The center of our Milky Way is occupied by Sagittarius A*, a huge black hole that falls into the supermassive category. But this behemoth is not alone. It also coexists with other, much smaller black holes that appear at the end of the life cycle of stars. Their mass being roughly equivalent to that of a star, they have been soberly called stellar-mass black holes, and some studies suggest that our galaxy could contain billions of them. But between the two, there is a real statistical gap.
In theory, we should also find tintermediate mass black rous, or IMBH (pour Intermediate Mass Black Hole). But these tend to be conspicuous by their absence; they seem exceedingly rare and are very difficult to spot. Compared to supermassive black holes, the radiation and gravitational forces emanating from IMBHs are rather weak. Furthermore, unlike smaller ones, they tend to be rather isolated. They are almost never found near supernova remnants left by the cataclysmic death of stars, and they are rarely embedded in binary systems. All of these factors make it very difficult to detect these objects, which are also much less numerous in absolute terms.
The discovery of an IMBH is therefore an event extremely rare. To date, astronomers have found only about ten of them in the entire observable universe. And in our own galaxy, the record is even less flattering. Only a handful of objects could possibly fit this definition, and specialists have often hit a wall trying to confirm their status. The data are generally too ambiguous to be able to rigorously confirm that they are indeed intermediate-mass black holes.
That began to change two weeks ago, however, when a team from the prestigious Max Planck Institute identified the most promising candidate yet in the Milky Way—this time with very compelling data to back it up. A few days ago, researchers from the University of Cologne followed suit with similar—and potentially even more interesting—results.
A particularly mysterious star cluster
This new work concerns IRS 13a rather unusual star cluster that has long been a huge puzzle for specialists. When it was discovered 25 years ago, it was first considered a gigantic star, then a binary system, then a Wolf-Rayet star. This term refers to a transitional stage that some extremely hot, massive and luminous stars go through when they are near the end of their life cycle and are on the verge of going supernova.
More recently, more detailed observations have confirmed that it is in fact a star cluster. But this validation has not solved all the mysteries surrounding IRS 13, quite the contrary. Instead, it has brought to light a host of other mysteries, including a particularly thorny one.
For starters, it’s incredibly dense; it’s by far the most compact cluster ever observed in the Milky Way. Furthermore, it lies 0.1 light-years from Sagittarius A*, the titan at the heart of the galaxy. And this exceptional proximity poses a serious theoretical problem. Indeed, at this close distance, the gravitational forces are so intense that a cluster of this kind should theoretically not be able to remain coherent. It therefore seems to defy the laws of physics as they are established today.and to this day, no one has managed to explain how IRS 13 could resist the embrace of the supermassive black hole.
An intermediate black hole serving Sagittarius A*
To answer this question, the team of Florian Peißker, an astrophysicist at the University of Cologne in Germany, launched a new observation campaign. To solve the mystery, they looked at the dynamics of the cluster, that is, the way in which the stars and the clouds of gas and dust move relative to each other. They expected these movements to be more or less random, but they observed quite the opposite. In reality, all the objects engage in a surprisingly well-coordinated ballet.
This is anything but anecdotal, because according to the team, the coherence of the cluster and its singular dynamics necessarily imply the presence of another, more massive object. They therefore tried to locate the object in question, and this is where this work becomes really exciting.
At the center of the cluster, they detected a X-ray sourcewhich usually points to the presence of a highly energetic phenomenon. While searching for its source, they then observed a very rapidly rotating ring of ionized gas (about 130 km/s). It looks very much like an accretion disk—a vast disk of gas and dust superheated by the gravitational influence of a black hole. Finally, the team calculated the mass of this mysterious central element based on the trajectories of the other objects in IRS 13. They determined that it was of the order of 30,000 solar massesand there is only one type of object known or theorized that could check all of these boxes at once: Everything indicates that it is one of these famous intermediate-mass black holes.
« This fascinating star cluster has continually surprised the scientific community since its discovery some twenty years ago. “, Peißker said in the university’s press release. With these new high-resolution data, we can now confirm the composition of the constituent elements with an intermediate-mass black hole at the center. »
A step forward in understanding supermassive black holes
Further, more in-depth observations will be needed to confirm this interpretation of the results, but the case already seems very strong. And that’s great news, because this discovery could represent a major step forward in our understanding of the black hole cycle.
Indeed, while there are several promising theories, we don’t know exactly how supermassive black holes like Sagittarius A* are born and reach such gigantic masses. One of the most convincing scenarios is that they assimilate large quantities of matter and even other black holes during their life. This work on IRS 13 supports this theory; the cluster seems to be a small pantry that helps the behemoth to sustain itself. IRS 13 appears to be a key building block of our central black hole SgrA* ” explains Peißker.
It will therefore be very interesting to push these observations even further. IRS 13 will undoubtedly become a fabulous open-air laboratory which will allow astrophysicists to better understand what role this kind of object can play in the evolution of giant black holes. The other very exciting point is that this work offers an excellent lead to find more IMBHs: other representatives of this category are perhaps hidden in other star clusters near the supermassive black hole.
If so, this would allow astrophysicists to obtain even more valuable data to understand their behavior – with all that this implies for the global dynamics of the Universe. So all that remains is to wait for cutting-edge observatories like JWST or the ELT, the largest telescope in the world currently under construction in Chile, to turn their lenses on IRS 13 and its ilk.
The text of the study is available ici.
Source: www.journaldugeek.com
