Black hole debate settled? Stellar-mass black holes found at the heart of the Milky Way’s largest star cluster

Omega Centauri is a huge star cluster in the constellation Centauri, containing nearly 10 million stars. Researchers have long noticed that stars near the center of Omega Centauri are moving faster than expected. But it is unclear whether this is caused by an “intermediate mass” black hole (IMBH) with a mass of 100,000 times the mass of the sun, or by a cluster of “stellar mass” black holes with a mass only a few times the mass of the sun.

A cluster of black holes is expected to form at the center of Omega Centauri due to stellar evolution. But astronomers believe that most of them will be ejected by slingshot interactions with other stars. Therefore, mid-MBH bores are starting to look more and more like the favored solution. This scenario seems more likely when new evidence recently emerged suggesting that fast-moving stars near the center of Omega Centauri may need to interact with intermediate-mass black holes to reach such high velocities.

Intermediate-mass black holes (IMBHs) excite astronomers because they may be the “missing link” between stellar-mass black holes and supermassive black holes. Stellar mass black holes are formed from the death of massive stars and have been discovered using a variety of different techniques. Supermassive black holes exist at the centers of large galaxies and weigh millions to billions of times the mass of the Sun. We currently do not know how supermassive black holes form, or whether they begin life as stellar-mass black holes. Finding intermediate-mass black holes could solve this cosmic puzzle.

New research involving the University of Surrey takes another look at the unusual speed of the star at the center of Omega Centauri, but this time, it uses a new piece of data. For the first time, researchers have combined the unusual velocity data with new data on the pulsar’s acceleration. Pulsars, like black holes, are formed from dying stars. They weigh twice the mass of the sun, are only 20 kilometers in diameter, and rotate 700 times per second. As they spin, they emit radio waves along their axis of rotation, like a spinning top. Radio beams sweep across the Earth like a beacon, allowing us to detect them.

Pulsars are natural clocks that are nearly as accurate as atomic clocks on Earth. By carefully measuring changes in the pulsar’s rotation rate, astronomers can calculate how the pulsar accelerates and thereby directly detect the strength of the gravitational field at the center of Omega Centauri. Combining these new acceleration measurements with stellar velocities, researchers from the Annecy-le-Vieux Laboratoire de Physique Théorique LAPTh in Surrey, Canary Institute of Astronomy (IAC, Spain) and Annecy (France) were able to distinguish IMBH and a swarm of black holes, favoring the latter.

Study co-author Professor Justin Reid from the University of Surrey said:

“The search for elusive intermediate-mass black holes continues. There may still be a black hole at the center of Omega Centauri, but our work suggests it must be less than about six thousand times the mass of the Sun and living with a population of stars. However, It’s very likely that we will soon find more and more pulsars accelerating, allowing us to observe the centers of dense star clusters and search for black holes more precisely than ever before.

Andr’es Bañares-Hernández, lead author of the IAC study, said:

“We have long known that supermassive black holes exist at the center of the Milky Way, and smaller stellar-mass black holes exist within the Milky Way. However, the idea that intermediate-mass black holes could bridge the gap between these extremes has not yet been proven.”

“By studying Omega Centauri – the remnant of a dwarf galaxy – we have been able to refine our methods and take a step forward in understanding whether such black holes exist and what role they might have played in the evolution of star clusters and galaxies. step.

“Pulsar formation is also an active area of ​​research, as a large number of pulsars have been detected recently. Omega Centauri is an ideal environment to study models of pulsar formation, and this is the first time we have been able to do this in our analysis.”