Paris: An international team of astronomers on Thursday unveiled the first image of a supermassive black hole at the center of our own galaxy, the Milky Way – a cosmic body known as Sagittarius A*.
The image – produced by a global team of scientists known as the Event Horizon Telescope (EHT) collaboration – is the first direct visual confirmation of the presence of this unseen object, and comes three years after the first-ever image of a black hole of a distant galaxy.
“For decades, we have known about a compact object that sits at the heart of our galaxy and is four million times more massive than our Sun,” Harvard University astronomer Sara Issaoun said during an interview. a press conference in Garching, Germany, held simultaneously with other media. events around the world.
“Today, right now, we have direct evidence that this object is a black hole.”
Black holes are regions of space where the pull of gravity is so intense that nothing can escape, including light.
The image therefore does not represent the black hole itself, because it is completely dark, but the incandescent gas which encircles the phenomenon in a luminous ring of bent light.
Seen from Earth, it appears the same size as a donut on the surface of the Moon, Issaoun explained.
“These unprecedented observations have dramatically improved our understanding of what is happening at the very center of our galaxy,” EHT project scientist Geoffrey Bower of Taiwan’s Academia Sinica said in a statement.
The research results are published in The Astrophysical Journal Letters.
Sagittarius A* – abbreviated as Sgr A*, and pronounced “sadge-ay-star” – owes its name to its detection in the direction of the constellation of Sagittarius.
Located 27,000 light-years from Earth, its existence has been speculated since 1974, with the detection of an unusual radio source at the center of the galaxy.
In the 1990s, astronomers mapped the orbits of the brightest stars near the center of the Milky Way, confirming the presence of a supermassive compact object there – work that led to the 2020 Nobel Prize in Physics.
Although the presence of a black hole was considered the only plausible explanation, the new image provides the first direct visual evidence.
Capturing images of such a distant object required linking eight giant radio observatories across the planet to form a single virtual “Earth-sized” telescope called the EHT.
“The EHT can see three million times sharper than the human eye,” German scientist Thomas Krichbaum of the Max Planck Institute for Radio Astronomy told reporters.
“So when you’re sitting in a beer garden in Munich, for example, you could see the bubbles in a glass of beer in New York.”
The EHT looked at Sgr A* over multiple nights for several hours at a stretch – an idea similar to long exposure photography and the same process used to produce the first image of a black hole, published in 2019.
This black hole is called M87* because it is in the galaxy Messier 87.
Einstein would be “ecstatic”
The two black holes have striking similarities, despite the fact that Sgr A* is 2,000 times smaller than M87*.
“Close to the edge of these black holes, they look amazingly similar,” said Sera Markoff, co-chair of the EHT Scientific Council and professor at the University of Amsterdam.
Both behaved as predicted by Einstein’s 1915 theory of general relativity, which holds that the force of gravity results from the curvature of space and time, and that cosmic objects alter this geometry.
Despite Sgr A* being much closer to us, his imagery presented unique challenges.
The gas near the two black holes is moving at the same speed, close to the speed of light. But while the larger M87* took days and weeks to orbit, it completed Sgr A* laps in just minutes.
The brightness and pattern of the gas around Sgr A* changed rapidly as the team observed it, “much like trying to take a clear picture of a puppy rapidly chasing its tail,” said EHT scientist Chi -kwan Chan from the University of Arizona. .
Researchers had to develop complex new tools to account for moving targets.
The resulting image – the work of more than 300 researchers in 80 countries over a five-year period – is an average of several images that revealed the invisible monster lurking at the center of the galaxy.
“The fact that we’re able to make an image out of it, something that should be invisible… I think that’s really exciting,” Katie Bouman, a Caltech professor who played a role, told AFP. key role in creating the image. .
Scientists are now eager to compare the two black holes to test theories about the behavior of gases around them – a poorly understood phenomenon believed to play a role in the formation of new stars and galaxies.
Probing black holes — specifically their infinitely small, dense centers called singularities, where Einstein’s equations break down — could help physicists deepen their understanding of gravity and develop more advanced theory.
“And Einstein? Would he smile when he saw all those hundreds of scientists who still hadn’t proved him wrong? said Anton Zensus of the Max Planck Institute.
“I rather think that he would be delighted to see all the experimental possibilities that we have in this field today.”