An image of the supermassive black hole has been captured at the heart of the Milky Way, giving the first direct glimpse of the “gentle giant” at the center of our galaxy.
The black hole itself, known as Sagittarius A*, cannot be seen because no light or matter can escape its gravitational grip. But its shadow is traced by a glowing, mysterious ring of light and matter spinning over the edge of the abyss at nearly the speed of light.
The image was taken by the Event Horizon Telescope (EHT), a network of eight radio telescopes stretching from Antarctica to Spain and Chile, which produced The first image of a black hole in a galaxy called Messier 87 in 2019.
“The Milky Way’s black hole was our main target, it’s our closest supermassive black hole and that’s why we set out to do this thing in the first place,” said Professor Cera Markov, an astrophysicist at the University of Amsterdam and co-chair of the EHT Science Council. It’s been 100 years of researching these things and so, scientifically speaking, it’s a huge deal.”
The image provides compelling evidence for the presence of a black hole at the center of the Milky Way, which has been a working assumption of mainstream astronomy. A minority of scientists have continued to speculate about the possibility of other exotic objects, such as bosons or clumps of dark matter.
“I’m personally happy with the fact that he’s studying the fact that there is definitely a black hole at the center of our galaxy,” said Dr. Zeri Younesi, an EHT member based at University College London.
To the untrained eye, the last image may look almost similar to That black hole, M87*but the two objects are very different, according to the EHT team.
Sagittarius A* consumes very little material, in contrast to the typical depiction of black holes as violent, predatory beasts of the universe. “If SgrA* was a person, it would only consume one grain of rice every million years,” said Michael Johnson of the Harvard-Smithsonian Center for Astrophysics.
By contrast, M87* is one of the largest black holes in the universe and features massive, powerful jets that shoot light and matter from their poles into intergalactic space.
“Sgr A* gives us a look at the state of the most common black holes: calm and quiet,” Johnson said. “[It] Sexy because it’s popular.”
Recent observations also show that the black hole’s rotation angle is not precisely in line with the plane of the galaxy, but is a far cry from about 30 degrees, and hints at amazing magnetic activity similar to that seen in the Sun’s atmosphere. Beyond science, astronomers have acknowledged an emotional connection to seeing the mysterious object our galaxy orbits around.
“It’s another cake, but it’s our donut,” Yonsei said.
Despite being astronomically local to 26,000 light-years away, observing SgrA* has turned out to be more challenging than expected. The team spent five years analyzing data obtained during an occasional clear sky across several continents in April 2017.
Sagittarius A* Relatively small, which means the dust and gas are in its increasing disc orbit in a matter of minutes rather than weeks, creating a target moving from one observation to the next. Markov compared the observations to trying to photograph a puppy chasing its tail using a camera with a slow shutter speed. The scientists also had to look across the galactic plane and filter out interfering stars and dust clouds from their images. A combination of these factors – and possibly some extreme black hole phenomena – explain the bright spots in the image.
“We didn’t expect how evasive and evasive it would be,” Yonsei said. “It was really a tough picture. It’s hard to overstate it.”
The EHT captures radiation from particles within the accretion disk that are heated to billions of degrees as they orbit the black hole before sinking into the central vortex. The speckled corona in the image shows the light being bent by the strong gravitational pull of the black hole, which is four million times more massive than our sun.
Ultimately, scientists hope that observing a group of black holes — somewhat inert like our giants and turbulent like M87* — will help answer a chicken-and-egg question about the evolution of galaxies.
It is an open question in the formation and evolution of galaxies. “We don’t know which came first, the galaxy or the black hole,” said Professor Carol Mondel, an astrophysicist at the University of Bath, who is not part of the EHT collaboration.
“From a technology perspective, it’s amazing that we can do this,” she said of the latest images.
The EHT team’s findings were published Thursday in a special issue of Astrophysical Journal Letters.
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