Astronomers have finally seen the center of the Milky Way and unveiled a giant black hole, a celestial vortex 26,000 light-years from Earth that should otherwise have remained hidden.
An international team of researchers released a snapshot of the supermassive black hole dubbed Sagittarius A* on Thursday., spied on by the power of eight interconnected radio dishes from around the world, which together can penetrate gas clouds in space. Although black holes are not visible by definition – light cannot travel fast enough to escape their clutches – Sagittarius A* revealed itself as a black shadow surrounded by the bright glow of the gas and debris swirling around its perimeter .
The photo showed a region in space reminiscent of a solar eclipse – a dark circle surrounded by a glow of bright red-orange light. The image was colorized for human eyes to perceive.
Until three years ago, any depiction of a black hole was merely an artistic interpretation or computer model of what the spinning, spacetime-warping phenomenon might look like. This object, seen in the photo at the top of this story, is the real deal, with each pixel representing a Herculean feat: hundreds of scientists from 80 institutions around the world working together to collect, process, and piece together fragments of data .
The breakthrough was also published in the science journal Astrophysical Journal Letters. Speakers from the Event Horizon Telescope, the international collaboration of 300 scientists who worked on the feat, held simultaneous press conferences in at least seven countries to share the news, including the United States at the National Press Club in the country’s capital.
The image of Sagittarius A*, pronounced “Sagittarius A-Star,” is a monumental achievement, the second time scientists have broken the barrier of invisibility to glimpse a black hole. The first photo, revealed in April 2019, showed the black hole at the center of the galaxy Messier 87, which is an easier target to target because of its size, despite being much more distant, some 53 million light-years away. Astronomers say the black hole, labeled M87*, is as big as Earth’s solar system of eight planets.
The second photo is strong endorsement for the scientific community, said Feryal Özel, a professor of astronomy and physics at the University of Arizona.
“Now we know it wasn’t a coincidence — it wasn’t an aspect of the setting that happened to look like the ring we were expecting,” she said at the news event in Washington, DC. “Now we know that what we see in both cases is the heart of the black hole, the point of no return. These two images look similar because they are the result of fundamental gravitational forces.”
Astronomers see the first supermassive black hole as it grows
This graphic shows how much larger the supermassive black hole in galaxy M87 is than Sagittarius A* (which lies at the center of our Milky Way).
Photo credit: National Science Foundation / Keyi “Onyx” Li
Sagittarius A*, or Sgr A* for short, is considerably smaller, at about 27 million miles across, but it’s no tiny thing. Scientists estimate it is 4 million times more massive than the Sun. To make an elusive number even more inscrutable, imagine this: The mass of the Sun is equal to 333,000 Earths.
Its home Milky Way, a spiral galaxy, is fairly flat, but the center slopes downward where the supermassive black hole sits. Around him are stars darting in different directions. But the hole, which pop culture often humanizes as a space monster, is actually quite “gentle,” researchers say, consuming relatively little of its surroundings.
Black holes are among the most elusive things in space. The most common type, called a stellar black hole, is often thought to be the result of a giant star dying in a supernova explosion. The star’s material then collapses on itself, condensing into a relatively small area.
But how supermassive black holes, millions to billions of times more massive than the Sun, form is even more mysterious than typical stellar black holes. Many astrophysicists and cosmologists believe these giants lurk at the center of virtually every galaxy. Recent observations from the Hubble Space Telescope have supported the theory that supermassive black holes begin in the dusty cores of starburst galaxies where new stars are rapidly forming, but scientists are still working on the problem.
Black holes don’t have surfaces like a planet or star. Instead, they have a boundary called the “event horizon.” It’s a point of no return. If anything gets too close, it will fall in without escaping the gravitational pull of the hole.
Ahead of the groundbreaking May 12 image, the Event Horizon Telescope team released the first photo of a black hole in the galaxy Messier 87 in April 2019.
Credit: Chip Somodevilla/Getty Images
If M87* Proof that black holes weren’t science fiction, Sgr A* is the testimony of decades of increasing observational science. Before the first photo of a black hole, scientists inferred the presence of a hole in space by discovering its effects on nearby stars and gas. Albert Einstein, whose theory of general relativity predicted black holes over a century ago, and Stephen Hawking, a cosmologist who devoted much of his career to mathematically proving their existence, are among the many figures who paved the way for Thursday’s unveiling .
If M87* proved that black holes weren’t science fiction, Sgr A* is the testimony of decades of increasing observational science.
Sgr A* is exciting to scientists because it is ordinary, said Michael Johnson of the Harvard Smithsonian Center for Astrophysics. The central supermassive black hole is representative of many others in the universe and allows experts to learn more about these mysterious space objects.
Despite their visual similarities — a flaming donut versus another flaming donut — the two black holes couldn’t be more different, scientists said. M87* accumulates matter much faster, but the Milky Way’s central black hole is changing appearance faster: it takes only a few minutes for gas to fully orbit it, while an orbit around its ancestor takes about two weeks.
In addition, the first black hole photographed emits a huge beam of radiation that extends to the edge of its galaxy, while Sgr A* does not.
To collect the massive amount of data needed to process the new image, the Event Horizon Telescope used a technique called very-long-baseline interferometry, which synchronizes observatories around the world and uses the Earth’s rotation to create a planet-sized virtual telescope form . Taken together, the instruments were able to see the sky with a view equivalent to the organization required to read a newspaper in New York from Paris.
At the time of the black hole’s announcement in 2019, staff at the Event Horizon Telescope said they had attempted to create an image of this supermassive black hole as well, but the team had been unable to get a clear picture. As one of the best-studied supermassive black holes in the universe, this has been a disappointment to many astrophysicists who have longed to look at our galaxy’s own navel.
“For me personally, I got to know it 20 years ago and have loved it ever since and tried to understand it,” Özel said on Thursday.
This time, scientists added the South Pole Telescope, which was not used in the M87* photo, to the virtual telescope array to improve the resolution of their images. The researchers collected five petabytes worth of data, about 2.5 trillion pages of printed text, to capture even a glimpse of this black hole, said Dom Pesce, a member of the telescope team.
Put another way, that’s the equivalent amount of data in about 100 million TikTok videos, said Vincent Fish, a research scientist at MIT’s Haystack Observatory. That’s far too much to stream over the internet, so scientists had to ship hundreds of hard drives to two centers in western Massachusetts and Bonn, Germany, where supercomputers could process the raw data.
Photo credit: Daniel Michalik / National Science Foundation
Granted, the Sgr A* photo is blurry. Johnson compared the blur to looking through frosted glass. Radio waves, which contain important image details, are scattered, making the hole’s sharp outline look more like a jelly ring. To fix that, the telescopes either need to be farther apart or reach higher frequencies, he said.
“We don’t think the black hole is actually a blurred image in the sky,” Johnson said. “We’re at our breaking point right now.”
“We don’t think the black hole is actually a blurred image in the sky.”
With funding from the National Science Foundation and other groups, scientists plan to improve their technology to dramatically sharpen the image.
Another next step in the collaboration is trying to turn these still images into video so scientists can watch gas fall toward black hole event horizons. That project could be completed sometime after 2024, they said.
But in case anyone out there is stunned by another flaming donut, Katie Bouman, an assistant professor of astronomy at Caltech, recalled just how much data is packed into the image.
“This image is actually one of the sharpest images you’ve ever seen,” she said.