In earlier times, it was believed that black holes come in only two “sizes”. There are black holes with a mass of 5 to 30 times the mass of the Sun, and at the other end of the scale, there were supermassive black holes located in the central regions of galaxies and has a mass of several million solar masses. As astronomical technologies improved and new tools appeared, scientists began to receive confirmation of the existence of intermediate-class black holes with a mass of 10 to 10 thousand solar, at the same time the first of ultra-supermassive black holes with masses exceeding the mass of the Sun more than a billion times were found.
Given all of the above, it can be assumed that there must also be a class of ultra-small black holes with a mass of 2.1 to 5 solar masses because the number 2.1 is a kind of boundary. If the mass of the exploding star is less, then a neutron star is formed as a result of the supernova explosion, if it is more, then a black hole. And recently, astronomers from Ohio University discovered a black hole, the smallest known to date, which is the first representative of a new class of these space objects.
Small black hole detection was the result of “sifting data” collected by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) tool, which measures the emission spectra of stars. Scientists were looking for deviations in the spectrum that would indicate that the stars revolve around a conditionally invisible object. And from the entire array of 100 thousand stars, 200 were chosen, which seemed to the scientists the most interesting. After that, as part of the All-Sky Automated Survey for Supernovae survey, thousands of images of each star were made.
As a result of the analysis of all the new data collected, scientists had only one potential candidate – the giant red star 2MASS J05215658 + 4359220, which revolves around something invisible to modern astronomical instruments. But the calculations showed that with a very high percentage of probability this invisible object is a black hole, the mass of which is 3.3 times the mass of the Sun.
“What we did in our work is a completely new method of searching for black holes. And this method allowed us to immediately find the first representative of the class of small black holes, the existence of which astronomers could only have guessed earlier,” scientists write, “We collected the data have already told us a lot about the processes of formation, evolution and the “character” of these new space objects for astronomy”.