster. This group of stars is only 100 million years old, an infant in cosmic terms. Finding such an object is really exciting, made possible by looking at the motion of its companion star, which weighs about five times our Sun.
“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,” lead author Sara Saracino from the Astrophysics Research Institute of Liverpool John Moores University, said 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.”
Sophisticated instruments and an unconventional technique were required to reveal a black hole like this. The team employed the Multi-Unit Spectroscopic Explorer (MUSE) mounted at ESO’s Very Large Telescope, collecting observations over two years. The instrument allows researchers to study individual members of crowded regions such as star clusters, capturing data about 1,000 stars in one shot.
Future observations hope to look at even younger clusters to understand them and their black holes in their formative years, as well as compare them with older clusters and black holes already known and yet to be discovered.
“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.
When the Extremely Large Telescope comes online later this decade, even more of these hidden black holes may be found.
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