Astronomers have discovered signs of a 'hot spot' near Sagittarius A*, the center of our galaxy.
Using the ATacama Large Millimeter/Submillimeter Array (ALMA), astronomers have discovered signs of a 'hot spot' orbiting Sagittarius A*, the star at the center of our galaxy. The finding helps us better understand the mysterious and dynamic environment of our supermassive black hole.
“We’re seeing a hot bubble of gas zipping around Sagittarius A* on an orbit similar in size to that of the planet Mercury, but making a complete loop in just over 70 minutes,” says Maciek Wielgus of the Max Planck Institute for Radio Astronomy in Bonn, Germany. The study was published today (September 22, 2022) in the journal Astronomy & Astrophysics.
This is a still image of the Event Horizon Collaboration (EHT) supermassive black hole Sagittarius A*, with an artist's illustration indicating where the ALMA data forecasts the hot spot to be and its orbit around the black hole. (Acknowledgment: M. Wielgus)
ALMA is a co-owned by the European Southern Observatory (ESO) to record black holes. In April 2017, Wielgus and his colleagues used ALMA data to calibrate the EHT data of Sagittarius A*, which was recently released.
Using ALMA, astronomers have discovered a hot gas bubble around Sagittarius A*, the center of our galaxy, at 30% of the speed of light.
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 discovered by NASA's Chandra X-ray Observatory. These kinds of flares, previously observed with X-ray and infrared telescopes, are thought to be related to so-called'hot spots,' hot gas bubbles that orbit very fast and near the black hole.
„What is really new and fascinating is that such flares were previously only noticeable in X-ray and infrared observations of Sagittarius A*. Here we see for the first time that orbiting hot spots are also visible 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 depicts a hot spot, a bubble of hot gas, in orbit around Sagittarius A*, a black hole four million times larger than our Sun that resides at the center of our Milky Way. Both observations and models are based on the assumption that the gas bubble orbits very close to the black hole's boundary or "event horizon."
As shown in this animation, the astronomers who discovered the hot spot anticipate the black hole to become dimmer and brighter as it passes through the hole. Additionally, they can infer that the gas bubble takes 70 minutes to complete an orbit, rendering its velocity at an astounding 30% of the speed of light.
Credit: EHT Collaboration, ESO/L. Calçada (Acknowledgment: M. Wielgus)
Jesse Vos, a PhD student at Radboud University in the Netherlands, believes these infrared hot spots are a result of the same physical phenomenon. They become visible at longer wavelengths as they cool down, like the ones observed by ALMA and the EHT.
The new findings support our assumption that these flares originated from magnetic interactions in a very hot gas orbiting very close to Sagittarius A*. “Now we have strong evidence for a magnetic origin of these flares, and our observations give us a clue about the processes,” says co-author Monika Moscibrodzka of Radboud University.
This is the first image of Sgr A*, the massive black hole at the center of our galaxy. This is the first direct visual evidence of this black hole's existence using the Event Horizon Telescope (EHT), a telescope that connected eight existing terrestrial radio observatories into a single "Earth-sized" virtual telescope. The event horizon is the boundary of the black hole beyond which no light can escape.
ALMA allows astronomers to investigate polarized radio emission from Sagittarius A*, which can be used to investigate the black hole's magnetic field. These findings were combined with theoretical models to explore the formation of the hot spot and the environment it is embedded in, including the magnetic field around Sagittarius A*.
The Atacama Large Millimeter/submillimeter Array (ALMA) is shown in the box, along with the location of Sagittarius A*, the most powerful black hole at Earth's galactic center, by the Event Horizon Telescope (EHT) Collaboration. ALMA is the most sensitive observatory in the Atacama Desert in Chile, and ESO is a co-owner of ALMA on behalf of its European Member States.
The observations confirm several previous findings made by the GRAVITY instrument at ESO's Very Large Telescope (VLT), which detects in the infrared. Both data from GRAVITY and ALMA indicate that the flare originates in a clump of gas wrapping 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 almost face-on.
The success of such a measure would be a significant milestone for our understanding of the structure of flares in the Galactic center, according to Ivan Marti-Vidal of the University of València in Spain.
This wide-field view of the Milky Way's center is created by ESO and the Digitized Sky Survey 2. The whole image is covered with large numbers of stars, although many more are hidden beneath clouds of dust and are only revealed in infrared photographs.
The team is hoping to be able to observe the EHT orbiting gas clumps, to investigate even further closer to the black hole and learn more about it. “We hope that one day, we will be comfortable saying that we 'know' what is happening in Sagittarius A*.
M. Wielgus, M. Moscibrodzka, J. Vos, I. Mart-Vidal, J. Farah, N. Marchili, C. Goddi, and H. Messias, 22 September 2022, Astronomy & Astrophysics. DOI: 10.1051/0004-6361/202244493
M. Wielgus (MPIfR) (Radboud University, The Netherlands, USA) and Z. Gelles (Center for Astrophysics | Harvard & Smithsonian, USA) J. Farah (Las Cumbres Observatory, USA; University of California, Santa Barbara, USA), C. Goddi (Dipartimento di Fisica, Universidade de So Paulo, Brazil)
The Atacama Large Millimeter/Submillimeter Array (ALMA) is a partnership between ESO, the National Science Foundation of Canada (NSF) and the National Institutes of Natural Sciences (NINS) of Japan on behalf of its Member States; by ESO in partnership with the Academia Sinica in Taiwan and the Korea Astronomical and Space Science Institute (KASI) on behalf of East Asia.
The European Southern Observatory (ESO) is a non-governmental organization that helps scientists around the world discover the mysteries of the universe for the benefit of everyone. ESO's headquarters and its visitor center, the ESO Supernova, are located near Munich in Germany, while the Chilean Atacama Desert, a spectacular spot to observe the sky, is home to ESO's extreme large telescope.