The super-massive black hole at the center of our galaxy, known as Sagittarius A*, briefly increased its brightness by 75 times in May. The news of this discovery has only now been released.
A couple of explanations have been proposed for this unprecedented brightening. These involve objects passing near the black hole disrupting the distribution of matter surrounding it.
It is such surrounding matter than emits light; the black hole itself is invisible. It seems a great deal of sudden, short-term luminosity to explain in this way.

Linked below is an article with further information, including a link to the paper on this discovery, which will soon be published in a scientific journal, and a crude motion picture of the flare-up.

https://www.sciencealert.com/our-galaxy-s-supermassive-black-hole-just-mysteriously-got-really-really-bright