As the Event Horizon Telescope collected data for its remarkable new image of the supermassive black hole of the Milky Way, Sagittarius A*, a legion of other telescopes, including three NASA X-ray space observatories, were also observing it (this was in April 2017). But it was using the Atacama Large Millimeter/submillimeter Array (ALMA) ground-based telescope that astronomers detected signs of a “hot spot” orbiting the planet. black hole supermassive It would be a bubble of very hot gas. Analysis of its behavior should help to better understand the dynamic environment of the object.
When the Event Horizon Telescope (EHT) observed Sagittarius A* in April 2017 to obtain the new image Recently revealed, scientists in the collaboration also observed the black hole with 8 facilities that detect different wavelengths of light.
Therefore, they collected X-ray data from: NASA’s Chandra X-ray Observatory, the Nuclear Spectroscopic Telescope Network (NuSTAR), and the Neil Gehrels Swift Observatory; radius of the East Asian Very Long Baseline Interferometer (VLBI) array and the global 3-millimeter VLBI array; Infrared images from the Atacama Large Millimeter/submillimeter Array (ALMA) telescope at the European Southern Observatory in Chile.
To calibrate the EHT data, Wielgus and his colleagues, members of the EHT Collaboration, used ALMA data from Sagittarius A* recorded simultaneously with the EHT observations. To the team’s surprise, there were many more clues to the nature of the black hole in the ALMA measurements alone. His discovery is the subject of a publication in the magazine astronomy and astrophysics.
See at the right time
while some black holes supermassives can be extremely active: they “eat up” large amounts of gas and dust and shine brightly in X-rays. Sagittarius A* is fairly quiet by comparison.
It is therefore by chance that the ALMA telescope, during this observation campaign for the EHT, surprised a burst or eruption of X-ray energy emitted from the center of the Earth. galaxybetween April 6 and 12, 2017. Scientists believe that these types of eruptions, previously observed with X-ray and infrared telescopes, are associated with so-called “hot spots”, hot gas bubbles that orbit very quickly, near of a black hole.
Wielgus, affiliated with the Nicolaus Copernicus Astronomical Center, Poland, and the Black Hole Initiative at Harvard University, USA, says in a release : “ What is really new and interesting is that such flares have so far only been clearly present in X-ray and infrared observations of Sagittarius A*. Here we see for the first time a very strong indication that orbiting hotspots are also present in radio observations. “.
Jesse Vos, a PhD student at Radboud University in the Netherlands who was also involved in this study, hypothesizes to explain this radio observation that the behavior of these hot spots could be similar to a manifestation of a known physical phenomenon. : “ As infrared-emitting hotspots cool, they become visible at longer wavelengths, such as those observed by ALMA and the EHT. “.
A bubble of space gas to explain the mysteries of black holes
Remember that black holes are objects where gravity is so strong that nothing, not even light, can escape. The event horizon, or “surface” of the black hole, marks this limit of no return, while the accretion disk is made up of the matter that orbits it.
Astronomers have long thought that the flares come from magnetic interactions within matter in this accretion disk, including very hot gas, with the magnetic field surrounding the black hole. The new findings support this idea. Co-author Monika Mościbrodzka of Radboud University notes: We now find strong evidence for a magnetic origin of these eruptions and our observations give us a clue about the geometry of the process. The new data is extremely useful in building a theoretical interpretation of these events. “.
ALMA allows astronomers to study the polarized radio emissions from Sagittarius A*, which can be used to discover the black hole’s magnetic field. The team used these observations with theoretical models to learn more about the formation of the hotspot and the environment in which it is embedded, including the magnetic field around the black hole. This study provides much stronger constraints on the shape of this magnetic field than previous observations, helping astronomers understand the nature of the Milky Way’s central black hole and its surroundings.
Maciek Wielgus of the Max Planck Institute for Radio Astronomy in Bonn, Germany, who led the study, explains: We think we’re dealing with a bubble of hot gas that revolves around Sagittarius A* in an orbit similar in size to the planet Mercury, but completing a full cycle in only about 70 minutes. This requires mind-boggling speed of about 30% of the speed of light! “.
Indeed, the observations confirm some of the earlier discoveries made with the GRAVITY instrument on ESO’s Very Large Telescope (VLT), which observes in the infrared. Data from GRAVITY and ALMA suggest that the eruption originated from this clump of gas swirling around the black hole in a clockwise direction in the sky, with the hotspot’s orbit nearly head-on.
Ivan Marti-Vidal, from the University of Valencia in Spain, co-author of the study, adds: In the future, we should be able to track hotspots across frequencies using coordinated multi-wavelength observations with GRAVITY and ALMA; the success of such an effort would be a real milestone in our understanding of the physics of flares at the galactic center. “.
The team now plans to try to directly observe the orbiting clumps of gas with the EHT, to probe the supermassive black hole as closely as possible and determine its dynamical characteristics, allowing its evolution to be predicted. Wielgus concludes: Hopefully one day we can say that we ‘know’ what is happening in Sagittarius A* “.