Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have discovered signs of a “hot spot” orbiting Sagittarius A*, the black hole at the center of our galaxy. The discovery helps astronomers better understand the mysterious and dynamic environment of our supermassive black hole.
“We think we’re looking at a hot bubble that zips around Sagittarius A* with an orbit similar in size to the planet Mercury, but completes a full cycle in about 70 minutes. This requires an exciting speed of approx. 30% the speed of light,” said Maciek Wielgus of the Max Planck Institute for Radio Astronomy in Bonn, Germany, who led the research published today in Astronomy and Astrophysics.
The observations were made at ALMA in the Chilean Andes — a radio telescope jointly owned by the European Southern Observatory (ESO) — as part of a black hole imaging campaign organized by the Event Horizon Telescope (EHT) collaboration. In April 2017, EHT brought together eight existing radio telescopes around the world, including ALMA, resulting in the first recently released image of Sagittarius A*. To calibrate the EHT data, Wielgus and his colleagues, who are members of the EHT Collaboration, used ALMA data recorded concurrently with EHT observations of Sagittarius A*. To the team’s surprise, more clues about the nature of the black hole were hidden in the ALMA-only measurements.
Occasionally, some observations were made shortly after a burst or flare of X-ray energy emanated from the center of the Milky Way, discovered by NASA’s Chandra Space Telescope. Such flares, previously observed with X-ray and infrared telescopes, are thought to be associated with so-called “hot spots,” hot bubbles that orbit very fast and close to the black hole.
“What’s really novel and interesting is that such flares have so far only been clearly present in X-ray and infrared observations of Sagittarius A*. Here, for the first time, we see a very strong indication that orbits are also present in the radio Hotspot observations,” said Wielgus, who is also affiliated with the Nicholas Copernicus Astronomical Center in Poland and the Black Hole Project at Harvard University in the United States.
“Perhaps these hotspots detected at infrared wavelengths are manifestations of the same physical phenomenon: as infrared-emitting hotspots cool, they become visible at longer wavelengths, as observed by ALMA and EHT,” adds Jesse Vos , Ph.D. student at Radboud University in the Netherlands, who also participated in the study.
Flares have long been thought to originate from magnetic interactions in the very hot gas very close to Sagittarius A*, and the new findings support this idea. “Now that we have found strong evidence for the magnetic origin of these flares, our observations give us clues about the geometry of the process. The new data are very helpful in establishing a theoretical explanation for these events,” says co-author Monika Mościbrodzka. Radboud University.
ALMA allows astronomers to study Sagittarius A*’s polarized radio emissions, which can be used to reveal the black hole’s magnetic field. The team used these observations in conjunction with theoretical models to learn more about the formation of hotspots and the environments in which they are embedded, including the magnetic field around Sagittarius A*. Their study provides stronger constraints on the shape of this magnetic field than previous observations, helping astronomers shed light on the nature of our black hole and its surroundings.
These observations confirm some of the findings previously observed in the infrared by the GRAVITY instrument on ESO’s Very Large Telescope (VLT). Data from both GRAVITY and ALMA suggest that the flare originates from a cloud of gas swirling clockwise in the sky around the black hole at about 30% the speed of light, with the hotspot orbiting almost head-on.
“In the future, we should be able to use the coordinated multi-wavelength observations of GRAVITY and ALMA to track hotspots across frequencies – the success of this effort will be a real milestone in our understanding of the physics of flares at the center of the Milky Way,” said the University of Valencia in Spain. Ivan Marti-Vidal, co-author of the study.
The team also hopes to use the EHT to directly observe clumps of orbiting gas to probe closer to the black hole and learn more. “Hopefully one day we’ll be comfortable saying we ‘know’ what happened to Sagittarius A*,” Wielgus concluded.
The research is published in the paper “Orbital Motion Near Sagittarius A* – Constraints from Polarized ALMA Observations,” published in Astronomy and Astrophysics.
Examining supermassive black holes in our galaxy
M. Wielgus et al., Orbital motion near Sagittarius A*, Astronomy and Astrophysics (2022). DOI: 10.1051/0004-6361/202244493
Citation: Astronomers retrieved on September 23, 2022 from https://phys.org/news/2022-09-astronomers-hot-gas-swirling-milky.html supermassive black hole orbiting the Milky Way (2022, September 22 day) swirling hot bubbles
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