INTERPRETATIONIf the quasar red shifts obey the same red-shiftÐdistance law as do the galaxies (see extragalactic systems),
their distances can be calculated from their red-shift recessional velocities by the equation v = HVd, where HV is a constant of proportionality, known as Hubble's constant, that is currently estimated to be 55 ± 7 km/sec/megaparsec, and d is the distance of the object. If this interpretation is correct, most of the quasars are more distant than any known galaxy. Hence they are the most distant known objects in the universe and are said to be cosmologically distant.Efforts are under way to find distances to quasars independently of their red shifts. Some quasars appear to be located within clusters of galaxies and show the same red shift as the galaxies. These quasar distances are almost certainly cosmological and presumably correct. A conflict is presented, however, by some observations apparently showing that galaxies lying almost in the same line of sight with certain quasars but having different red shifts are interacting with those quasars. Such interactions would imply that the quasars in question are not as far away as had been thought. Some patterns in the values of observed red shifts also do not seem to be accounted for in terms of standard cosmologies.Despite these anomalies, most astronomers use the concept that quasars lie at apparent cosmological distances and are violently active galactic nuclei (AGN) containing massive black holes and that they are probably closely related to Seyfert galaxies and other radio galaxies. (The fact that clusters of quasars have been observed further suggests that even at an early era the matter of the universe began to gather in clumps; see cosmology.) Even for these astronomers, however, the true galactic nature of quasars remains far from settled. That is, photographs of 35 quasars taken by the Hubble Space Telescope in the mid-1990s revealed their host galaxies to be of many shapes and sizes, including normal spirals such as our own, the problem being that no pattern of violent host galaxies emerged from the study.