Among black hole hunters, a group has dedicated itself to looking for specific types: singularities of intermediate size between the supermassives that roar within the galaxies (such as Sagittarius A *, in the center of the Milky Way) and those born from the collapse of massive stars (sometimes with the mass of the Sun). It was in search of this missing link that two astronomers from the Paris Institute of Astrophysics (IAP) discovered a group of small black holes in the center of a galaxy as old as the Universe.
“Ours is the first study to provide the mass and extent of what appears to be a collection of black holes in the center of a collapsed globular cluster,” said astronomer Eduardo Vitral.
Using the Hubble space telescope, he and his IAP colleague, also astronomer Gary Mamon, searched inside the globular cluster NGC 6397, 7,800 light-years from Earth, for the hypothetical intermediate-sized black hole. This galaxy has one of the densest nuclei known, and when examining it, the researchers came up with a result that did not correspond to what they imagined to find.
“We found very strong evidence of an invisible mass in the dense core of the globular cluster, but we were surprised to find that this extra mass is not punctual, that is, it is not in a single place in space (which would be expected for a massive black hole solitary), but spread over an area within the cluster, “said Stained Glass in a statement.
Astronomers have detected this “invisible mass” using the speeds at which stars travel within the cluster, thus determining the distribution of their total mass (including that of visible stars, those that are not so much and the so-called dark stars): the more mass there is in a region, the faster the stars will transit through it.
“Our analysis indicated that the orbits of the stars are almost random throughout the globular cluster, rather than maintaining systematic circular or elongated movements,” explained Mamon. What would make the stars behave in an astronomically bizarre manner would be remnants of massive stars (white dwarfs, neutron stars and black holes).