Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have detected signs of a “hot spot” orbiting around Sagittarius A*, the black hole at the center of our galaxy. This discovery helps astronomers understand the mysterious and dynamic environment of our supermassive black hole.
“We think we’re looking at a hot bubble of gas orbiting Sagittarius A* in an orbit similar in size to Mercury, but making a full loop in only about 70 minutes. This requires a brain to travel at about 30% of the speed of light,” he says. Masek Wilgus of the Max Planck Institute for Radio Astronomy in Bonn, Germany, who led the study published today in Astronomy and astrophysics.
The observations were made using ALMA in the Chilean Andes – a radio telescope owned by the European Southern Observatory (ESO) – during a campaign by the Event Horizon Telescope (EHT) Collaboration to Photograph Black Holes. In April 2017, the EHT connected eight radio telescopes located around the world, including ALMA, resulting in the first recently released image of Sagittarius A*. To calibrate the EHT data, Wielgus and colleagues, members of the EHT Collaboration, used ALMA data recorded in conjunction with the EHT observations of Sagittarius A*. To the team’s surprise, there was more clues to the nature of the black hole hidden in ALMA’s measurements alone.
By chance, some observations were made shortly after a burst or glow of X-ray energy was emitted from the galactic center, which was spotted by NASA’s Chandra Space Telescope. These types of flares, previously observed with X-ray and infrared telescopes, are believed to be associated with so-called “hot spots,” hot gas bubbles that rotate very quickly and close to the black hole.
“What is really new and exciting is that such flares have so far only been clearly present in X-ray and infrared observations of the A* arc. Here, we see for the first time a very strong indication that orbital hotspots are also present in radio,” says Weljus. which also belongs to the Nicholas Copernicus Astronomical Center in Poland and the Black Hole Initiative at Harvard University in the United States”.
“These hot spots detected at infrared wavelengths may be a manifestation of the same physical phenomenon: As infrared hot spots cool, they become visible at longer wavelengths, such as those observed by ALMA and EHT,” adds Jesse Voss. , Ph.D. A student at Radboud University in the Netherlands, who was also involved in this study.
The flares have long been thought to arise from magnetic interactions in the superheated gas that orbits near arc A*, and the new results support this idea. “We have now found strong evidence for a magnetic origin for these flares and our observations give us a clue about the engineering of the process. The new data are very useful for building a theoretical explanation for these events,” says co-author Monika Mościbrodzka from Radboud University.
ALMA allows astronomers to study the polarized radio emission from Sagittarius A*, which can be used to detect the black hole’s magnetic field. The team used these observations along with theoretical models to learn more about the formation of the hot spot and the environment within it, including the magnetic field around the A* arc. Their research provides stronger constraints on the shape of this magnetic field than previous observations, helping astronomers reveal the nature of our black hole and its surroundings.
The observations confirm some previous discoveries made by the GRAVITY instrument on ESO’s Very Large Telescope (VLT), which monitors infrared radiation. Data from GRAVITY and ALMA indicate that the glow originates in a mass of gas orbiting the black hole at about 30% the speed of light in a clockwise direction in the sky, facing roughly the hotspot’s orbit. .
“In the future, we should be able to track hotspots across frequencies using coordinated multi-length observations using both GRAVITY and ALMA – the success of such an endeavor will be a real milestone for our understanding of the physics of flares at the galactic center,” co-author Ivan Marti Vidal of the University of Valencia in Spain.
The team also hopes to be able to observe masses of orbital gases using the EHT, to find out more about the black hole and learn more about it. We hope one day we will feel comfortable saying we ‘know’ what’s going on in arc A*, concludes Wilgus.
This research is presented in the paper “Orbital Motion near Arc A* – Constraints from ALMA Polarization Observations” to appear in Astronomy and astrophysics.
Examining the supermassive black hole in our galaxy
Wilgus et al., Orbital Motion near Sagittarius A*, Astronomy and astrophysics (2022). DOI: 10.1051 / 0004-6361 / 202244493
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