Black holes would not only be born from a massive star, they would also arise from the union of star clusters.
A group of scientists from Chile proposed a new origin for the supermassive black holes that inhabit the center of galaxies, such as the Sagittarius A* (Sgr a*) of the Milky Way. According to a report published in the Monthly Notices of the Royal Astronomical Society magazine, gravitational phenomena would also be formed by the accumulation and merger between nearby stars.
In recent decades, astronomers have determined that a black hole is born when a medium-mass star dies and collapses in on itself. The enormous amount of matter in the celestial body is compressed so much that it causes gravitational forces high enough to prevent light from escaping its zone of influence. As a general rule, the bigger a star, the bigger its supermassive black hole will be.
For the Latin American team, there is a second way in which black holes could arise. Nuclear star clusters, where groups of smaller stars interact, could coalesce and form gravitational instability that ultimately results in one of these space phenomena. Nuclear star clusters are very dense and are made up of very old and massive stars that have clumped together in the center of galaxies due to gravity. In the document they propose a limit of concentrated matter from which the emergence of black holes is triggered.
“The finding implies the existence of a critical mass for nuclear star clusters, which if it is exceeded, there would be an instability produced by the constant collision between stars, which can form a black hole,” explained Andrés Escala, an astronomer from the University of From Chile.
For their report, the scientists created a computer simulation where they observed the evolution of star clusters at the center of galaxies. Thanks to the Kultrun supercomputer at the University of Concepción in Chile, they predicted growth and collisions between stars and more matter. Mathematically speaking, the sum of several stars could also explain the emergence of holes like Sgr A* whose nature is still a mystery.
Sagittarius A* is the most famous hole detected in the Milky Way. It is located 27 thousand light years from Earth right in the central part of the galaxy. We are barely getting to know Sgr a* and for now we only have a kind of photograph showing its growth disk. Evidence was recently found indicating that at times he wakes up and unleashes his fury.
There are black holes closer to our planet. Gaia BH1 is a kind of ‘mini black hole’ 10 times more massive than our Sun and located 1,600 light years from Earth, in the direction of the Ophiuchus constellation. There are also black holes so large that it is difficult to conceive of them, as in the case of TON 618 with 66 billion solar masses.
According to the current most accepted theory, for TON 618 to emerge, there must have been a star even larger than the giant black hole ever discovered. It is in these situations when the new theory of Chilean scientists makes sense. Supermassive black holes could be the result of the union of millions of stars bound by gravity in a nuclear star cluster.