Using the Atacama Large Millimeter / submillimeter Array (ALMA), astronomers have identified signs of a “hot spot” orbiting Sagittarius A *, the black hole at the center of our galaxy. The discovery helps astronomers better understand the enigmatic and dynamic environment of our supermassive black hole.
“We think we are watching a bubble of hot gas whizzing around Sagittarius A * on an orbit similar in size to the planet Mercury, but completing a full circle in about 70 minutes. This requires an astounding speed of about 30% of the speed of light, “says Maciek Wielgus of the Max Planck Institute for Radio Astronomy in Bonn, Germany, who conducted the study published today in Astronomy and astrophysics.
The observations were made with ALMA in the Chilean Andes, a radio telescope co-owned with the European Southern Observatory (ESO), during an Event Horizon Telescope (EHT) collaboration campaign for the image of black holes. In April 2017, the EHT linked together eight existing radio telescopes around the world, including ALMA, resulting in the first-ever image of the recently released Sagittarius A *. To calibrate the EHT data, Wielgus and his colleagues, who are members of the EHT Collaboration, used the ALMA data recorded simultaneously with the EHT observations of Sagittarius A *. To the team’s surprise, there were more clues to the nature of the hidden black hole in ALMA’s measurements alone.
By chance, some of the observations were made shortly after an explosion or flash of X-ray energy was emitted from the center of the galaxy, which was detected by NASA’s Chandra Space Telescope. This type of flare, previously observed with X-ray and infrared telescopes, is thought to be associated with so-called “hot spots” – hot gas bubbles that orbit very quickly and close to the black hole.
“What’s really new and interesting is that such flares were so far clearly only present in X-ray and infrared observations of Sagittarius A *. Here, we see for the first time a very strong indication that orbiting hot spots are also present in the radio observations, ”says Wielgus, who is also affiliated with the Nicolaus Copernicus Astronomical Center, Poland and the Black Hole Initiative at Harvard University, in the United States.
“Perhaps these hot spots detected at infrared wavelengths are a manifestation of the same physical phenomenon: when the hot spots that emit infrared cool, they become visible at longer wavelengths, such as those observed by ALMA and the EHT, ”adds Jesse Vos, a PhD student at Radboud University in the Netherlands who was also involved in this study.
The flares have long been thought to come from magnetic interactions in very hot gas orbiting very close to Sagittarius A *, and new findings support this idea. “We now find strong evidence of the magnetic origin of these flares and our observations give us a clue to the geometry of the process. The new data are extremely useful for building a theoretical interpretation of these events,” says co-author Monika Mościbrodzka of Radboud University. .
ALMA allows astronomers to study the polarized radio emission of Sagittarius A *, which can be used to reveal 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 in which it is embedded, including the magnetic field around Sagittarius A *. Their research provides stronger constraints on the shape of this magnetic field than previous observations, helping astronomers discover the nature of our black hole and its surroundings.
The observations confirm some of the earlier findings made by the GRAVITY instrument at ESO’s Very Large Telescope (VLT), which it observes in the infrared. The data from GRAVITY and ALMA both suggest that the glow originates in a cluster of gas that swirls around the black hole at about 30% of the speed of light clockwise in the sky, with the orbit of the hot spot almost frontally.
“In the future we should be able to track hotspots across frequencies using multi-wavelength coordinated observations with both GRAVITY and ALMA: the success of such a feat would be a real milestone for our understanding of the physics of glow in the galactic center. “says Ivan Marti-Vidal of the University of Valencia in Spain, co-author of the study.
The team also hopes to be able to directly observe the orbiting clumps of gas with the EHT, to probe ever closer to the black hole and learn more. “Hopefully one day we will be comfortable saying that we ‘know’ what’s going on in Sagittarius A *,” concludes Wielgus.
This research was presented in the paper “Orbital motion near Sagittarius A * —Constraints from polarimetric ALMA observations” to appear in Astronomy and astrophysics.
By examining the supermassive black hole in our galaxy
M. Wielgus et al, Orbital motion near Sagittarius A *, Astronomy and astrophysics (2022). DOI: 10.1051 / 0004-6361 / 202244493
Citation: Astronomers detect hot gas bubbles swirling around the Milky Way’s supermassive black hole (2022, September 22) recovered on September 23, 2022 from https://phys.org/news/2022-09-astronomers-hot-gas- swirling-milky. html
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