The binary system formed by a blue star, LB-1, visible on the left, and by a 70 solar masses black hole, in the center of the image (artist impression). The black hole is surrounded by an accretion disk formed by gas torn from the star. The inner edge of the disk is truncated, so it does not reach the black hole. This is the probable reason why X-ray emissions from this binary system were not observed, despite the accurate research carried out with the Chandra space telescope [Jingchuan YU, Beijing Planetarium, 2019]

An Oversized Stellar-Mass Black Hole

A study published on November 27 in Nature received extensive media coverage. It describes the discovery of an unusual stellar black hole with a mass of almost 70 suns. The existence of such a massive black hole contradicts current models of stellar evolution, which could be wrong. However, there are alternative explanations, which can account for what has been observed without necessarily contradicting the theory

Stars with initial masses of at least 20–25 solar masses end their existence as black holes: once the fuel that feeds the nuclear fusion is exhausted, their cores collapse under the overwhelming pressure of their gravity, forming stellar-mass black holes. If the progenitor star was not part of a binary system, discovering the black hole produced by it is almost impossible. Black holes do not emit radiation, so there is no way to identify their presence if they are in isolation [1].

The case of binary systems formed by a black hole and a star in close orbit is different: in this case, the extreme gravity exerted by the black hole tears matter from the companion star; this…