A bubble of hot gas orbits the Milky Way’s black hole

According to scientists, this hot spot orbits Sagittarius A* at 30% of the speed of light.

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Observations with the Atacama Large Millimeter/submillimeter Array ( ALMA ) have revealed signs of a “hot spot” orbiting Sagittarius A* , the black hole at the center of our galaxy.

“We think we’re seeing a hot bubble of gas zipping around Sagittarius A* in an orbit similar in size to that of the planet Mercury, but making a complete loop in only about 70 minutes! This requires an impressive speed of about the 30% of the speed of light!”, says in a statement Maciek Wielgus, from the Max Planck Institute for Radio Astronomy in Bonn (Germany), who has led this study, published in the journal Astronomy & Astrophysics .

The observations were made with ALMA , a radio telescope located in the Chilean Andes, co-owned by the European Southern Observatory (ESO), during a campaign by the Event Horizon Telescope (EHT) Collaboration to image black holes.

What is this gas point?

In April 2017, the EHT linked eight radio telescopes around the world, including ALMA , resulting in the first recently published image of Sagittarius A* . To calibrate the EHT data, Wielgus and his colleagues, who are members of the EHT Collaboration, used ALMA data recorded simultaneously with the Sagittarius A* EHT observations . To the team’s surprise, there were more clues to the nature of the hidden black hole in the ALMA measurements .

Coincidentally, some of the observations were made shortly after a burst or flare of X-ray energy was emitted from the center of our galaxy, which was detected by NASA’s Chandra Space Telescope. These types of flares, previously observed with X-ray and infrared telescopes, are thought to be associated with so-called “hot spots,” bubbles of hot gas that orbit very fast and very close to the black hole.

“What’s really new and interesting is that, until now, these types of flares were only clearly present in X-ray and infrared observations of Sagittarius A* . Here we see for the first time a very strong indication that hot spots in orbit are also present in observations made in the radio wave range,” says Wielgus, who is also affiliated with the Nicolaus Copernicus Astronomical Center (Poland) and the Black Hole Initiative at Harvard University (USA).

“Perhaps these hot spots detected at infrared wavelengths are a manifestation of the same physical phenomenon: as infrared-emitting hot spots cool, they become visible at longer wavelengths, such as those observed by ALMA and the EHT. “, adds Jesse Vos, a doctoral student at Radboud University (The Netherlands), who has also participated in this study.

The flares were long thought to originate from magnetic interactions in the very hot gas that orbits very close to Sagittarius A* , and the new findings support this idea. “We now find strong evidence for a magnetic origin of these flares and our observations give us a clue about the geometry of the process. The new data are extremely useful for building a theoretical interpretation of these events,” says co-author Monika Moscibrodzka of Radboud University.

ALMA enables the astronomical community to study the polarized radio emission from Sagittarius A* , 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 the hot spot and the environment in which it is embedded, including the magnetic field surrounding Sagittarius A* Relative to previous observations, this research provides stronger constraints. on the shape of this magnetic field, helping the astronomical community to discover the nature of our black hole and its surroundings.