At the center of the Milky Way is a massive and mysterious presence that exerts a powerful influence on the stars that surround it and on the imagination of astronomers.
Scientists now have the first ever photograph of the formidable force at the center of our galaxy: Sagittarius A *, a supermassive black hole with the mass of 4 million suns.
The image, unveiled on Thursday, was captured by a network of eight radio observers in six locations around the world. Together they form the practical equivalent of an Earth-sized telescope designed to see some of the most mysterious and baffling objects in the universe.
Taking a picture of a black hole is a singular undertaking, as its distinguishing feature is that nothing within its gravitational reach can escape, including light.
But astronomers can see the ring-shaped boundary known as the event horizon and beyond, the golden, veiled ring of superheated gas and curved light that borders the black hole’s point of no return.
“What’s more beautiful than seeing the black hole at the center of our Milky Way?” She said Katie BoumanCaltech professor of computational imaging and member of the international telescope team.
The results were published today in Astrophysical Journal Letters.
Black holes are the densest objects in the universe. When a giant star explodes in a dramatic finale supernovaits collapse creates a tiny lump of matter so dense that its gravitational pull deforms the fabric of space and time that surrounds it.
scientists long suspected that supermassive black holes are found at the center of every galaxy, including ours. Yet despite their colossal size, they are an elusive presence in the universe, observable only by their influence on the objects around them.
Capturing the image of an object from which no light can escape is the monumental challenge Event Horizon telescope consortium decided to tackle in 2009. The effort involves the collaborative work of over 300 scientists and engineers in 80 institutions around the world.
It took a decade to produce the first photograph of a black hole, the one at the center of the galaxy of Messier 87 (the black hole is also known as M87 *) about 55 million light years away. Its event horizon is nearly 25 billion miles wide, with a mass roughly that of 6.5 billion suns.
Although Sagittarius A * – or Sgr A * for short – is only 27,000 light years from Earth, it has less than 0.1% of the mass of M87 *. Had it not been conveniently placed in our galaxy, it would have been nearly impossible to photograph. Bouman enjoyed being in Los Angeles and taking a picture of a grain of salt in New York.
“It’s a kinder, more cooperative black hole than we hoped for,” he said Ferial Ozel, University of Arizona astronomer and founding member of the telescope consortium. “We love our black hole”.
Indeed, the images provide the strongest evidence to date for Einstein’s theory of general relativity. With Sgr A * in particular, the size and shape of the ring surrounding the event horizon is remarkably consistent with what scientists predicted based on Einstein’s theory.
“They are so different in so many ways, yet the same theory of gravity actually explains” the shape of both images, Bouman said. “And this is a great result. It’s actually very exciting that they look a lot like “.
A popular class model of a black hole offers a useful way to visualize this cosmic phenomenon. Imagine the fabric of space-time as a stretched plastic sheet and the Earth as a tennis ball falling into the center. The ball will create a slight curve in the film, just as our relatively modest-sized planet does with spacetime.
A steel ball, however, will bend the film further. If the ball is heavy enough, the film will say so much that any other object will inevitably roll towards the heavier one. This is what black holes do to time and space.
“Black holes aren’t the big cosmic vacuum cleaners Hollywood likes to portray them with,” Bouman said.
The smaller, less efficient Sgr A * is more likely a better representative of the typical black hole in the universe than the ultra-massive M87 *, Bouman said.
UCLA astronomers Andrea Ghez What awarded the Nobel Prize in 2020 for having discovered Sgr A *. The image produced by the EHT was “remarkably similar” to the supermassive black hole that she and her colleagues had theorized was at the center of this galaxy.
“There is a prediction that you should see this concentration of light around the black hole, just outside the event horizon, and that you can actually see it is remarkable,” Ghez said. “It’s really exciting.”
Photographing a black hole with a single telescope would have required a lens 13 million meters wide, in other words, a telescope the size of the Earth itself.
In place of this logistical impossibility, the Event Horizon Telescope collects data via eight radio observatories in Greenland, Antarctica and six other intermediate locations, synchronized with atomic clocks. As the Earth rotates, observers view their target from a multitude of angles.
Sgr A * ‘s glam shot was distilled from 5 petabytes of data, which equates to 100 million TikToks, EHT member said Vincenzo Pesce of the MIT Haystack Observatory. The published image is an average of multiple images extracted from that data.
No more than two decades ago, “I thought we would never see images like this. It would be too difficult, “he said Daniele Sternan astrophysicist studying black holes at NASA’s Jet Propulsion Laboratory in La Cañada Flintridge.
“It looked better than I expected,” he said. “It matches decades-old theories about what we thought black holes would look like.”
Since this black hole is much smaller, the ring around it appears much more crowded. Gases that take weeks to orbit M87 * can surround Sgr A * in minutes. Given the rapid changes in emissions, it’s possible the telescope will be able to capture moving images of activity around the event horizon over the next few years, Bouman said, potentially in more dimensions.
“What if we could actually map where the gas is in time in three dimensions around the black hole?” Bouman said. “This is something I’m really excited about.”