The fact that the luminosity of these objects varies on a timescale of weeks or months combined with the fact that they shine continuously implies that they are powered by the gravitational energy of matter accreting onto super-massive black holes.
Lintott et al. proposed that Hanny's Voorwerp represents the first observation of a "light echo" from one of these objects, which is thought to have ejected matter from the adjacent IC 2497. Examples of these objects that are older than the re-ionization epoch are seen through an intervening medium that is largely neutral hydrogen, in contrast to more recent examples of these objects that display a (*) Lyman Alpha Forest. The fact that the luminosity of these objects varies on a timescale of weeks or months combined with the fact that they shine continuously implies that they are powered by the gravitational energy of matter accreting onto super-massive black holes. For 10 points, name these distant active galactic nuclei whose name derives from their extremely high energy output in combination with a point-like emission spectrum.
Lintott et al. proposed that Hanny's Voorwerp represents the first observation of a "light echo" from one of these objects, which is thought to have ejected matter from the adjacent IC 2497.
quasars (prompt on "active galactic nuclei" before mention)