(ORDO NEWS) — In simultaneous press conferences around the world, including a press conference hosted by the National Science Foundation in Washington, astronomers have unveiled the first image of a supermassive black hole at the center of our own Milky Way galaxy.
This result provides incontrovertible evidence that the object is indeed a black hole and provides valuable insight into the workings of such giants, which are thought to be at the center of most galaxies.
The image was taken by a research group called the Event Horizon Telescope (EHT) Collaboration using observations from a worldwide network of radio telescopes.
This image is a long-awaited glimpse of a massive object located at the very center of our galaxy. Scientists have previously seen stars revolving around something invisible, compact and massive at the center of the Milky Way.
This suggested 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.
We can’t see the black hole itself because it’s completely dark, but the luminous gas around it makes itself felt: the dark central region (the so-called “shadow”) is surrounded by a bright ring-like structure.
The new image captures light warped by the powerful gravity of a black hole 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 project scientist Geoffrey Bower of the Academia Sinica Institute of Astronomy and Astrophysics, Taipei.
“These unprecedented observations have greatly improved our understanding of what is happening at the very center of our galaxy and provide new insight into how these giant black holes interact with their surroundings.” The results of the EHT team’s work are published today in a special issue of The Astrophysical Journal Letters.
To image it, the team created a powerful EHT system that combined eight existing radio observatories around the planet into a single “Earth-sized” virtual telescope. The EHT observed Sgr A* over several nights, collecting data for many hours at a time, similar to using a long exposure in a camera.
As with a powerful camera, imaging Sgr A* required the support of the most sensitive instruments in radio astronomy.
This sensitivity is provided by 1.3mm Band 6 receivers on the Atakama Large Millimeter/Submillimeter Array (ALMA) developed by the Central Development Laboratory (CDL) of the US National Science Foundation’s National Radio Astronomy Observatory (NRAO).
“We are very proud that the CDL has provided some important technology to support this amazing EHT collaborative discovery,” said Bert Hawkins, director of the CDL, who explained the role of Band 6 and the CDL in conducting the study and delivering the results.
“Our team contributed by installing a custom-made atomic clock on ALMA and reprogramming the ALMA correlator to make the telescope a phased array. This effectively turned the telescope into a single antenna with an effective diameter of 85 meters – the largest component on the EHT.
In addition, the mixers, underlying receivers at ALMA, the Submillimeter Telescope (SMT) in Arizona, the Large Millimeter Telescope (LMT) in Mexico, and the South Pole Telescope (SPT) in Antarctica,
The breakthrough came after the EHT collaboration published the first image of a black hole, named M87*, at the center of the more distant galaxy Messier 87 in 2019.
The two black holes look surprisingly similar, despite the fact that our galaxy’s black hole is more than 1,000 times smaller and less massive than M87*.
“We have two very different types of galaxies and two very different black hole masses, but near the edge of these black holes they look surprisingly similar,” says Sera Markoff, co-chair of the EHT Science Council and professor of theoretical astrophysics at the University of Amsterdam (Netherlands).
“This tells us that general relativity governs these objects up close, and any differences we see farther away must be due to differences in the material that surrounds black holes.”
This achievement was significantly more difficult than for M87*, despite the fact that Sgr A* is much closer to us.
EHT scientist Chi-Kwan (“CK”) Chan of the Steward Observatory, Department of Astronomy, University of Arizona, USA, explains: “Gas in the vicinity of black holes moves at the same speed – almost like light – around Sgr A* and M87*.
But there, where it takes days to weeks for the gas to go around the large M87*, in the much smaller Sgr A* it orbits in a matter of minutes, meaning that the brightness and structure of the gas around Sgr A* changed rapidly during the EHT collaboration’s observations approximately like trying to get a clear shot of a puppy chasing its tail.”
The researchers had to develop sophisticated new instruments that took into account the movement of gas around Sgr A*.
While the M87* was a lighter, more stable target and almost all images looked the same, the Sgr A* was different. The image of the black hole Sgr A* is the average of all the images taken by the team, allowing for the first time to see the giant lurking at the center of our galaxy.
This work was made possible thanks to the ingenuity of more than 300 researchers from 80 institutions around the world that make up the EHT collaboration.
In addition to developing sophisticated tools to overcome the challenges of visualizing Sgr A*, the team worked for five years using supercomputers to combine and analyze data, while building an unprecedented library of simulated black holes for comparison with observations.
“This work clearly demonstrates the critical importance of using radio, millimeter and submillimeter frequencies to understand the most extreme environments in the universe,” said Tony Remijian, director of the ALMA North American Science Center (NAASC) at NRAO.
Using these frequency bands is the only way to reveal the unique conditions surrounding a black hole that are completely hidden at other frequencies.”
The addition of ALMA was also critical to the observations, as it provided the necessary sensitivity to make these observations unambiguously. world – with ALMA as the anchor for all of these objects – has provided the sensitivity and resolution needed to make these kinds of discoveries.And this is just the beginning.
Scientists are particularly excited to finally be able to image two black holes of vastly different sizes, making it possible to understand how they compare and contrast.
They also began to use the new data to test theories and models of the behavior of the gas around supermassive black holes. 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 insights into how this important process works,” said EHT scientist Keiichi Asada from the Academia Sinica Institute of Astronomy and Astrophysics in Taipei.
“We have images of two black holes – one at the large end and one at the small end of supermassive black holes in the universe – so we can go much further than ever before in studying the behavior of gravity under these extreme conditions.”
Progress continues at the EHT, with a major observing campaign in March 2022 including more telescopes than ever before. The continuous expansion of the EHT network and significant technological improvements will allow scientists to share even more impressive images and films about black holes in the near future.
In 2021, NSF and the ALMA Council approved a multi-million dollar upgrade to the observatory’s Band 6 receivers as part of ALMA’s North American Development Program.
The upgrade will increase the quantity and quality of scientific measurements in the 1.4 mm to 1.1 mm wavelength range, giving research projects like the EHT project better sensitivity than ever and ultimately more accurate and efficient scientific results.
In addition, the NRAO Next Generation Very Large Array (ngVLA) project received positive support as part of the 10-year Astro2020 review. While at an early stage of planning and development, ngVLA will achieve priority goals in astronomy and astrophysics and become the best machine for finding black holes.
“These new results from the EHT excite us both because they show how far astronomy has come, and because they confirm that there is still much that we haven’t seen and haven’t been able to observe and study,” said Dr. r Tony Beasley, director of the NRAO.
“The antennas and instruments we design and develop at NRAO make this progress possible, and we look forward to continuing to lead advances in radio astronomy that will enable us to detect black holes and other phenomena lurking in the corners of the galaxy and the universe.”
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