This article was useful to me because I learned that a "blazar" is a thing.

Blazars are one of the brightest of a class of objects called active galactic nuclei (AGN), which are supermassive black holes (SMBHs) in the centers of galaxies. They are active due to the presence of a disk or sphere of ionized gas around them which "fuels" the emission seen at many wavelengths. Blazars emit powerful relativistic jets bright enough to be seen across the universe.