Collisions between massive stars could give rise to massive black holes

(ORDO NEWS) — The outcome of a collision between two giant stars is difficult to predict, but in a new, first-of-its-kind hydrodynamic simulation, a team of scientists from the University of Padua, Italy, has a number of possible exotic results of the collision.

One scenario involves the gradual formation of more and more massive black holes in “stellar cradles” where large stars are located very close to each other.

Astrophysicist Michela Mapelli will present modeling results and predictions on Monday, April 11, at the April meeting of the American Physical Society.

The Mapelli model provides a possible answer to the question about the origin of the gravitational wave event GW190521, which was registered in 2019 using the Advanced LIGO and Virgo detectors. The signal corresponding to this event had a characteristic shape indicating a collision between two black holes.

In this case, the masses of the original black holes should have been 85 and 66 solar masses, respectively. As a result of the collision, a black hole was formed with a mass of more than 140 masses of our star.

However, this version of the collision caused bewilderment among scientists. The resulting black hole had a mass larger than typical stellar-mass black holes formed from collapsed stellar cores, but smaller than supermassive black holes.

Such a mass falls straight into the “desert”, which is a mass range in which black holes have hardly been detected until now.

However, according to new hydrodynamic simulations by Mapelli and her team at the DEMOBLACK project, such a giant black hole could form when large stars in a densely populated “stellar nursery” collide.

The simulation starts with two stars, one of which lies on the main sequence and is a physically not deeply evolved star with a mass of about 40 solar masses.

Such a star is mainly composed of primordial hydrogen. The other star is more mature, about 60 solar masses, and has a compact helium core.

With some assumptions, these stars can collapse into a black hole with a mass of over 50 solar masses. And such black holes can, in turn, form binary systems and eventually merge. Repeated collisions and mergers can lead to the formation of black holes of large masses, ranging from 100 to 10,000 solar masses, Mapelli said.

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