Black hole found hiding in a star cluster outside our galaxy

Black hole found hiding in a star cluster outside our galaxy

This artist’s impression shows a compact black hole that is 11 times as massive as the Sun and the five-star mass orbiting it. The two objects are located in NGC 1850, a cluster of thousands of stars about 160,000 light-years away in the Great Magellanic Cloud, a Milky Way neighbor. The distortion of the shape of the star is due to the strong gravity exerted by the black hole. The gravitational force of the black hole not only distorts the shape of the star, but it also affects its orbit. By looking at these subtle orbital effects, a team of astronomers was able to deduce the presence of the black hole, making it the first small black hole outside our galaxy to be found this way. For this discovery, the team used the instrument Multi Unit Spectroscopic Explorer (MUSE) at ESO’s Very Large Telescope in Chile. Credit: ESO / M. Grain knives

Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), astronomers have discovered a small black hole outside the Milky Way by looking at how it affects the motion of a star in its vicinity. This is the first time this detection method has been used to detect the presence of a black hole outside our galaxy. The method may be the key to revealing 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 seen lurking in NGC 1850, a cluster of thousands of stars about 160,000 light-years away in the Great Magellanic Cloud, a neighboring galaxy to the Milky Way.

“Like Sherlock Holmes tracing a criminal gang from their missteps, we look at every single star in this cluster with a magnifying glass in one hand and try to find evidence of the presence of black holes, but without seeing them. directly, “said Sara Saracino of the Astrophysics Research Institute at Liverpool John Moores University in the UK, who led the research, which has now been accepted for publication in Monthly announcements from the Royal Astronomical Society. “The result shown here represents just one of the wanted criminals, but once you find one, you’re well on your way to discovering many others, in different clusters.”

This first “criminal”, who was tracked down by the team, turned out to be about 11 times as massive as our sun. The smoking gun that put astronomers on the trail of this black hole was its gravitational pull on the five-solar mass star orbiting it.

Astronomers have previously seen such small black holes with “star mass” in other galaxies by capturing the X-ray emitted when they swallow matter, or from the gravitational waves generated when black holes collide with each other or with neutron stars.

However, most black holes with star mass do not give their presence away through X-rays or gravitational waves. “The vast majority can only be revealed 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 dynamic 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 star clusters and the black holes in them,” said study co-author Mark Gieles of the University of Barcelona, ​​Spain.

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 about 100 million years old, a blink of an eye on astronomical scales). Using their dynamic method in similar star clusters could reveal even more young black holes and shed new light on how they evolve. By comparing them to larger, more mature black holes in older clusters, astronomers would be able to understand how these objects grow by eating off stars or merging with other black holes. Furthermore, mapping the demographics of black holes in star clusters improves our understanding of the origin of gravitational wave sources.

To conduct their search, the team used data collected over two years with the Multi Unit Spectroscopic Explorer (MUSE) mounted on ESO’s VLT located in the Chilean Atacama Desert. “MUSE allowed us to observe very crowded areas, such as the innermost areas of star clusters, and analyze the light from every single star nearby. The net result is information about thousands of stars in one shot, at least 10 times more than with any other instrument, “says co-author Sebastian Kamann, a longtime MUSE expert based at Liverpool’s Astrophysics Research Institute. This allowed the team to spot the strange star whose peculiar motion signaled the presence of the black hole. Data from the University of Warsaw’s Optical Gravitational Lensing Experiment and from the NASA / ESA Hubble Space Telescope enabled them to measure the mass of the black hole and confirm their results.

ESO’s Extremely Large Telescope in Chile, which is due to start operating later this decade, will allow astronomers to find even more hidden black holes. “ELT will definitely revolutionize this field,” Saracino says. “It will allow us to observe stars significantly fainter in the same field of view, as well as to look for black holes in globular clusters that are located at much greater distances.”

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More information:
S Saracino et al., A black hole discovered in the young massive LMC cluster NGC 1850, Monthly announcements from the Royal Astronomical Society (2021). DOI: 10.1093 / mnras / stab3159

Citation: Black hole found hidden in star cluster outside our galaxy (2021, November 11) retrieved November 11, 2021 from

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