Hot gas bubbles swirling around our supermassive black hole

‘Exciting’ hot bubble detected around Milky Way’s supermassive black hole

Astronomers have spotted signs of a “hot spot” orbiting Sagittarius A*, the black hole at the center of our galaxy.

Astronomers find signs of ‘hot spot’ orbiting Sagittarius A*

black hole
A black hole is a place in space where the gravitational field is so strong that not even light can escape. Astronomers classify black holes into three categories by size: micro black holes, stellar black holes, and supermassive black holes. Tiny black holes may be less massive than our sun, while supermassive black holes may be billions of times more massive than our sun.

“data-gt-translation-attributes=”[{” attribute=””>black hole at the center of our galaxy, using the Atacama Large Millimeter/submillimeter Array (The Orbit of the Hot Spot Around Sagittarius A*

This shows a still image of the supermassive black hole Sagittarius A*, as seen by the Event Horizon Collaboration (EHT), with an artist’s illustration indicating where the modeling of the ALMA data predicts the hot spot to be and its orbit around the black hole. Credit: EHT Collaboration, ESO/M. Kornmesser (Acknowledgment: M. Wielgus)

The observations were made with ALMA in the Chilean Andes, during a campaign by the Event Horizon Telescope (EHT) Collaboration to image black holes. ALMA is — a radio telescope co-owned by the European Southern Observatory (ESO). 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*. To calibrate the EHT data, Wielgus and his colleagues, who are members of the EHT Collaboration, used ALMA data recorded simultaneously with the EHT observations of Sagittarius A*. To the research team’s surprise, there were more clues to the nature of the black hole hidden in the ALMA-only measurements.

Using ALMA, astronomers discovered a hot bubble orbiting Sagittarius A*, the black hole at the center of our galaxy, at 30 percent the speed of light.

Occasionally, some observations were made shortly after a burst or flare of X-ray energy emanated from the center of our galaxy, which was caused by

Founded in 1958, NASA is an independent agency of the U.S. federal government following the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aerospace research.its vision is "Discover and expand knowledge for the benefit of humanity." Its core values ​​are "Safety, Integrity, Teamwork, Excellence and Inclusion."

“data-gt-translation-attributes=”[{” attribute=””>NASA’s Chandra X-ray Observatory. 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*. Here we see for the first time a very strong indication that orbiting hot spots are also present in radio observations,” says Wielgus, who is also affiliated with the Nicolaus Copernicus Astronomical Center, in Warsaw, Poland and the Black Hole Initiative at Harvard University, USA.

This video shows an animation of a hot spot, a bubble of hot gas, in the orbit of Sagittarius A*, a black hole 4 million times more massive than our sun, at our center

Milky Way
The Milky Way is the Milky Way that contains our solar system and is named for its appearance from Earth. It is a barred spiral galaxy containing an estimated 10-400 billion stars and is between 150,000 and 200,000 light-years in diameter.

“data-gt-translation-attributes=”[{” attribute=””>Milky Way. While the black hole (center) has been directly imaged with the Event Horizon Telescope, the gas bubble represented around it has not: its orbit and velocity are inferred from both observations and models. The team who discovered evidence for this hot spot — using the Atacama Large Millimeter/submillimeter Array (ALMA), in which First Image of Our Black Hole Sagittarius A*

This is the first image of Sgr A*, the supermassive black hole at the center of our galaxy. It’s the first direct visual evidence of the presence of this black hole. It was captured by the Event Horizon Telescope (EHT), an array that linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope. The telescope is named after the event horizon, the boundary of the black hole beyond which no light can escape. Credit: EHT Collaboration

ALMA allows astronomers to study polarized radio emission from Sagittarius A*, which can be used to unveil the black hole’s magnetic field. The team used these observations together with theoretical models to learn more about the formation of the hot spot and the environment it is embedded in, including the magnetic field around Sagittarius A*. Their research provides stronger constraints on the shape of this magnetic field than previous observations, helping astronomers uncover the nature of our black hole and its surroundings.

Milky Way Central Black Hole Location ALMA

This image shows the Atacama Large Millimeter/submillimeter Array (ALMA) looking up at the Milky Way as well as the location of Sagittarius A*, the supermassive black hole at our galactic center. Highlighted in the box is the image of Sagittarius A* taken by the Event Horizon Telescope (EHT) Collaboration. Located in the Atacama Desert in Chile, ALMA is the most sensitive of all the observatories in the EHT array, and ESO is a co-owner of ALMA on behalf of its European Member States. Credit: ESO/José Francisco Salgado (, EHT Collaboration

The observations confirm some of the previous discoveries made by the GRAVITY instrument at ESO’s Milky Way Wide Field View

Wide-field view of the center of the Milky Way. This visible light wide-field view shows the rich star clouds in the constellation of Sagittarius (the Archer) in the direction of the center of our Milky Way galaxy. The entire image is filled with vast numbers of stars — but far more remain hidden behind clouds of dust and are only revealed in infrared images. This view was created from photographs in red and blue light and forming part of the Digitized Sky Survey 2. The field of view is approximately 3.5 degrees x 3.6 degrees. Credit: ESO and Digitized Sky Survey 2. Acknowledgment: Davide De Martin and S. Guisard (

The team is also hoping to be able to directly observe the orbiting gas clumps with the EHT, to probe ever closer to the black hole and learn more about it. “Hopefully, one day, we will be comfortable saying that we ‘know’ what is going on in Sagittarius A*,” Wielgus concludes.

More information

Reference: “Orbital motion near Sagittarius A* – Constraints from polarimetric ALMA observations” by M. Wielgus, M. Moscibrodzka, J. Vos, Z. Gelles, I. Martí-Vidal, J. Farah, N. Marchili, C. Goddi and H. Messias, 22 September 2022, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202244493

The team is composed of M. Wielgus (Max-Planck-Institut für Radioastronomie, Germany [MPIfR]; Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Poland; Black Hole Project, Harvard University, USA [BHI]), M. Moscibrodzka (Department of Astrophysics, Radboud University, The Netherlands [Radboud]), J. Vos (Radboud), Z. Gelles (Center for Astrophysics | Harvard and Smithsonian Institutions and BHI, USA), I. Martí-Vidal (University of Valencia, Spain), J. Farah (Las Vegas, USA) Cambrais Observatory; University of California, Santa Barbara, USA), N. Marchili (ALMA Regional Center, INAF-Istituto di Radioastronomia, Italy and MPIfR), C. Goddi (Dipartimento di Fisica, Università degli Studi di di Cagliari, Italy and Universidade de São Paulo, Brazil) and H. Messias (ALMA Joint Observatory, Chile).

The Atacama Large Millimeter/Submillimeter Array (ALMA) is an international astronomy facility that is a partnership between ESO, the US National Science Foundation (NSF), and Japan’s National Institute of Natural Sciences (NINS) in collaboration with the Republic of Chile. ALMA is funded by ESO on behalf of its member countries, by NSF in partnership with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST), by NINS in partnership with the Academia Sinica (AS) in Taiwan and the Korea Institute of Astronomy and Space Sciences ( KASI). The construction and operation of ALMA is led by ESO on behalf of its member countries; the National Radio Astronomy Observatory (NRAO) managed by Associated Universities, Inc. (AUI) on behalf of North America; and the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides unified leadership and management of the construction, commissioning and operation of ALMA.

The European Southern Observatory (ESO) enables scientists around the world to discover the secrets of the universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to solve exciting problems and spread the fascination of astronomy — and foster international collaboration in astronomy. Founded in 1962, ESO is an intergovernmental organization and today has 16 member states (Austria, Belgium, Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, Netherlands, Poland, Portugal, Spain, Sweden, Switzerland, and the United Kingdom), as well as host countries Chile and Australia as strategic partners. ESO’s headquarters with its visitor center and planetarium ESO Supernova is located near Munich, Germany, while Chile’s Atacama Desert is a wonderful place with unique viewing sky conditions with our telescopes. ESO operates three observatories: La Silla, Paralal and Chajnantor. At Paranal, ESO operates the VLT and its VLT interferometer, as well as two survey telescopes, and VISTA operates the infrared and visible VLT survey telescopes. Paranal ESO will also host and operate the Cherenkov Telescope Array South, the largest and most sensitive gamma-ray observatory in the world. Together with international partners, ESO operates APEX and ALMA at Chajnantor, two facilities that can observe the sky in the millimeter and submillimeter range. At Cerro Armazones, near Paranal, we are building the “world’s largest eye in the sky” – ESO’s Very Large Telescope. Our office in Santiago, Chile supports our operations in the country and interacts with our Chilean partners and society.

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