According to a study published in the journal Science, scientists may have discovered the smallest black hole ever discovered. This has been made possible thanks to a new technique that combines several data sets. Researchers believe that the black hole is about 3.3 times more massive than the Sun and is located in the binary system J05215658, which is located at a distance of about 10,000 light-years from the outer edge of the Milky Way disk. Although more research is needed to confirm the small mass of the black hole, it is likely that this object is part of a mysterious class of small black holes. These objects were not discovered in the past, since no one understood exactly how to look for them.
Can small black holes exist?
Most of the observed black holes are about 5-15 times more massive than the Sun, but this does not mean that all black holes in the Universe are of this size. Part of the fact is that massive and supermassive black holes are much easier to detect. When such objects revolve around stars in binary systems, they attract material from their satellites. This accretion process emits x-rays that can be observed with telescopes.
Small black holes, which are only two to five times more massive than the Sun, provided that they exist, do not seem to produce this x-ray signature, which makes these objects invisible to scientists. When a star becomes a supernova, the subsequent evolution of the star is determined by its mass. Small stars become neutron stars – the densest objects in the universe, while large stars collapse into black holes. However, researchers cannot yet say how massive the star must be in order to become a black hole. It is possible that there is an intermediate process in which a star temporarily becomes a neutron star, and then evolves into a black hole.
Scientists wanted to find out if there is anything in common between the most massive neutron stars known today (whose mass is approximately 2.1 times the mass of the Sun) and the least massive black holes whose mass does not exceed five solar masses.
To fill this gap, a team of researchers screened observations of about 100,000 stars in the Milky Way using an Apog Point Observatory galaxy experiment (APOGEE). Scientists have looked for signs of stars in binary systems with black holes in much the same way as some exoplanet researchers look for worlds around other stars. Observing how stars influence gravity from nearby objects, the team narrowed the search to several hundred candidates who may have satellites. The researchers then used automated supernova survey data (ASAS-SN) to further search for the desired system. As a result, combining the two data sets, scientists found the same star. According to the publication Vice, the new method was incredibly effective in finding previously invisible objects.
Despite the fact that according to the most probable estimates, the mass is equal to 3.3 solar masses, the researchers do not exclude that the object J05215658 could potentially be about five times more massive than the Sun. Earlier, several other black holes were discovered, the mass of which researchers are still arguing about, so at the moment it is impossible to say with certainty that the new object is the smallest of all known black holes today. Nevertheless, the very assumption that the most mysterious objects in the Universe can be even more mysterious should probably not surprise us.