Astronomers look at the core of the Milky Way to get the first image of the ‘supermassive black hole next door’

For ninety years, astronomers have known that something powerful lurks in the crowded heart of our galaxy, the Milky Way. Now, at last, they have seen it.

On Thursday, an international team of researchers reported that they have succeeded in their attempt to pierce the dusty veil that hides the galactic center from view and have produced the first direct image of the giant black hole that resides there.

Their achievement, a scientific tour de force involving coordinated observations made at multiple locations followed by years of data processing and analysis, uncovers the most intriguing and exotic object in humanity’s corner of the universe. And it sets the stage for years of follow-up measurements to reveal the detailed features of a black hole that is about four million times more massive than our sun along with the complex ways it interacts with and shapes its immediate environment.

“It’s the supermassive black hole next door,” said Avery Broderick, a researcher at the University of Waterloo and the Perimeter Institutes for Theoretical Physics.

Dr. Broderick is a long-time member of the Event Horizon Telescope, a project that harnesses radio observatories around the world for the sole purpose of revealing what a black hole is really like.

The goal may seem like a contradiction in terms. A black hole, by definition, is an object so dense that not even light can escape its powerful gravitational pull. But black holes are also drawn in hot ionized gas ripped from nearby stars or clouds of interstellar material. The glowing gas creates a backdrop against which the silhouette of the black hole’s dark edge, its event horizon, can be seen.

It is this kind of image that Dr. Broderick and his colleagues have now created: a glowing fizzy donut with a dark void in the center.

The shape of the image “is the telltale sign of the black hole,” Feryal Ozel, a project member and an astronomer at the University of Arizona, said during a news conference in Washington, DC, following the release of the team’s results.

The images mark the second time the project has made astronomical history.

In 2019, the collaboration garnered global attention when it produced the first direct image of a black hole. On that occasion, the target was a much more distant object: a gigantic black hole that is 6.5 billion times the mass of the sun located in the galaxy M87. That image proved achievable simply because the black hole is so big, close to the theoretical limit of how big a black hole can get. Even a beam of light takes a whole week to go around its impressive circumference.

In contrast, the black hole at the center of the Milky Way is 1,500 times smaller but, by cosmic coincidence, about 2,000 times closer. That means it’s about the same size in the sky from Earth’s point of view, making it equally accessible to the Event Horizon Telescope. But while the black hole inside M87 can be seen from 55 million light-years of empty intergalactic space, the Milky Way’s black hole is shrouded behind layers of dust in the densest part of our own galaxy, about 26,000 miles away. light years away. The contrast is akin to looking at a large building across an open lake and seeing it more easily than a birdhouse hidden in the nearby forest.

An additional challenge is that because the Milky Way’s black hole is smaller, it changes on timescales that make it challenging to observe. The electrified gas swirling around the black hole can suddenly explode when magnetic field lines break and reconnect, releasing large amounts of energy and causing minute-to-minute variations that confound the imaging process.

The black hole “bubbled and gurgled as we looked at it,” Dr Ozel said.

Only after overcoming the Everest twins of dimming and variability was the team ready to publish their image of the black hole, five years after the first observations were made, Dr Broderick said. The results were published simultaneously in a series of six scientific papers in the Astrophysical Journal.

At first glance, the two images look remarkably similar in a side-by-side comparison. Team members said this offers confidence that what they are seeing is physical reality and not an artifact of the imaging process. The shapes and dimensions of each black hole are the product of the same physical rules, detailed in the mathematics of Einstein’s General Theory of Relativity.

“We now know that what we see in both cases is the heart of the black hole, the point of no return,” said Dr. Ozel.

The James Webb Space Telescope captures the sharpest views of the universe in an “extraordinary milestone for humanity”

In each case, the resulting image is not an optical photograph but a map of the radio energy emitted by the ionized gas around the black holes. The images are produced by combining observations from multiple radio telescopes located around the world, including at the South Pole. Through a process known as interferometry, astronomers combined data from each of the observatories to build an image as sharp as if it had been produced by a single radio dish nearly as big as Earth.

The Milky Way photo marks a highlight for the Event Horizon Telescope, as well as a much longer odyssey for astronomers to understand the source of energy at the center of our galaxy.

That odyssey began in the early 1930s when Karl Jansky, an American physicist working for Bell Telephone Laboratories, was tasked with discovering the natural sources of radio interference. He discovered one of those sources tracked with the sky. After ruling out the sun, he concluded that the source was astronomical, located in the constellation of Sagittarius, which coincides with the center of the Milky Way.

Radio waves can penetrate dust clouds that block the view of the galaxy’s center. As the technology matured, radio astronomers realized that there were multiple sources of energy in the galaxy, including a particularly strong and compact source called Sagittarius A* (pronounced “Sagittarius A-star”).

Beginning in the 1990s, astronomers, including Andrea Ghez at UCLA, were able to use infrared observations to track the motions of large, luminous stars in the vicinity of Sagittarius A*. The observations allowed Dr. Ghez and her colleagues to confirm that the object is massive enough to be a black hole, a result for which she was named a co-winner of the 2020 Nobel Prize in Physics.

Now the Event Horizon Telescope has added a new chapter to the story, providing a direct view of Sagittarius A* that can be connected to other observations and used to test theories of gravity and other astrophysical processes.

“It’s really exciting,” said Daryl Haggard, an astronomer at McGill University who was part of a team that made parallel X-ray satellite observations of the black hole while the Event Horizon Telescope collected data for the image.

“For many of us, Sagittarius A* is the goal that led us to this job,” he added. “Having an exciting result to share about our own galaxy’s black hole is something of a Holy Grail. It’s a highlight.”

Our Morning Update and Evening Update newsletters are written by Globe editors and give you a concise summary of the day’s biggest headlines. Sign up today.