One possible explanation is that the corona is oscillating. But the researchers believe the most likely culprit is a spinning white dwarf—an extremely compact core of a dead star orbiting around the black hole and getting closer to its event horizon, the boundary beyond which nothing can escape its gravitational pull. Circling closer would mean moving faster, explaining the increasing frequency of x-ray oscillations.
If this is the case, the white dwarf could be coming right up to the black hole’s edge without falling in. “This would be the closest thing we know of around any black hole,” says Megan Masterson, a graduate student in physics at MIT, who reported the findings with associate professor Erin Kara and others.
If a white dwarf is at the root of the mysterious flashing, it can also be expected to give off gravitational waves, detectable by next-generation observatories such as ESA’s Laser Interferometer Space Antenna (LISA). Its launch is currently planned for the mid-2030s.
“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.
