Astronomers have found the black hole closest to the solar system

This observation could lead to the discovery of dozens of other black holes near the solar system.

An international team of astronomers has just made an unexpected but quite significant discovery by studying a star close to our Milky Way; its particular orbit has made it possible to highlight the presence of an extremely massive object. So massive, in fact, that scientists concluded it was probably a black hole. If so, it would be the closest black hole to the solar system – at least as far as we know.

This work was led by Kareem El-Badry. He is an eminent researcher affiliated with the prestigious Harvard-Smithsonian Center for Astrophysics and the Max Planck Institute for Astronomy. Among the list of associated specialists there are also residents of the Paris Observatory.

El-Badry is a skilled black hole hunter; in an interview with Universe Today, he explains that he has spent the last four years tracking these cosmic monsters in our galaxy, the Milky Way.

A fantastic cosmic hide and seek game

To identify them, he seeks to identify binary systems, that is, pairs of celestial bodies orbiting a common center of gravity. In some cases, one of the duo members can be a black hole. They are therefore fascinating objects of study for researchers because they are real open-air laboratories that enable the laws of physics to be subjected to the most demanding tests possible.

An artist’s impression of Gaia mapping the Milky Way. © ESA / ATG / ESO / S. Brunier

Unfortunately, these objects do not push at the gate of our Milky Way. Or at least they know how to be discreet. In fact, these binary systems are often extremely massive. For astronomers’ instruments, it is sometimes very difficult to tell the difference between a “normal” binary system and one that would host a black hole.

It is for this reason that El-Badry and his troops have so far fallen short until this recent discovery. ” My previous attempts have identified a whole menagerie of binary systems masquerading as black holes, but this is the first time this search has paid off. “, he rejoices.

The black hole closest to the solar system…

It all started with data reported by ESA’s Gaia observatory. It is one of the most important satellites for the scientific community. Its goal is to build a giant catalog of the cosmos. It does this by recording the movement of thousands of celestial bodies relative to the center of the Milky Way.

A true scientific windfall, in which El-Badry and his colleagues identified no less than 168,065 potential candidates. All of these celestial bodies had particular orbits, potentially compatible with the presence of a black hole.

Among them, they identified a particularly promising object: a G-type star – like our Sun – officially named Gaia DR3 4 373 465 352 415 301 632 and called Gaia BH1. Indeed, all the data indicate that the star is evolving on a special elliptical orbit near an extremely massive object.

To confirm this hypothesis, they pointed several of the most powerful instruments on the planet such as HIRES, FEROS, GMOS or even LAMOST directly at Gaia BH1. This arsenal allowed them to measure the intensity of the gravitational forces exerted on its orbit to confirm the object’s orbit and finally to determine the mass of its mysterious companion.

© ESO/L. Calcada

They concluded that the mass of this celestial body was about 10 solar masses and that it was contained in a relatively small space. These elements allowed them to conclude that it was indeed a black hole, the closest to our solar system.

… currently !

A record ultimately quite anecdotal, especially since we have to consider another much more interesting element; it is also the very first to be detected in our galaxy without relying on the intense radiation emitted by active black holes. If this detail is so important, it is because this work could henceforth serve as instructions for tracking the millions of black holes that the Milky Way is supposed to contain.

Models predict that the Milky Way contains about 100 million black holes ,” El-Badry tells Universe Today. ” But we observed only about twenty of them. And all the previous ones were what are called X-ray binaries, where the black hole consumes its twin star by emitting large amounts of X-rays “, he clarifies.

But they only represent the tip of the iceberg; a larger population [de trous noirs dormants] probably hiding in binary systems. The discovery of Gaia BH1 is a first step in this direction “, he rejoices.

The next step will therefore be to confirm this already solid data to remove the last remaining doubt. It then becomes necessary to restart the hunt for these sleeping monsters. The goal: to study more closely their still little-known influence on the dynamics of the cosmos. Because if they are as numerous as expected, the implications for modern cosmological models could be significant.

Either way, researchers will have to wait a little longer to get there. They rely heavily on the next set of data from Gaia, called GDR5. It will soon be published by ESA troops. Astronomers expect to find ten of similar systems, with all this implies for their work. It will therefore be necessary to see these publications to find out if BH1 was an isolated case or if, on the contrary, it was the first representative of a population of mysterious objects, but nonetheless very important to our understanding of the cosmos.

The research paper is available here.

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