It is a rare black hole of intermediate size, is located near the Milky Way and is very special: the discovery of some scientists
Black holes are among the strangest and most fascinating celestial bodies. They represent for us one of the few "unknown" elements, of which scientists still do not know how to give an explanation. From Interstellar to The Simpsons, from The Big Bang Theory to Star Trek: the black hole is part of our film and television culture.
But scientists have recently discovered a very special black hole. Let's try to understand what it is.
What we know about black holes
A black hole is a celestial body with a gravitational field that has a force of attraction so strong that it does not let anything escape: matter, radiation, light.
It is born from the implosion of a star with a very high mass, at least three times that of the sun. At its center is a singularity, a point that defies the laws of general relativity and is still a mystery to scientists.
For these reasons, it is very difficult to directly observe a black hole. In 2019 we got the first image of a black hole, blurry and after two years of intense work. It's the photo of the century.
Scientists have found two types of black holes, based on their size: there are stellar-mass ones, up to 100 times the mass of the Sun, and supermassive ones, which start at about a million times the mass of the Sun.
The discovery of an anomalous black hole
An international team of scientists has recently discovered a black hole of intermediate size: it is the first of this type, and is located in the Andromeda Galaxy, the closest to our Milky Way.
In particular, it would be at the center of a globular cluster called B023-G078, the most massive in the Galaxy, which could be the "fossil" of an old, small galaxy sucked out of Andromeda. The discovery of the black hole was made by studying the metal content of the cluster, based on the light it emits. In this way it was also possible to determine that the black hole has an age of 10.5 billion years. It is not the first time that a black hole is discovered in a star cluster outside the Milky Way.
The mass of the black hole was instead calculated based on the way in which the stars move around the center of the cluster: we now know that the black hole is about 91 thousand times the size of the Sun.