Astronomers Found Strange, Accelerating X-Ray Pulses Coming From a Black Hole. They Might Be a Sign of an Orbiting White Dwarf

A supermassive black hole in a distant galaxy is once again surprising scientists.

In 2018, a black hole called 1ES 1927+654, located about 270 million light-years away from Earth, showed its first signs of mysterious behavior. Its corona—the billion-degree cloud of plasma that envelopes it—suddenly disappeared and reappeared. Now, a team of scientists at MIT have observed another novelty: X-ray radiation is emanating in pulses from the black hole with increasing frequency.

Between 2022 and 2024, these flashes shifted from happening roughly every 18 minutes to occurring every 7.1 minutes. Just as its 2018 disappearing act was unprecedented at the time, the black hole’s current behavior marks the first time scientists have witnessed so dramatic a rise in pulses.

“It was exciting in and of itself just to find these oscillations, because it’s only one of a handful [of supermassive black holes that do this],” says lead researcher Megan Masterson, an astrophysicist at MIT, to New Scientist’s Alex Wilkins. “But I think the most exciting thing to us was that the oscillation period—how fast these oscillations were happening—was changing on human-observable timescales, which is not usually what we see around supermassive black holes.”

The researchers presented their work on Monday at a meeting of the American Astronomical Society. The findings are set to be published in Nature in early February, and a pre-print paper, which has not yet been peer-reviewed, is currently available.

The scientists say the most likely culprit behind the mysterious pulsing is a white dwarf—a dense stellar remnant about the size of the Earth—that’s teetering precariously close to the black hole. The white dwarf could be shedding matter and triggering the pulses observed by the researchers. As it circles closer and closer to the black hole, they hypothesize, those pulses speed up.

Now, the white dwarf might be orbiting within millions of miles of the black hole’s event horizon—the point beyond which no matter or light can escape.

“This would be the closest thing that we know of around any black hole,” Masterson says in a statement from MIT.

To skirt so closely around the black hole without being swallowed up is a feat that other cosmic objects, such as a small black hole or a regular star, would not be able to achieve, per a statement from NASA. This helped give the team confidence that they were dealing with a white dwarf.

As the black hole pulls the stellar remnant inward, the white dwarf loses matter from its outermost layer. The shedding of that material, the researchers say, provides a kick-back force in the opposite direction, preventing the white dwarf from falling into the black hole.

While there could be other explanations for the mysterious X-ray patterns, such as oscillations in the black hole’s corona, those are less understood. But to confirm their white dwarf hypothesis, the MIT team will need to detect gravitational waves emanating from the black hole. To do so, they’ll have to wait for the 2035 launch of LISA (Laser Interferometer Space Antenna), the first space-based observatory dedicated to detecting the gravitational waves produced by black holes and other powerful phenomena in the universe.

But if astronomers determine a white dwarf is indeed causing the pulses, it could make the site more desirable for LISA to observe. “Everyone really wants to see a white dwarf get eaten by a black hole with LISA,” Matt Nicholl, an astrophysicist at Queen’s University Belfast in Northern Ireland who was not involved with the work, tells New Scientist. “It helps tremendously if we have a few candidates.”

In the meantime, astronomers will keep their telescopes pointed on the black hole. “The one thing I’ve learned with this source is to never stop looking at it, because it will probably teach us something new,” Masterson says in the statement. “The next step is just to keep our eyes open.”

Sara Hashemi | READ MORE

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.