On May 12, 2022, the very first image of the central black hole of our Galaxy, Sagittarius A* was unveiled. Researchers have since continued their studies on this supermassive star. And by observing data from the Alma radio telescope, they made a surprising discovery: a bubble of incandescent gas orbits around the black hole, at 30% of the speed of light! How to explain it?
On May 12, 2022, the very first image of the central black hole of our GalaxyGalaxy was revealed by theEvent Horizon Telescope (EHT). Sagittarius A* was visible for the first time, along with its accretion diskaccretion disk. The opportunity to learn more about this supermassive black holesupermassive black hole nearly 4 billion solar masses! Located in the heart of the Milky WayMilky Wayat 27,000 light yearslight years from Earth, Sagittarius A* will have given scientists difficulties: five years of hard work were necessary to put it into an image. Indeed, the observations on which it is based date from 2017, and were carried out by a network of eight radio telescopes, including theAtacama Large Millimeter/submillimeter Array (Alma), located at the European Southern Observatory (IT’SIT’S) in Chile.
But after having imaged it, researchers used Alma’s observations to deduce the properties of our black hole and its environment. And, lucky for them, they spotted a strange phenomenon there, detailed in a study by Astronomy & Astrophysics : and hotspothotspot orbiting at high speed all around Sagittarius A*! “We think we are looking at a gas bubble incandescentincandescent sliding around Sagittarius A* on a orbitorbit similar in size to that of the planet MercureMercure, but making a full turn in just about 70 minutes. This requires a mind-blowing velocity of around 30% of the speed of lightspeed of light ! », enthuses Maciek Wielgus in a press release from the ESO, first author of the study and astronomerastronomer au 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 modeling forecast data from Alma. © EHT Collaboration, ESO, M. Kornmesser, M. Wielgus
An eruption of Sagittarius A* ejected a bubble of plasma…
According to the study, this hot spot finds its explanation in the eruption of black holes. Indeed, the observations used by the researchers dated both April 6 and 7, 2017, and April 11, 2017. However, an eruption of the black hole Sagittarius A * occurred just before these last observations, detected in them X-raysX-rays speak space telescopespace telescope Chandra. The data collected by the researchers, curves of polarized light, then changed and they interpreted them as the generation of a hot spot spinning at high speed around the black hole. Because the change of curve of polarized light indicates a modification of the magnetic fieldsmagnetic fields surrounding the black hole.
And for researchers, this is proof that everything is played by magnetic fields! “Now we find evidence solidsolid for a magnetic origin of these eruptions, and our observations give us a clue to the geometry of the process. The new data is extremely useful in constructing a theoretical interpretation of these events.” explains Monika Mościbrodzka, co-author of the study and an astronomer at Radboud University. These black hole eruptions resemble those taking place on the surface of our starstarthe SoleilSoleilat the origin of polar aurorapolar aurora.
In the case of a black hole, the gazgaz hot which orbits very quickly around it forms an accretion disk. Within the disc, the mattermatter is so heated, to millions of degrees, that it changes into plasma, therefore into ionized and magnetized gas. Due to extreme temperature conditions, pressionpression, speed, which prevail in the disc, different magnetic fields are generated, which interact with each other and twist. When these fields meet, they can reconnect or reconfigure, leading to what is called magnetic reconnection. Part of theenergyenergy accumulated before reconnection is then ejected, whether in the form of X-rays, heatheat, or even directly from matter. And that’s what the researchers observed: a bubble of glowing gas, ” orbiting clockwise in an innermost region of the accretion flow”describes the study.
which then cooled! And that’s what the researchers saw.
Finally, these observations testify to a new phenomenon coming from the eruptions, unknown until now: the cooling of the plasma jets emitted by this eruption which 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-ray and infraredinfrared of Sagittarius A*. Here we see for the first time a very strong indication that orbiting hotspots are also present in radio observations.” explique Maciek Wielgus.
Because the fact that this gas bubble was observed in radio waves indicates a fairly 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 physical phenomenon: as soon as the hot spots emitting in the infrared cool down, they become visible in the wavelengthswavelengths longer, such as those observed by Alma and EHT”, adds Jesse Vos, study co-author and PhD student at Radboud University in the Netherlands. Subsequently, the researchers intend to focus even more on this phenomenon, in particular through observations with the EHT. “Hopefully we will one day be able to claim that we ‘know’ what is going on in Sagittarius A*”conclut Maciek Wielgus.