This is the first direct observation confirming 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 black hole’s shadow surrounded by a bright ring, which is distorted by the black hole’s gravity. Astronomers have said 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 tight orbits thanks to its immense gravity,” said Michael Johnson, astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, said in a statement.
“With the image (Event Horizon Telescope or EHT), we have zoomed a thousand times closer than these orbits, where gravity becomes a million times stronger. At this close distance, the black hole is accelerating matter at a speed close to of the speed of light and bends the trajectories of photons in the warped spacetime.”
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 appear to be about the size of a donut sitting on the moon.
“We were amazed at how well the size of the ring matched the predictions of Einstein’s theory of general relativity,” said EHT project scientist Geoffrey Bower of the Institute of Astronomy and Science. Astrophysics, Academia Sinica, Taipei, in a statement.
“These unprecedented observations have dramatically 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 environment.”
In search of 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 at the center of the galaxy.
“We now see that the black hole is swallowing nearby gas and light, dragging them down a bottomless pit,” said 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 eat.”
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 called the “event horizon”, the point at which no light can escape from a black hole. This global network of telescopes essentially forms a single virtual “Earth-size” telescope when all eight are linked and observe in tandem.
Although 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 black hole masses, but near the edge of these black holes they look amazingly similar,” said Sera Markoff, co-chair of the EHT Science Council and professor of science. theoretical astrophysics at the University of Amsterdam, in a statement.
“This tells us that (Einstein’s theory of) general relativity governs these objects up close, and any differences we see farther out must be due to differences in the material that surrounds the black holes.”
Capturing an impossible image
Although the Milky Way’s black hole is closer to Earth, it was much harder to imagine.
“Gas near black holes moves 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 from the Department of Astronomy and the Data Science Institute at the University of Arizona, said in a statement.
“But where the gas takes days or even weeks to orbit the larger M87*, in the much smaller Sgr A* it completes an orbit in minutes. This means that the brightness and pattern of the gas around of Sgr A* changed rapidly as the EHT collaboration watched — much like trying to take a clear picture of a puppy quickly chasing its tail.”
The worldwide network of astronomers had to develop new tools to enable the rapid movement of gas around Sagittarius A*. The resulting image is an average of different takes by the team. Taking the image of Sagittarius A* was like capturing a photo of a grain of salt in New York using a camera in Los Angeles, according to researchers at the California Institute of Technology.
“This Event Horizon Telescope image required more than just taking pictures from telescopes atop high mountains. It is the product of both technically challenging telescope observations and innovative computational algorithms,” said Katherine Bouman, Rosenberg researcher and assistant professor of computer science and mathematical sciences. , electrical engineering and astronomy at Caltech, said at a press conference.
Every telescope has been pushed to its limit, called the diffraction limit, or the maximum fine features it can see.
“And that’s basically the level we see here,” Johnson said at the press conference. “It’s blurry because to get a sharper picture we have to move our telescopes further away or go into higher frequencies.”
on the horizon
Having 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 at the center of most galaxies, acting as an engine that powers them.
Meanwhile, the EHT team is working to expand the telescope array and make upgrades that could lead to even more stunning images, and even movies, of black holes in the future.
Capturing a moving black hole can show how it changes over time and what gas does as it swirls around a black hole. Bouman and EHT fellow Antonio Fuentes, who will join Caltech as a postdoctoral researcher in October, are developing methods that will allow them to stitch together images of the black hole to reflect this motion.
This “first direct image of the gentle giant at the center of our galaxy” is just the start, said Feryal Özel, EHT Science Council member and professor of astronomy and physics and associate dean for research. at the University of Arizona, during the press conference.
“This image is a testament to what we can accomplish, when as a global research community, we bring together our brightest minds to make possible what seems impossible,” said National Science Foundation Director Sethuraman Panchanathan. in a press release. “Language, continents, and even the galaxy cannot stand in the way of what humanity can achieve when we come together for the greater good of all.”