Clusters of galaxies are the largest entities known and studied in the Universe. They are also very luminous, with integrated brightnesses rivalling those of quasars. This property, along with their radio and X-ray emission, enables them to be discovered and investigated at large distances. It is generally hoped that this will lead to the use […]
Rich clusters of galaxies are certainly not due to chance associations or random encounters between galaxies. They are systems in which galaxies are dynamically interacting with each other and with any intracluster gas. In terms of the spatial distribution of member galaxies the richest clusters especially appear stable and gravitationally bound. Unlike the Solar System […]
Several rich clusters are known in the southern hemisphere, and one of the most prominent lies in the constellation of Centaurus. Some tens of its member galaxies have had redshifts measured and the mean of 3740kms-1 implies a distance of about 50Mpc. The velocity dispersion is about 950 kms-1 . The distribution of galaxies in […]
Sixteen of the 34 galaxies listed in the Messier catalogue are members of the Virgo cluster, which lies near the north galactic pole and is a good example of an irregular cluster Its mean redshift translates to about 1140 km s-1 implying a distance of only 16Mpc, and the spread in velocities is about 670 […]
The rich cluster in Perseus lies much nearer to the galactic plane than the Coma cluster, so has not been so well studied. Moreover it is not as symmetrical, the brightest galaxy members lying in an east-west line. It is possible that this projected line, which stretches for about 1°, is a transient effect observed […]
One of the nearest rich regular clusters is situated two degrees from the north galactic pole in Coma Berenices . It is ideally situated for observation, and the effects of galactic obscuration may be ignored. The cluster extends over several degrees, its total radius being difficult to define. Galaxies are usually assigned to a cluster […]
Most of the clusters we describe are termed RICH CLUSTERS of galaxies. This implies a fairly high degree of central concentration of galaxies. Abell’s catalogue tabulates 2712 rich clusters, which are numbered in order of increasing right ascension preceded by the letter A: examples are the Coma and Perseus clusters, A426 and respectively . Abell […]
Galaxies are not distributed randomly on the sky . There are clear gaps where the plane of the Galaxy obscures our line of sight. It can be shown without doubt that the probability of obtaining by chance the observed distribution of galaxies on the sky is negligible. Studies of the clumping for galaxies of different […]
The distribution of galaxies in the sky is far from uniform. The Herschels remarked on the unevenness of the distribution of nebulae on the celestial sphere in the nineteenth century. Part of the variation is due to the uneven distribution of obscuring matter in our Galaxy, and there is a ZONE OF AVOIDANCE at low […]
It we were to be really pedantic we could assert that a normal galaxy is an abstraction: all galaxies, when inspected sufficiently closely, deviate from the norm. Most of the peculiarities are minor, but there are quite a few puzzling ones. An important class of PECULIAR GALAXIES are those which were originally normal but have […]