A stunning astronomical phenomenon is captivating researchers as they delve into the enigmatic behaviors of the supermassive black hole known as 1ES 1927+654. This colossal black hole, approximately one million times the mass of our sun, is located in a galaxy 270 million light-years away from Earth. A peculiar disappearance of its corona—a swirling cloud of superheated plasma—was first spotted in 2018, a groundbreaking event in the field of black hole astronomy. After months, this corona astonishingly reformed, keeping astronomers intrigued.
New observations by the MIT research team have revealed even more remarkable behavior from this distant black hole. Astronomers noted a significant increase in X-ray flashes emitted from 1ES 1927+654, which accelerated dramatically over two years. The frequency of these flashes surged from every 18 minutes to an astonishing every 7 minutes, marking an unprecedented rate of changes from a black hole.
Scientists are investigating various theories to decipher the cause of these mysterious flashes. The leading hypothesis suggests that a spinning white dwarf—a remnant core of a deceased star—may be spiraling closer to the black hole’s event horizon, a pivotal boundary from which nothing escapes its gravitational grasp. This precarious proximity raises questions about how this white dwarf can maintain its orbit without being consumed by the black hole.
“This would be the closest we’ve seen anything orbiting a black hole,” states Megan Masterson, a graduate student at MIT who co-led this discovery. “It suggests that white dwarfs can survive remarkably close to the event horizon for extended periods.”
The research team presented their findings at the 245th meeting of the American Astronomical Society and is set to publish their results in an upcoming paper in Nature.
If the X-ray flashes indeed result from the white dwarf’s activity, they are likely producing gravitational waves detectable by advanced observatories like NASA’s future Laser Interferometer Space Antenna (LISA). “These new detectors are built to capture oscillations within minutes, making this unique black hole system a prime candidate for study,” notes co-author Erin Kara, an associate professor at MIT.
An Unusual Star
Masterson and Kara were part of the original team that scrutinized the intriguing behavior of 1ES 1927+654 back in 2018, when its corona dimmed and gradually reformed, becoming the brightest X-ray emitter in the night sky. “Despite its initial stability, we couldn’t lose sight of it because its behavior was so captivating,” Kara explains. “Then, we observed something truly extraordinary.”
In 2022, the researchers examined data from the European Space Agency’s XMM-Newton observatory, which captures X-ray emissions from various cosmic sources. To their surprise, they found that the X-rays from the black hole began to pulse with increasing frequency—what scientists refer to as “quasi-periodic oscillations,” a phenomenon previously witnessed only in a handful of supermassive black holes.
The flickering phenomenon observed in 1ES 1927+654 has been nothing short of astonishing, ramping up frequency from 18 minutes to just 7 over two years. “This level of variability is unprecedented; it defies what we typically expect from a supermassive black hole,” Masterson remarks. The detection of X-ray emissions suggests they originate from very near the black hole. The energetically charged environment within and around the black hole produces X-rays primarily due to fast-moving hot plasma, whereas a cooler accretion disk further out emits other light forms, like optical or ultraviolet.
Decoding the X-ray Mystery
The researchers speculate that whatever is creating these X-ray signals lies extremely close to the black hole—potentially within just a few million miles of its event horizon. Masterson and Kara analyzed various astrophysical models to determine the cause of the observed X-ray behavior, including theories related to the black hole’s own corona.
“One possibility is that the corona experiences oscillations and if it begins to diminish, these oscillations could quicken, yet we’re still working to understand coronial oscillations deeply,” Masterson notes. However, another explanation may lie with the white dwarf. According to their estimations, the white dwarf could be about one-tenth the mass of the sun, whereas the supermassive black hole weighs in at around one million solar masses.
As any object approaches the event horizon of a supermassive black hole, it is expected to emit gravitational waves, which would pull the object closer. As the white dwarf orbits, it accelerates, further explaining the increased frequency of the detected X-ray oscillations.
Remarkably, the white dwarf seems to be dancing on the edge of annihilation, situated just a few million miles from the event horizon. However, researchers speculate it isn’t about to plunge into the abyss; rather, as the black hole’s gravity attempts to draw the star inward, the white dwarf releases some of its outer layers into the black hole—a phenomenon acting as a kick-back that enables the star to resist crossing that perilous boundary.
“White dwarfs are compact and resilient, making them tough to destroy, allowing them to orbit supermassive black holes without falling in,” Kara adds. “If our theory is valid, this white dwarf is at precarious juncture, and we might even witness it moving further away.”
The research team looks forward to continuing their observations of this captivating black hole system using both existing and future telescopes. They’re particularly keen to study it when LISA, the upcoming space-based gravitational-wave observatory, launches, anticipated in the mid-2030s, as it may capture the gravitational waves produced by this system.
“The intriguing takeaway from studying this source is to keep observing, as it may unveil astonishing discoveries,” Masterson concludes. “The next step is to stay vigilant.”
Photo credit & article inspired by: Massachusetts Institute of Technology
