There is a large black hole at the center of the Milky Way Galaxy called "Sagittarius A". Scientists have been observing Sagittarius A for about 20 years and thought that they new its patterns. The suddenly, in May 2019, while they were observing from the Keck Observatory in Hawaii, Sagittarius A suddenly flared. It became about 75 times brighter than they had ever previously observed.
They are still studying the event to try to determine what caused it. The best guesses so far is that it was caused by a disruption of the matter falling into the black hole either from a passing star or a gas cloud.
The flare lasted about 2.5 hours. The team at the Keck observatory recorded a time lapse video of the event.
This from Universe Today:
Even though the black hole at the center of the Milky Way is a monster, it’s still rather quiet. Called Sagittarius A*, it’s about 4.6 million times more massive than our Sun. Usually, it’s a brooding behemoth. But scientists observing Sgr. A* with the Keck Telescope just watched as its brightness bloomed to over 75 times normal for a few hours.
The flaring is not visible in optical light. It’s all happening in the near-infrared, the portion of the infrared spectrum closest to optical light. Astronomers have been watching Sgr. A* for 20 years, and though the black hole does have some variability in its output, this 75 times normal flaring event is like nothing astronomers have observed before. This peak was over twice as bright as the previous peak flux level.