According to a team of astrophysicists, the most massive globular cluster in the neighboring galaxy Andromeda could harbor an intermediate-mass black hole. However, no object of this type has yet been detected with certainty.
There are three types of black holes in the Universe. The first, those of stellar mass, are formed by the collapse of a massive star and have a mass between ten and a hundred times that of the Sun. Supermassives have masses equivalent to millions or billions of suns. The latter are most often posted at the center of the galaxies. And between these two extremes are more withdrawn members of the black hole family:those of intermediate mass, whose mass range varies from 100,000 to a million solar masses.
We know that these "missing links" exist in theory. On the other hand, they are particularly difficult to find. Suspects have already been identified, but none of them have yet been truly confirmed. This new study, reported in The Astrophysical Journal, presents a new candidate.
The suspect is in the globular cluster B023-G078 , located on the outskirts of the Andromeda Galaxy, about 2.5 million light-years away of the earth. Researchers believe the cluster, which contains the mass of 6.2 million suns , is actually just a stripped core. According to them, it would be the remains of several small galaxies that once merged. At the center of this galactic hodgepodge would then be an intermediate-mass black hole.
As part of this work, the team of scientists relied on new observations from the Gemini Observatory and the Hubble Space Telescope to calculate the mass distribution in the cluster. By then modeling the velocities of the stars moving inside, the researchers determined that without a black hole in the center, these stars should move less rapidly .
"The stellar speeds we are getting give us direct evidence that there is some sort of black mass right in the center “Summarizes Renuka Pechetti, an astrophysicist at Liverpool John Moores University. “It is very difficult for globular clusters to form large black holes. However, if it's in a stripped core, then there must already be a black hole present, left as a remnant of the smaller galaxy that fell into the larger one “.
Great uncertainty remains, however. According to the team, what appears to be a single black hole may actually be a multitude of stellar-mass black holes close enough together to be seen as a single object.
Future observations, especially in the infrared thanks to the James Webb Telescope, could help astrophysicists determine its true nature. The researchers also plan to examine three other globular clusters within the same galaxy.
