A distant supermassive black hole, the mysterious 1ES 1927+654, emits X-ray pulses unlike anything previously recorded, which MIT astronomers hypothesize results from a cosmic balancing act.
Scientists have been fascinated with this particular black hole for years following the occurrence of a strange event observed by astronomers in 2018. The MIT team behind the discovery reported their findings at the 245th meeting of the American Astronomical Society in National Harbor, Maryland.
Unusual Behavior From A Black Hole
One hundred million light-years away, the black hole 1ES 1927+654 contains the mass of a million suns. The spinning white-hot plasma of its corona was under the watchful eyes of MIT and other institutions in 2018 when that corona mysteriously disappeared and slowly rebuilt itself over several months. Before this, astronomers had never observed a corona coming and going, which eventually developed into the brightest X-ray-emitting object in the sky for a time.
“It was still extremely bright, though it wasn’t doing anything new for a couple years and was kind of gurgling along. But we felt we had to keep monitoring it because it was so beautiful,” said co-author Erin Kara, an associate professor of physics at MIT. “Then we noticed something that has never really been seen before.”
Eyes In Space
Space-based platforms like the James Webb Space Telescope and others have expanded scientists’ access to cosmic data in recent years, leading to rapid increases in our understanding of the universe. Among these, the European Space Agency’s XMM-Newton space-based observatory records X-ray emissions from extreme cosmic sources like black holes, neutron stars, and galactic clusters.
When the MIT team analyzed the XMM-Newton data, they found something intriguing: the black hole’s X-rays appeared to be pulsing with increasing frequency.
“These new detectors are designed to detect oscillations on the scale of minutes, so this black hole system is in that sweet spot,” explained co-author Erin Kara, associate professor of physics at MIT.
MIT astronomers observed the new and unusual behavior of 1ES 1927+654 over the last two years. During that period, X-rays flashed out of the black hole at an increasing pace, increasing from every 18 minutes to as frequently as every seven minutes. Like the lost and found corona, this is the first time observers spotted a rapid speed increase in X-ray flashes from a black hole.
“We’ve never seen this dramatic variability in the rate at which it’s flashing,” Masterson says. “This looked absolutely nothing like a normal black hole.”
Black Hole Hypotheses
“One idea is that this corona is oscillating, maybe bobbing back and forth, and if it starts to shrink, those oscillations get faster as the scales get smaller,” commented Megan Masterson, a graduate student in physics at MIT, who co-led the discovery. “But we’re in the very early stages of understanding coronal oscillations.”
The MIT astronomers generated multiple hypotheses to explain the strange behavior before settling on a spinning white dwarf a tenth the mass of the sun orbiting the black hole’s corona, drawing incrementally closer but tightly maintaining balance on the edge. The flashing occurring in the X-ray band indicates that the source is likely in very near proximity to the black hole.
The inner areas of a black hole are incredibly high-energy environments, leaving X-rays less likely to be picked up at far distances than coming from the cooler area of the accretion disc, which generally emits optical and ultraviolet light instead of X-rays. That close distance to the black hole is estimated to only be a few million miles from the event horizon.
“This would be the closest thing that we know of around any black hole,” said Masterson. “This tells us that objects like white dwarfs may be able to live very close to an event horizon for a relatively extended period of time.”
A Tight Balance
A supermassive black hole is expected to release gravitational waves that pull in any object approaching this close. The closer it gets, the faster the white dwarf moves, which could explain the increasing rate of X-ray oscillations.
Those few million miles represent a fast-approaching precipice of no return, yet the MIT team believes the white dwarf will avoid falling into the cosmic maw. As the black hole’s gravity pulls the star forward, the star sheds its outer layer, pushing the hole away again.
“Because white dwarfs are small and compact, they’re very difficult to shred apart, so they can be very close to a black hole,” Kara says. “If this scenario is correct, this white dwarf is right at the turnaround point, and we may see it get further away.”
Black Hole Observations To Continue
The MIT team will continue their observations, and while existing telescopes provided the fodder for these discoveries, astronomers are looking forward to incoming technological advances that will expand their observations even further.
NASA’s Laser Interferometer Space Antenna (LISA), a space-based gravitational wave detector, planned for a mid-2030s launch, is at the top of their list. The waves the system gives off are ideally situated in the band engineers designed LISA to monitor.
“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. “The next step is just to keep our eyes open.”
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.