Australian scientists are part of an international team that has captured an image of a supermassive black hole at the center of our own galaxy, the Milky Way.
The image of Sagittarius A* – produced by a global team of scientists known as the Event Horizon Telescope (EHT) collaboration – is the first direct visual confirmation of the black hole’s presence, and comes three years after the first image of it. a black hole from a distant galaxy has been captured.
Australian astronomer Professor Fred Watson said capturing the image, given the size of the black hole and its distance, is a remarkable feat of scientific ingenuity.
“Its resemblance to a humble cream donut belies the extraordinary technological achievement it represents,” he said.
“It shows the shadow of a black hole containing 4.1 million times the mass of the Sun at the very core of our Milky Way, clearly defined by an Earth-sized telescope. Amazingly, the predicted radiation ring narrowly escaping from the clutches of the black hole is visible at a magnification equivalent to what would be needed if the donut were located on the Moon.”
To mark the moment, US donut company Krispy Kreme has declared free donuts on Fridays in its US stores.
The Sagittarius A* black hole is about four million times more massive than our Sun, spanning an area nearly as large as Mercury’s orbit.
US astronomer Katie Bouman said the mechanics of the discovery were only made possible by algorithms that combine images from radio telescopes around the world into a “single virtual Earth-sized telescope”.
“27,000 light years away [from Earth]it’s like trying to photograph a single grain of salt in New York, from Los Angeles (4,488 km),” she said.
“You would need a radio telescope as big as the whole Earth to take a picture of something that small. Building a telescope dish that big is of course impossible. So astronomers got creative.”
Harvard University astronomer Sara Issaoun said the image confirms the existence of a Milky Way black hole that until now had only been suspected.
“For decades we have known about a compact object that lies at the heart of our galaxy and is four million times more massive than our Sun,” she told 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* 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.
The first image of Sagittarius A*, the supermassive black hole at the center of the Milky Way galaxy, is made up of an average of the various images captured by the Event Horizon telescope. Credit: EVENT HORIZON TELESCOPE DOCUMENT/EPA DOCUMENT COLLABORATION
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 how gases behave 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 seeing all those hundreds of scientists who still didn’t prove 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.”