Galaxy clusters consist of a few hundred to several hundred thousand galaxies associated with gravity and are the largest astrophysical objects found in the universe. It is in the heart of one of them, RBS 797 galaxy cluster located 3.9 billion light-years from Earth, that four giant cavities have recently been discovered: areas mysteriously devoid of matter located about 45,000 light-years from the center of the cluster. .
Excavated thanks to NASA’s Chandra X-ray Observatory, they are the subject of a study published December 20, 2021 in the journal The Astrophysical Journal. The origin of these cavities remains a mystery to the authors of this research: only two scenarios could explain such vacuum zones, which both involve eruptions of black holes and are currently impossible to determine. This is at least the first time that such a phenomenon has been observed.
At the origin of this phenomenon, the eruption of black holes
How can such an amount of substance be “blown away”? The answer lies at the heart of these astrophysical objects that are supermassive black holes. They are located at the center of large galaxies, even at the center of the largest structures in the universe, galaxy clusters.
These black holes emit rays of matter and plasma along their magnetic axis so powerful that they then push all the nearby substance back and then create vacuum zones: this is called the eruption of black holes. Like a volcano, these eruptions are irregular, interrupted by quiet periods. This is exactly what we observe with the supermassive black hole Sagittarius A * at the center of our galaxy, the Milky Way.
Galaxy clusters consist of a few hundred to several hundred thousand galaxies associated with gravity and are the largest astrophysical objects found in the universe. It is in the heart of one of them, RBS 797 galaxy cluster located 3.9 billion light-years from Earth, that four giant cavities have recently been discovered: areas mysteriously devoid of matter located about 45,000 light-years from the center of the cluster. .
Excavated thanks to NASA’s Chandra X-ray Observatory, they are the subject of a study published December 20, 2021 in the journal The Astrophysical Journal. The origin of these cavities remains a mystery to the authors of this research: only two scenarios could explain such vacuum zones, which involve both outbreaks of black holes and for the time being it is impossible to decide. This is at least the first time that such a phenomenon has been observed.
At the origin of this phenomenon, the eruption of black holes
How can such an amount of substance be “blown away”? The answer lies at the heart of these astrophysical objects that are supermassive black holes. They are located at the center of large galaxies, even at the center of the largest structures in the universe, galaxy clusters.
These black holes emit rays of matter and plasma along their magnetic axis so powerful that they then push all the nearby substance back and then create vacuum zones: this is called the eruption of black holes. Like a volcano, these eruptions are irregular, interrupted by quiet periods. This is exactly what we observe with the supermassive black hole Sagittarius A * at the center of our galaxy, the Milky Way.
Thus, the cavities observed by Chandra may be caused by such a phenomenon. But the peculiarity of the study we are talking about here is another place: this time it is not two but four holes of matter that the researchers observed. These cavities were discovered thanks to observations made with the European VLBI network. LThe researchers had first found two point radio sources, separated by about 250 light-years in RBS 797. Then it was five days of observation from Chandra that made it possible to identify the four cavities with precision.
Four cavities and two scenarios
These cavities are formed as a symmetry figure because they are located at the same distance from the center of the galaxy, that is, between 17 and 81 thousands of light-years with one pair oriented east-west and the other north-south, as the researchers describe in their study: “The other two depressions are almost perpendicular to the larger E – W cavities and almost the same projected distance du active core of the galaxy (Between 5.5kpc and 27 kpc; kpc corresponds to “kiloparsec”, knowing that a parsec is worth 3.26 light-years, ed.note) “.
The four cavities are symmetrical with respect to the center of the galaxy cluster. CRstarsay: NASA / CXC / Univ. of Bologna / F. Ubertosi
The researchers’ latest discovery has not yet been fully explained, or rather its origins remain indefinite: two scenarios may be the cause of these four voids. “As Francesco Ubertosi from the University of Bologna in Italy reminds us in a press release from NASA, which led the Chandra study,”noneU.S soaps what is a pair of cavities, but what happens when a galaxy cluster has two pairs in very different directions? “.
According to the researchers, there are only two options. Either a black hole would have erupted before it changed direction to break out again. Either there would be a few black holes in the circuit. “If there is only one black hole responsible for these four cavities, then we will have to trace the history of its activity. The key questions are how quickly the orientation of the jets changed and whether it is related to the environment in the galaxy cluster or to the physics of the black hole itself. Or even a combination of the two “, said Fabrizio Brighenti, co-author and also researcher at the University of Bologna.
If there really are two black holes, they are is destined to merge
However, through analysis of Chandra’s X-ray data, the researchers were able to establish in their study that “the four cavities are the same age, from about 10 to 50 millions of years. That the age difference between the two explosions is maximum 10 million years “. An age difference that seems significant, but on the scale of black holes, it represents only a short duration. This result then favors the thesis of a few black holes at the origin of these bubbles.
But even though it is actually two different black holes that came into an eruption, the probability of them emitting so much substance remains very low, making the observation of such a phenomenon almost miraculous. “Our best idea is that a couple of supermassive black holes led to a couple of cavity pairs,” said Myriam Gitti, co-author of the study and researcher at the University of Bologna. “Although we believe that supermassive black holes can form binary systems, it is extremely rare for both to be observed in an active phase. In this sense, the discovery of two nearby active black holes that create cavities in RBS 797 is extraordinary. . “
Further investigations are underway to determine which scenario is the correct one, as the investigation concludes: “With the upcoming deep VLBI study of the core of the RBS 797 cluster, it will be possible to provide a definitive answer to the origin of the two perpendicular explosions discovered with Chandra. “ But one thing is for sure: if there are actually a few black holes that are at the origin of these cavities, their trajectory would be the closest that has ever been discovered, and these should merge in the future by generating huge amounts of gravitational waves, after gradually spiraling towards each other.