A very small black hole, at least compared to the supermassive black holes that are normally discussed, was discovered by a research team that analyzed a catalog of 100,000 stars called the Apache Point Observatory Galactic Evolution Experiment (APOGEE). The black hole is characterized by a mass that seems to be only 3.3 times the mass of the Sun. The study was published in Science magazine.
About 10,000 light-years away, this black hole is located in the outer area of the main Milky Way disc and, if the size was confirmed, it would be the smallest black hole ever found, so small that it would enter a new class. The diameter of the black hole should actually be only 19 km, but further observations would be required to confirm this data.
Researchers usually detect black holes by intercepting a growth disk consisting mainly of gas and dust, the turbines of which surround the object. If there is no gas and dust disk that turbulates, heats, and emits X-rays, it is impossible to identify the black hole unless it is part of an interacting binary system, i.e. a system consisting of a black hole and another object, such as a star, in which the former sucks in material from the latter.
In this case, however, there was no disc with gas and dust, and although the black hole was part of the binary system, it did not appear to interact. However, the researchers were still able to find the black hole due to the fact that this black hole is in the binary system.
Analyzing the data in the above catalog, the researchers focused on a specific binary star system called J05215658, and realized that one of the two stars is actually a black hole, which rotates around a giant star every 83 days. In this case, the researchers noticed the presence of a black hole analyzing the light of the star, a giant star whose light seems to be “shifted”. The brightness of a star essentially continues to change, increase and decrease, a sign that there is something in orbit around it.
These variations indicate the presence of a double companion, which, since it does not emit light, must be a black hole. The latter does not seem to have swallowed any material and has been identified only by this particular distorting characteristic of the star’s light.
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