Most large galaxies are illuminated by billions of stars, but some cosmic monstrosities have an even greater source of light: an active, supermassive, feeding black hole. Physically, the intense outburst heats up and shocks the surrounding matter as the black hole devours matter. After the black hole stops feeding, some intense emission remains, even extending beyond the galaxy's stars. For the first time, we've witnessed a single galaxy brighten and fade in detail: from inactive to active and back. From GALEX (UV) to the VLT (radio) and many other bands, the entire galaxy brightened in the 1980s and faded in the 2010s.

Source: Forbes December 05, 2016 15:02 UTC