A property of most clusters of galaxies with redshifts of about 0.4, which show a much higher proportion of late-type spiral and irregular galaxies (disk galaxies) than do similar clusters closer to us. This effect implies a strong evolution of galaxies in the recent past. Many of the disk galaxies must have disappeared from view in the nearby clusters, probably as a result of mergers or by losing their gas. The effect was reported in 1978 by the American astronomers Harvey Raymond Butcher (1947– ) and Augustus Oemler, Jr (1954– ).
Subjects: Astronomy and Astrophysics.