Three days ago, reports emerged that scientists had seen a a black hole suddenly disappear and then reappear. According to scientists, the object’s brightness swiftly changed brightness in a way that would normally be expected to take millions of years.

The disappearance and reappearance has never been seen before, and there is yet to be an explanation given by experts, about the occurrence.

“We expect that luminosity changes this big should vary on timescales of many thousands to millions of years,” says Erin Kara, assistant professor of physics at MIT. “But in this object, we saw it change by 10,000 over a year, and it even changed by a factor of 100 in eight hours, which is just totally unheard of and really mind-boggling.”

Though black holes are obviously black, they can be seen by their “corona” that is found around their edge or event horizon. The corona is made up of high-energy particles that shine brightly across the universe, and are heated to intense temperatures.

Scientists speculate that corona was destroyed, with the objects falling into the black hole itself, leading to the sudden and inexplicable dip in brightness. It then managed to come back over time as the black hole pulled material back to its edge to form a new corona, almost as bright as it was before.