BBC Sky at Night Magazine
Corona reappears – around a black hole
Astronomers have witnessed the demise and rapid rebirth of a black hole’s corona, a new study has revealed.
In 2018, astronomers noticed that the corona – the billiondegree ring of particles surrounding the event horizon – of an otherwise unremarkable black hole was rapidly dimming. “We expect luminosity changes this big should vary over many thousands to millions of years,” says Erin Kara from MIT, who took part in the study. “But in this object we saw it change by a factor of 10,000 over a year, and it even changed by a factor of 100 in eight hours, which is just totally unheard of.”
It’s thought a star straying too close to the black hole caused the dimming; it ricocheted around, dragging the corona particles into the black hole. Then, a few months later, a new corona began forming. “This seems to be the first time we’ve seen a corona first of all disappear, but then rebuild itself, and we’re watching in real time,” says Kara. www.mit.edu