Sagittarius A*, the 4.3-million-solar-mass black hole at the center of our Milky Way Galaxy, was observed with the Atacama Large Millimeter/submillimeter Array (ALMA) as a part of the Event Horizon Telescope (EHT) campaign in 2017.
This artist’s illustration indicates where the modeling of the ALMA data predicts the hot spot to be and its orbit around Sagittarius A*. Image credit: ESO / M. Kornmesser / M. Wielgus / Event Horizon Collaboration.
“We think we’re looking at a hot bubble of gas zipping around Sagittarius A* on an orbit similar in size to that of the planet Mercury, but making a full loop in just around 70 minutes,” said Dr. Maciek Wielgus, a researcher at the Max Planck Institute for Radio Astronomy and a member of the EHT Collaboration.
“This requires a mind blowing velocity of about 30% of the speed of light.”
In April 2017, the EHT linked together eight existing radio telescopes worldwide, including ALMA, resulting in the recently released first ever image of Sagittarius A*, which is about 27,000 light-years away from Earth.
To calibrate the EHT data, Dr. Wielgus and colleagues used ALMA data recorded simultaneously with the EHT observations of Sagittarius A*.
To their surprise, there were more clues to the nature of the black hole hidden in the ALMA-only measurements.
By chance, some of the observations were done shortly after a burst or flare of X-ray energy was emitted from the center of our Galaxy, which was spotted by NASA’s Chandra Space Telescope.
These kinds of flares, previously observed with X-ray and infrared telescopes, are thought to be associated with so-called ‘hot spots’ — hot gas bubbles that orbit very fast and close to the black hole.
“What is really new and interesting is that such flares were so far only clearly present in X-ray and infrared observations of Sagittarius A*,” Dr. Wielgus said.
“Here, we see for the first time a very strong indication that orbiting hot spots are also present in radio observations.”
“Perhaps these hot spots detected at infrared wavelengths are a manifestation of the same physical phenomenon: as infrared-emitting hot spots cool down, they become visible at longer wavelengths, like the ones observed by ALMA and the EHT,” said Jesse Vos, a Ph.D. student at Radboud University.
The flares were long thought to originate from magnetic interactions in the very hot gas orbiting very close to Sagittarius A*, and the new findings support this idea.
“Now we find strong evidence for a magnetic origin of these flares and our observations give us a clue about the geometry of the process,” said Dr. Monika Mościbrodzka, an astronomer at Radboud University.
“The new data are extremely helpful for building a theoretical interpretation of these events.”
The data from ALMA and the GRAVITY instrument at ESO’s Very Large Telescope both suggest the flare originates in a clump of gas swirling around the black hole at about 30% of the speed of light in a clockwise direction in the sky, with the orbit of the hot spot being nearly face-on.
“In the future we should be able to track hot spots across frequencies using coordinated multiwavelength observations with both GRAVITY and ALMA — the success of such an endeavor would be a true milestone for our understanding of the physics of flares in the Galactic center,” said Dr. Ivan Marti-Vidal, an astronomer at the University of València.
The findings appear in the journal Astronomy & Astrophysics.
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M. Wielgus et al. 2022. Orbital motion near Sagittarius A*. Constraints from polarimetric ALMA observations. A&A 665, L6; doi: 10.1051/0004-6361/202244493
Source link: https://www.sci.news/astronomy/sagittarius-a-hot-spot-11224.html
