Astronomers have revealed the first image of the supermassive black hole at the center of our own Milky Way galaxy, using observations from a global network of radio telescopes.
This result provides overwhelming evidence that the object is indeed a black hole and sheds valuable clues about the workings of such giants, which are thought to reside at the center of most galaxies, according to the discoverers, a research team. called the Event Horizon Telescope (EHT) Collaboration.
The image is a long-awaited look at the massive object that sits at the center of our galaxy. Scientists had previously seen stars orbiting something invisible, compact and very massive at the center of the Milky Way. This strongly suggests that this object, known as Sagittarius A (Sgr A), is a black hole, and today’s image provides the first direct visual evidence of this.
Although we can’t see the black hole itself, because it’s completely dark, the glowing gas surrounding it reveals a telltale signature: a dark central region (called a “shadow”) surrounded by a bright ring-like structure. The new view captures light deflected by the powerful gravity of the black hole, which is four million times more massive than our Sun.
Matches Einstein’s predictions
“We were surprised by how well the ring size matched the predictions of Einstein’s Theory of General Relativity”Geoffrey Bower, EHT project scientist, Institute for Astronomy and Astrophysics, Academia Sinica, Taiwan, said in a statement. “These unprecedented observations have greatly improved our understanding of what is happening at the center of our galaxy and offer new insights into how these giant black holes interact with their surroundings.” The EHT team’s results are published in a special edition of The Astrophysical Journal Letters.
Because the black hole is about 27,000 light-years from Earth, it appears to us to be about the same size in the sky as a donut on the Moon. To get an image, the team created the powerful EHT, which joined eight existing radio observatories around the planet to form a single virtual “Earth-sized” telescope. The EHT observed Sgr A over several nights, collecting data for many hours at a time, similar to using a long exposure time on a camera.
The breakthrough follows the EHT collaboration’s release in 2019 of the first image of a black hole, called M87, at the center of the more distant Messier 87 galaxy.
The two black holes look remarkably similar, even though the black hole in our galaxy is more than a thousand times smaller and less massive than M87. “We have two completely different types of galaxies and two very different black hole masses, but near the edge of these black holes they look amazingly similar,” says Sera Markoff, co-chair of the EHT Science Council and professor of theoretical astrophysics. at the University of Amsterdam, the Netherlands. “This tells us that General Relativity rules these objects up close, and any differences we see further out must be due to differences in the material surrounding the black holes.”
The gas orbits it in minutes
This achievement was considerably more difficult than for M87, although Sgr A is much closer to us. EHT scientist Chi-kwan (‘CK’) Chan, from the Steward Observatory and the Department of Astronomy and the Data Science Institute at the University of Arizona, explains:
“Gas in the vicinity of black holes moves at the same speed: almost as fast as light, around Sgr A and M87. But where the gas takes days to weeks to orbit the larger M87, in the much smaller Sgr A, it completes an orbit in mere minutes. This means that the brightness and pattern of the gas around Sgr A was changing rapidly as the EHT Collaboration observed it, a bit like trying to get a clear picture of a puppy quickly chasing its tail.”
The researchers had to develop sophisticated new tools to explain the movement of gas around Sgr A. While M87 was an easier and more stable target, with almost all images looking the same, that was not the case for Sgr A. The Sgr A black hole image is an average of the different images the team extracted, finally revealing the giant lurking at the center of our galaxy for the first time.
The effort was 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 complex tools to overcome the challenges of imaging Sgr A, the team worked rigorously for five years, using supercomputers to combine and analyze their data, while compiling an unprecedented library of simulated black holes to compare with observations.
Scientists are particularly excited to finally have images of two black holes of vastly different sizes, offering an opportunity to understand how they compare and contrast. They have also begun to use the new data to test theories and models about how the gas around supermassive black holes behaves. This process is not yet fully understood, but it is believed to play a key role in the formation and evolution of galaxies.
“Now we can study the differences between these two supermassive black holes to gain valuable new clues about how this important process works.” said EHT scientist Keiichi Asada of the Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan. “We have images of two black holes, one at the big end and one at the small end of supermassive black holes in the Universe, so we can go much further than ever before to test how gravity behaves in these extreme environments.” .
Progress on the EHT continues: a major observing campaign in March 2022 included more telescopes than ever before. The ongoing expansion of the EHT network and major technology upgrades will enable scientists to share even more impressive black hole images and movies in the near future, the finding statement concludes.