What are the most distant active galaxies?
• The quasars appear to be very distant, highly luminous active galaxies. • Astronomers know they are very far away because they have very high redshifts. To be visible at such great distances, they must be ultraluminous. • Because quasars can change their brightness quickly, you can conclude they must be small—only a few times larger than our solar system. • Observations of the spectra of hazy objects near quasars and the spectra of quasar fuzz show that quasars are the active cores of very distant galaxies. • Gravitational lensing by very distant galaxies can form multiple images of quasars, and that shows that the quasars must be even farther away than the lensing galaxies. • Superluminal expansion refers to blobs of material that appear to be rushing away from some quasars faster than the speed of light. This is an illusion caused when a jet points nearly at Earth and does not contradict the modern understanding of quasars. What can active galaxies reveal about the history of the u
