A supermassive black hole has kept astronomers glued to their telescopes for years. First there was a surprise disappearance and now an unstable turning act is observed. MIT scientists presented these findings at the 245th meeting of the American Astronomical Society and will publish the results in an upcoming paper in Nature.
The black hole in question is 1ES 1927+654, which has a mass similar to that of a million suns and is located in a galaxy that is 100 million light years away. In 2018, astronomers at MIT and elsewhere observed that the black hole’s corona—a cloud of moving, incandescent white plasma—suddenly disappeared, before reassembling months later.
The brief but dramatic closure was a first in black hole astronomy. Now, Members of the MIT team have detected the same black hole exhibiting unprecedented behavior.
Specifically, astronomers have detected flashes of X-rays coming from the black hole at an increasing rate. Over a period of two years, the flashes, with millihertz oscillations, They increased their frequency from every 18 minutes to every seven minutes. This spectacular acceleration of X-rays had not been observed until now in a black hole.
The researchers explored a number of scenarios to explain the flashes. They believe the most likely culprit is a spinning white dwarf, an extremely compact core of a dead star orbiting the black hole and coming dangerously close to its event horizon, the limit beyond which nothing can escape the gravitational pull of the black hole. black hole.
If this is the case, the white dwarf must be doing an impressive balancing act, given that it could be reaching directly to the edge of the black hole without falling into it.
“This would be the closest thing we know to a black hole,” confirms Megan Masterson, a physics graduate student at MIT who co-led the discovery. Furthermore, he added, “this tells us that objects like white dwarfs can live very close to an event horizon for a relatively long period of time.”
If a white dwarf is the cause of the black hole’s mysterious flash, it would also emit gravitational waves, in a range that would be detectable by next-generation observatories such as NASA’s Laser Interferometer Space Antenna (LISA).
“These new detectors are designed to detect oscillations on the minute scale.”so this black hole system is in that sweet spot,” says co-author Erin Kara, associate professor of physics at MIT.
Masterson and Kara explored models for several astrophysical phenomena that could explain the X-ray patterns they observed, including one possibility related to the black hole’s corona.
“One idea is that this corona oscillates, perhaps moves back and forth, and if it starts to shrink, those oscillations accelerate as the scales get smaller,” Masterson says. “But we are in the early stages of understanding coronal oscillations,” he adds.
A more likely scenario, and one that scientists better understand in terms of the physics involved, involves a reckless white dwarf. “These things are really small and quite compact, and “Our hypothesis is that it is a white dwarf that is getting so close to the black hole.”argues Masterson.
Based on their models, the researchers estimate that the white dwarf’s mass could be about one-tenth that of the Sun. In contrast, the supermassive black hole itself is on the order of a million solar masses.
When an object gets so close to a supermassive black hole, it is expected to emit gravitational waves that bring it closer to the black hole. As you get closer, the white dwarf moves at a faster ratewhich may explain the increasing frequency of X-ray oscillations that the team observed.
The white dwarf is practically on the brink of the abyss and is estimated to be just a few million kilometers from the event horizon. However, researchers predict that the star will not fall into it. While the black hole’s gravity can pull the white dwarf inward, the star is also losing some of its outer shell to the black hole.
This detachment acts as a small kickbackso the white dwarf, an incredibly compact object in itself, can resist crossing the black hole boundary.
“As white dwarfs are small and compact, it is very difficult to dismember them, so they can be very close to a black hole,” says Kara. “If this scenario is correct, this white dwarf is right at the tipping point and we may see it move further away,” he explains.
The team plans to continue observing the system, with existing and future telescopes, to better understand the extreme physics that play out in the innermost environments of a black hole. They are particularly excited to study the system once the LISA gravitational wave detector is launched (currently planned for the mid-2030s), given that The gravitational waves that the system should emit will be at an optimal point that LISA will be able to clearly detect.
“The only thing I have learned with this source is that we should never stop looking at it because it will probably teach us something new,” Masterson concludes. “The next step is just to keep your eyes open.”
*With information from Europa Press
