No. 13: Winter 1981
Halton Arp, of the Mount Wilson and Las Campanas Observatories, has discovered three more pairs of galaxies that seem to threaten that cornerstone of astronomy, the redshift distance scale. The new pairs are all in the Southern Hemisphere and, like others on Arp's list, seem to be interacting physically. For example, the filaments of one pair member seem to reach out and connect with the companion. Surely, these dynamically connected galaxies should be equidistant from earth. Such distances are measured by the object's redshift, which is supposedly proportional to its recessional velocity. Thus, each member of a pair should have the same redshift. This does not occur with these three pairs. In one pair, the recessional velocity appears to be 4,600 km/sec for one galaxy and 37,300 km/sec for the other. Arp's conclusion is that at least some of the redshift must be intrinsic; that is, not due to recessional velocity alone. If this is true, the basic cosmological distance scale is suspect.
(Anonymous; "X-ray Quasars Fit Theories ...But Some Galaxies Refuse to Play Ball," New Scientist, 88:22, 1980.)
Reference. For more on discordant redshifts, see AWB7 and AWO4 in our Catalog: Stars, Galaxies, Cosmos, which is described here.