Astronomers have found the closest black hole 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; the particularities of its orbit have made it possible to highlight the presence of an extremely massive object. So massive, in fact, that researchers 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 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 down these cosmic monsters in our galaxy, the Milky Way.

A great cosmic hide-and-seek game

To identify them, he seeks to identify binary systems, that is to say pairs of celestial bodies that orbit around a common center of gravity. In some cases, one of the duo members may be a black hole. They are then fascinating study objects for researchers, because they are real open-air laboratories that allow 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 are not jostling at the gate in our Milky Way. Or in any case, they know how to be discreet. Indeed, 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 so far, El-Badry and his troops have come up short until this recent discovery. ” My previous attempts have identified a whole menagerie of binary systems disguised as black holes, but this is the first time this search has paid off. “, he rejoices.

The closest black hole 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 objective is to build a gigantic 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 veritable scientific windfall in which El-Badry and his colleagues identified no less than 168,065 potential candidates. All 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 nicknamed Gaia BH1. All the data indeed indicate that the star evolves in a particularly 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 trajectory of the object and, finally, to determine the mass of its mystery 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.

… for the moment !

A record ultimately quite anecdotal, especially since we must take into account another much more interesting element; it is also the very first to have been 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 down the millions of black holes that the Milky Way is supposed to harbor.

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

But they only represent the tip of the iceberg; a larger population [de trous noirs dormants] probably hides 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 these already solid data to remove the last remaining doubts. It will then be necessary to relaunch the hunt for these sleeping monsters. The objective: to study more closely their still little known influence on the dynamics of the cosmos. For if they are as numerous as expected, the implications for modern cosmological models could be considerable.

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

The research paper is available here.

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