While studying the supermassive black hole at the center of our galaxy, Sagittarius A*, researchers made a strange discovery: a bubble of glowing gas spinning around it at a very high speed! A phenomenon that is explained by the eruption of black holes.
On May 12, 2022, the first image of our central black hole GalaxyGalaxy was revealed byevent horizon telescope (EHT). Sagittarius A* was visible for the first time, as well as its accretion diskaccretion disk. Located in the heart of the Milky WayMilky Wayin 27,000 Light yearsLight years From Earth, Sagittarius A* will have given scientists a hard time: it took five years of hard work to capture it in an image. In fact, the observations on which it is based date back to 2017 and were made by a network of eight radio telescopesradio telescopesincluding L’Atacama Large Millimeter/submillimeter Array (Alma), located at the European Southern Observatory (IT’SIT’S) in Chile.
From these Alma observations, researchers are trying to deduce the properties of our black hole and its environment. And, lucky for them, they detected a strange phenomenon there, detailed in a study by astronomy and astrophysics : a access pointaccess point orbiting high speedspeed all around the Sagittarius A* ! “We believe that we are facing a gas bubble incandescentincandescent gliding around Sagittarius A* in a orbitorbit similar in size to the planet Mercury, but making a complete rotation in only about 70 minutes. This requires mind-blowing speed of around 30% of the speed of lightspeed of light ! », enthuses Maciek Wielgus in a press release from ESO, first author of the study and astronomerastronomer a Max Planck Institute for RadioRadio astronomy in Bonn, Germany.
The supermassive black hole Sagittarius A*, imaged by the Event Horizon Telescope Collaboration (EHT), along with an artist’s impression of the location of the hotspot and its orbit around the black hole, based on Alma modeling forecast data. © Collaboration EHT, ESO, M. Kornmesser, M. Wielgus
The center of the galaxy has erupted
According to the study, this hot spot finds its explanation in the eruption of black holes. In fact, the observations used by the researchers date from April 6-7, 2017, and April 11, 2017. However, a black hole eruption Sagittarius A* occurred just before these latest sightings, detected in the X-raysX-rays speak space telescopespace telescope Chandra. The data collected by the researchers, curves of polarized light, then changed and interpreted as the generation of a hot spot spinning at high speed around the black hole. Because the change in the curve of polarized light indicates a modification of the magnetic fieldsmagnetic fields surrounding the black hole.
And for the researchers, this is proof that everything is played for magnetic fields ! “We now find strong evidence for a magnetic origin of these flares, and our observations give us a clue about the geometry of the process. The new data is extremely helpful in building a theoretical interpretation of these events.” explains Monika Mościbrodzka, a co-author of the study and an astronomer at Radboud University. These black hole flares resemble those that take place on the surface of our starstarthe Sun, at the origin of northern lightsnorthern lights.
in the case of a black holethe gasgas rapidly orbiting around it forms an accretion disk. Inside the disk, mattermatter it heats up so much, to millions of degrees, that it transforms into plasma, therefore into ionized and magnetized gas. Due to extreme temperature conditions, PressurePressure, speed, prevailing in the disk, different magnetic fields are generated, which interact with each other and twist. When these fields meet, they can be reconnected or reconfigured, leading to what is called a magnetic reconnection. Part ofEnergyEnergy accumulated before the reconnection is expelled, either in the form of X-rays, heatheat, or even directly from the matter. And that’s what the researchers observed: a glowing gas bubble.” orbiting clockwise in a region more internal to the accretion flow.describes the study.
These observations attest to the cooling of the plasma emitted during the eruption.
Finally, in addition to indicating an eruption of Sagittarius A*, these observations testify to a new phenomenon: the cooling of the plasma jets emitted by this eruption that remain in orbit around the black hole. “What is really new and interesting is that such flares have so far only been clearly present in X-rays and infraredinfrared of Sagittarius A*. Here we see for the first time a very strong indication that orbiting hot spots are also present in radio observations.” explains Maciek Wielgus.
In fact, the fact that this gas bubble has been observed in radio waves indicates a rather low temperature, these waves being much less energetic than X-rays or infrared. “Perhaps these hot spots detected under infrared waves are a manifestation of the same phenomenon physicalphysical : As soon as hot spots emitting in the infrared cool down, they become visible in the wavelengthswavelengths longer, like those observed by Alma and EHT,” adds Jesse Vos, a co-author of the study and a doctoral student at Radboud University in the Netherlands. Subsequently, the researchers intend to further focus on this phenomenon, in particular by observations with the EHT. “Hopefully one day we can say we ‘know’ what’s going on in Sagittarius A*”concludes Maciek Wielgus.