Supermassive black holes have riveted astronomers for years, first with their sudden disappearances, then their erratic spinning behavior.
The black hole in question has a mass of 1ES 1927+654, about 1 million times that of the Sun, and resides in a galaxy 270 million light-years away. In 2018, astronomers at MIT and elsewhere observed the black hole’s corona (a swirling cloud of hot, white plasma) suddenly disappear, only to reassemble a few months later. This brief but dramatic halt was a first in black hole astronomy.
Members of a research team at MIT have now discovered a similar black hole that behaves in a way that has never been seen before.
Astronomers have detected a steady increase in X-rays emitted from the black hole. Over the course of two years, millihertz-frequency X-ray radiation increased from every 18 minutes to every seven minutes. This dramatic increase in the speed of X-rays has never been observed from a black hole before.
Researchers have considered several scenarios that could be causing the flash of light. They believe the most likely culprit is a spinning white dwarf, the extremely compact core of a dead star that orbits the black hole and is dangerously close to the event horizon, the boundary where the black hole’s gravity can’t be escaped. If so, the white dwarf must be performing an incredible balancing act, potentially approaching the edge of the black hole without falling into it.
“This may be the closest thing we know to the vicinity of a black hole,” said MIT physics graduate student Megan Masterson, co-leader of the discovery. “It shows that objects like white dwarfs can exist very close to the event horizon for relatively long periods of time.”
The researchers presented their findings today at the 245th Meeting of the American Astronomical Society.
If a white dwarf is the source of the black hole’s mysterious flares, it should also be emitting gravitational waves within the range that next-generation observatories like the European Space Agency’s Laser Interferometer Space Antenna (LISA) can detect.
” These new detectors are designed to detect tiny-scale fluctuations, which makes this black hole system ideally placed,” said Erin Cara, an MIT associate professor of physics and co-author of the study.
Other co-authors on the study include MIT Kavli members Christos Panagiotou, Joheen Chakraborty, Kevin Burdge, Riccardo Arcodia, Ronald Remillard and Jingyi Wang, as well as collaborators from several other institutions.
Nothing out of the ordinary
Kara and Masterson were part of the team that observed 1ES 1927+654 in 2018. At the time, the black hole’s corona darkened and then slowly reformed over time. At one time, the newly formed corona — a cloud of plasma and high-energy X-rays — was the brightest X-ray-emitting object in the sky.
“It’s still very bright, even though there hasn’t been anything new in years and it’s just trickling in, but it was so beautiful that we felt we had to keep following it,” Kara said, “and we noticed something we’d never seen before.”
In 2022, the research team examined observations of the black hole by the European Space Agency’s XMM-Newton, a space observatory that detects and measures X-ray emission from black holes, neutron stars, galaxy clusters, and other extreme cosmic sources. They found that the X-rays from the black hole appear to pulsate with increasing frequency. Such “quasi-periodic oscillations” have only been observed in a handful of other supermassive black holes, where X-rays appear at regular intervals.
Radio images of 1ES 1927+654 show a powerful radio burst followed by structures that look like plasma jets erupting from either side of the black hole at the center of the galaxy. The first images, taken in June 2023, show no sign of the plasma jets, likely because they are hidden from view by hot gas. Starting in February 2024, these features then appeared, expanding outward from the center of the galaxy, covering a total distance of about half a light-year as measured from the center of each structure.
Source: NRAO/Meyer et al. 2025
In the case of 1ES 1927+654, the blinking appeared to steadily increase over a two-year period from every 18 minutes to every 7 minutes.
“We’ve never seen such a dramatic change in blinking rate before – it’s totally different from a normal supermassive black hole,” Masterson said.
The fact that flickering was detected in the X-ray spectrum indicates that its source is likely located very close to the black hole. The deepest regions of a black hole are extremely energetic environments where X-rays are produced by fast-moving, hot plasma. At greater distances, the rotation of the gas in the accretion disk slows down, making it less likely that X-rays will be observed. The cold environment of the disk emits visible light and ultraviolet light, but very little X-ray radiation.
” If you can see something in X-rays, that means you’re pretty close to a black hole,” Kara said. “If you see changes on timescales of minutes, that’s close to the event horizon, and the first thing you think about is circular motion and whether something could be orbiting the black hole.”
X-ray rock ascent
Whatever is producing the X-rays is operating extremely close to the black hole, with researchers estimating it to be just a few million miles from the event horizon.
Masterson and Kara investigated a variety of astronomical models that could explain the X-ray patterns they observed, including the possible involvement of the black hole’s corona.
“One idea is that this corona is oscillating, possibly moving back and forth, and as it starts to shrink, the oscillations will get faster as it gets smaller in scale,” Masterson said, “but we’re still in the very early stages of understanding coronal oscillations.”
Another promising scenario involves a stray white dwarf, for which scientists have a better understanding of the physics involved. Researchers estimate that models suggest that a white dwarf could have a mass about one-tenth that of the Sun. In contrast, the mass of a supermassive black hole itself is about one million solar masses.
When any object approaches such a supermassive black hole, gravitational waves are thought to be emitted that pull the object towards the black hole. The white dwarf would speed up as it approaches, which could explain the increased frequency of the X-ray oscillations the team observed.
The white dwarf is effectively on the brink of no return, estimated to be just a few million miles from the event horizon. But researchers predict it won’t fall. The black hole’s gravity could be pulling the white dwarf inwards, while the star is shedding some of its outer layers into the black hole. This fall could act as a tiny thrust that keeps the white dwarf, an extremely compact object, from crossing the black hole’s boundaries.
“Because the white dwarf is small and dense, it’s hard to tear apart, which is why it could be located so close to the black hole,” Kara said. “If this scenario is correct, then this white dwarf is right at the tipping point, and we could see it moving further away.”
The research team plans to continue observing this system using current and future telescopes to better understand the extreme physics at work in the deepest environments of black holes. They are particularly excited to study this system after the launch of the LISA space-based gravitational wave detector, currently scheduled for the mid-2030s, because gravitational waves emitted from this system will be in an ideal location for LISA to unambiguously detect them.
“One thing I’ve learned from this source is to never stop looking because it’s always going to teach you something new,” Masterson said. “The next step is to keep your eyes peeled.”
