They belong to the radio-loud group of active galactic nuclei, and are powered by energy being pulled into a supermassive black hole.
The STACEE detector in New Mexico observes Cherenkov radiation from one of these objects, specifically Markarian 421. The EGRET catalog, which documents gamma ray sources, lists (*) 66 of them in total, and several other possible candidates will be observed by the GLAST mission. Their relativistic jets often omit radiation that is blue-shifted. They belong to the radio-loud group of active galactic nuclei, and are powered by energy being pulled into a supermassive black hole. FTP name these objects which can be divided into optically violent variables and BL Lac objects, which can also be quasars and thus have a similar-sounding name.
The STACEE detector in New Mexico observes Cherenkov radiation from one of these objects, specifically Markarian 421.
blazars (prompt on "quasars" before the asterisk)