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Astronomers have shown the first image of a black hole in the center of our galaxy – ScienceDaily

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Today, at simultaneous press conferences around the world, including at the headquarters of the European Southern Observatory (ESO) in Germany, astronomers presented the first image of a supermassive black hole at the center of our own Milky Way galaxy. This result provides overwhelming evidence that the object is indeed a black hole, and provides valuable clues about the work of such giants that are believed to be at the center of most galaxies. The image was made by a global research group called the Event Horizon Telescope (EHT) Collaboration using observations from a global network of radio telescopes.

The image is a long-awaited view of a massive object that is at the heart of our galaxy. Previously, scientists have seen stars orbiting something invisible, compact and very massive in the center of the Milky Way. This strongly suggests that this object – known as Sagittarius A * (Sgr A *, pronounced “saj-ai-zor”) – is a black hole, and today’s image is the first direct visual proof of this.

Although we cannot see the black hole itself because it is completely dark, the luminous gas around it shows a noticeable sign: a dark central area (called a shadow) surrounded by a bright annular structure. The new species captures light, tilted by the powerful gravity of a black hole that is four million times more massive than our Sun.

“We were stunned by how well the size of the ring matched the predictions of Einstein’s general theory of relativity,” said EHT scientist Jeffrey Bauer of the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei. “These unprecedented observations have greatly improved our understanding of what is happening at the heart of our galaxy, and offer a new insight into how these giant black holes interact with the environment.” The EHT team’s results are published today in a special issue of The Astrophysical Journal Letters.

Since the black hole is about 27,000 light-years from Earth, it seems to us that it is about the same size in the sky as a donut on the moon. To detect it, the team created a powerful EHT that connected eight existing radio observatories around the planet to form a single “Earth-sized” virtual telescope. [1]. EHT observed Sgr A * for several nights in 2017, collecting data for hours on end, much like using long exposure on camera.

In addition to other facilities, the EHT network of radio observatories includes the Atacama Large Millimeter / Submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile, owned and collaborated with ESO on behalf of its European member states. . Europe is also contributing to EHT observations with other radio observatories – the 30-meter IRAM telescope in Spain and, since 2018, the Northern Extended Millimeter Mass (NOEMA) in France – as well as supercomputers to combine EHT data housed at the Institute of Radio Astronomy. Max Planck in Germany. Moreover, Europe has contributed to the EHT consortium project through grants from the European Research Council and the Max Planck Society in Germany.

“It is very interesting for ESO to play such an important role in unraveling the secrets of black holes, and Sgr A *, in particular, for so many years,” commented ESO CEO Xavier Barcons. “ESO has not only contributed to the observation of EHT through the ALMA and APEX facilities, but has also allowed some of its previous breakthrough observations of the galactic center to be carried out with other observatories in Chile.” [2]

The achievement of EHT follows the release of a collaboration in 2019 on the first image of a black hole called M87 *, located at the center of the more distant galaxy Messier 87.

The two black holes look remarkably similar, although the black hole in our galaxy is more than a thousand times smaller and less massive than M87 * [3]. “We have two completely different types of galaxies and two very different masses of black holes, but near the edges of these black holes they look surprisingly similar,” said Sera Markov, co-chair of the EHT Scientific Council and professor of theoretical astrophysics. at the University of Amsterdam, the Netherlands. “It tells us that the General Theory of Relativity governs these objects closely, and any differences we see below must be due to differences in the material surrounding the black holes.”

This achievement was much more difficult than for the M87 *, although the Sgr A * is much closer to us. EHT scientist Chi-Kwan (“CK”) Chan of the Steward Observatory and the Department of Astronomy and the Institute of Data Science of the University of Arizona, USA, explains: “Gas in the vicinity of black holes moves at the same speed – – almost as fast as light – around Sgr A * and M87 *, but if the gas takes days to weeks to process a larger M87 *, in a much smaller Sgr A * it completes its orbit in minutes, meaning the brightness and pattern of the gas around Sgr A * changed quickly when watched by the EHT Collaboration – something like trying to take a clear picture of a puppy quickly chasing its tail. “

The researchers had to develop new sophisticated devices that took into account the movement of gas around Sgr A *. Although the M87 * was a lighter and more stable target, almost all the images looked the same, for the Sgr A * it was not. The image of the black hole Sgr A * is the average value of the various images obtained by the team, and finally, for the first time, a giant is hiding in the center of our galaxy.

These efforts have been made possible by the ingenuity of more than 300 researchers from 80 institutes around the world who together make up the EHT Collaboration. In addition to developing sophisticated tools to overcome Sgr A * visualization challenges, the team worked hard for five years, using supercomputers to combine and analyze their data, creating an unprecedented library of simulated black holes for comparison.

Scientists are particularly excited to finally get images of two black holes of very different sizes, making it possible to understand how they compare and contrast. They also began using new data to test theories and models of how gas behaves around supermassive black holes. This process is not yet fully understood, but it is believed that it plays a key role in the formation and evolution of galaxies.

“We can now study the differences between these two supermassive black holes to gain new valuable clues as to how this important process works,” said EHT scientist Keichi Assad of the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei. “We have images for two black holes – one at the big end and the other at the small end of supermassive black holes in the universe – so we can go much further in testing how gravity behaves in these extreme conditions than ever before. “

Progress in EHT continues: a major observation campaign in March 2022 included more telescopes than ever before. The constant expansion of the EHT network and significant technological updates will allow scientists to share even more impressive images as well as films about black holes in the near future.


[1] The individual telescopes that participated in the EHT in April 2017 when the observations were conducted were: the Large Millimeter / Submillimeter Atacama Massif (ALMA), the Atacama Experimental Trace (APEX), the 30-meter IRAM Telescope, the James Clerk Maxwell Telescope. (JCMT), Alfonso Serrano Large Mill Telescope (LMT), Submillimeter Array (SMA), UArizona Submillimeter Telescope (SMT), South Pole Telescope (SPT). Since then, EHT has added to its network the Greenland Telescope (GLT), the North Extended Millimeter Grid (NOEMA) and the UArizona 12-meter telescope at Keith Peak.

ALMA is a partner of the European Southern Observatory (ESO; Europe, representing member countries), the US National Science Foundation (NSF) and the National Institute of Natural Sciences (NINS) of Japan along with the National Research Council (Canada). ), The Ministry of Science and Technology (MOST; Taiwan), the Institute of Astronomy and Astrophysics Academia Sinica (ASIAA; Taiwan) and the Korean Institute of Astronomy and Space Sciences (KASI; Republic of Korea) in collaboration with the Republic of Chile. The ALMA Joint Observatory is managed by ESO, Associated Universities, Inc. / National Radio Astronomical Observatory (AUI / NRAO) and National Astronomical Observatory of Japan (NAOJ). APEX, a collaboration between the Max Planck Institute for Radio Astronomy (Germany), the Onsal Space Observatory (Sweden) and ESO, is managed by ESO. The 30 – meter telescope is controlled by IRAM (partner organization IRAM – MPG [Germany]CNRS [France] and IGN [Spain]). The JCMT is operated by the East Asian Observatory on behalf of the National Astronomical Observatory of Japan; ASIAA; CASI; National Institute of Astronomical Research of Thailand; Center for Astronomical Megascience and Organization in the United Kingdom and Canada. The LMT is run by INAOE and UMass, the SMA is run by the Center for Astrophysics Harvard & Smithsonian and ASIAA and UArizona SMT are managed by the University of Arizona. SPT is run by the University of Chicago with a specialized EHT instrument provided by the University of Arizona.

The Greenland Telescope (GLT) is operated by the ASIAA and the Smithsonian Astrophysical Observatory (SAO). GLT is part of the ALMA-Taiwan project and is partially supported by Academia Sinica (AS) and MOST. NOEMA is controlled by IRAM, and the 12-meter UArizona telescope at Keith Peak is controlled by the University of Arizona.

[2] A strong basis for the interpretation of this new image was provided by previous studies conducted on Sgr A *. Astronomers have known a bright, dense radio source in the center of the Milky Way toward the constellation Sagittarius since the 1970s. Measuring the orbits of several stars very close to our galactic center for 30 years, a team led by Reinhard Hansel (director of the Max Planck Institute for Extraterrestrial Physics in Garching near Munich, Germany) and Andrea M. Gez (professor at the University of California’s Department of Physics and Astronomy) Los Angeles, USA) were able to conclude that the most likely explanation for an object of such mass and density is a supermassive black hole. ESO tools (including a very large telescope and a very large telescope interferometer) and the Keck Observatory, which won the 2020 Nobel Prize in Physics, were used to conduct this study.

[3] Black holes are the only objects known to us, the mass of which scales with size. A black hole, a thousand times smaller than another, is also a thousand times smaller.

Appendix y Astrophysical Journal Letters, “Focus on the first Sgr A * results from the Event Horizon telescope” https://iopscience.iop.org/journal/2041-8205/page/Focus_on_First_Sgr_A_Results

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