This is the first direct observation to confirm the presence of the black hole known as Sagittarius A * as the beating heart of the Milky Way.
Black holes do not emit light, but the image shows the shadow of the black hole surrounded by a bright ring, which is light bent by the gravity of the black hole. Astronomers say the black hole is 4 million times more massive than our sun.
“For decades, astronomers have wondered what lies at the heart of our galaxy, pulling stars into narrow orbits through their enormous gravity,” said Michael Johnson, an astrophysicist at the Center for Astrophysics. Harvard & Smithsonian, said in a statement.
“With the image (Event Horizon Telescope or EHT), we have come a thousand times closer to these orbits, where gravity is growing a million times stronger. At this close distance, the black hole accelerates matter to the speed of light and bends the paths of photons in distorted (space-time).
The black hole is about 27,000 light-years from Earth. Our solar system is located in one of the spiral arms of the Milky Way galaxy, which is why we are so far from the galactic center. If we could see this in our night sky, the black hole would look the same size as a donut sitting on the moon.
“We were stunned by how well the ring size matched Einstein’s predictions of general 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 very center of our galaxy and offer new insights into how these giant black holes interact with their surroundings.
The results of this revolutionary discovery were published Thursday in a special issue of The Astrophysical Journal Letters.
Search for the black hole
It took astronomers five years to capture and confirm this image and discovery. Previously, scientists observed stars orbiting an invisible massive object in the galactic center.
The 2020 Nobel Prize in Physics was awarded to scientists Roger Penrose, Reinhard Hansel and Andrea Gez for their discoveries of black holes, including evidence shared by Gez and Hansel about the mass of the object at the center of the Milky Way.
“Now we see that the black hole absorbs nearby gas and light, pulling them into a bottomless pit,” Ramesh Narayan, theoretical astrophysicist at the Center for Astrophysics. Harvard & Smithsonian, said in a statement. “This image confirms decades of theoretical work to understand how black holes feed.
The discovery was made possible by more than 300 researchers from 80 institutions working with a network of eight different radio telescopes around the world that make up the Event Horizon Telescope.
The telescope is named after the “event horizon”, the point at which no light can escape a black hole. This global telescope network essentially forms a single “Earth-sized” virtual telescope, when all eight are connected and observed in tandem.
This is the second image ever taken on a black hole, the first being the EHT’s achievement to depict M87 * in the heart of the distant galaxy Messier 87, 55 million light-years away in 2019.
While the two images look similar, Sagittarius A * is more than 1,000 times smaller than M87 *.
“We have two completely different types of galaxies and two very different masses of black holes, but near the edge of these black holes they look incredibly similar,” said Sera Markov, co-chair of the EHT Scientific Council and professor of theoretical astrophysics at the University of Amsterdam. in a statement.
“This tells us that (Einstein’s theory) The general theory of relativity governs these objects closely, and all the differences we see further must be due to differences in the material that surrounds black holes.”
Capture an impossible image
Although the black hole of the Milky Way is closer to Earth, it was much more difficult to depict.
“Gas near black holes travels at the same speed – almost as fast as light – around Sgr A * and M87 *,” said EHT scientist Chi-kwan Chan of the Steward Observatory and the Department of Astronomy and the Institute of Data Science. The University of Arizona said in a statement.
“But when the gas takes days to weeks to orbit the larger M87 *, in the much smaller Sgr A * it completes its orbit in just minutes. This means that the brightness and pattern of the gas around the Sgr A * changed quickly as I watched the EHT Collaboration – a bit like trying to take a clear picture of a puppy quickly chasing its tail. “
The global network of astronomers had to develop new tools to allow the rapid movement of gas around Sagittarius A *. The resulting image is an average of different made by the team. Taking a picture of Sagittarius A * was like taking a picture of a grain of salt in New York with a camera in Los Angeles, according to researchers at the California Institute of Technology.
“This image from the Event Horizon Telescope required more than just taking a picture of telescopes on high mountain peaks. It is the product of both technically challenging telescope observations and innovative computational algorithms, “said Katherine Bohmann, a Rosenberg scientist and assistant professor of computer and mathematical science, electrical engineering and astronomy at Caltech, at a news conference.
Bowman is also working on the M87 * image, shared in 2019. Despite the fact that the Sagittarius A * image may look blurry, “it’s one of the sharpest images ever made,” Bowman said.
Each telescope was pushed to its limit, which is called the diffraction limit or the finest characteristics it can see.
“And that’s basically the level we see here,” Johnson told a news conference. “It’s blurry, because to make a sharper image, we have to move our telescopes farther or go to higher frequencies.”
On the horizon
The presence of images of two very different black holes will allow astronomers to determine their similarities and differences and better understand how gas behaves around supermassive black holes, which could contribute to the formation and evolution of galaxies. Black holes are thought to exist in the center of most galaxies, acting as the engine that powers them.
Meanwhile, the EHT team is working to expand the telescope network and make upgrades that could lead to even more stunning images and even black hole movies in the future.
Capturing a black hole in motion can show how it changes over time and what the gas does as it rotates around a black hole. Bouman and EHT member Antonio Fuentes, who will join Caltech as a postdoctoral fellow in October, are developing methods that will allow them to put together images of the black hole to reflect this movement.
This “first direct image of the gentle giant at the center of our galaxy” is just the beginning, said Ferial Ozel, a member of EHT’s scientific council and professor of astronomy and physics and vice dean for research at the University of Arizona, at a news conference. .
“This image is proof of what we can achieve when, as a global research community, we unite our brightest minds to make the seemingly impossible possible,” said Seturaman Pancanathan, director of the National Science Foundation. “Language, continents and even galaxies cannot stand in the way of what humanity can achieve when we come together for the greater good of all.”
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