Galactic Groups and Clusters
Galactic Groups and Clusters
A "galactic group" is a collection of galaxies, typically fewer than 50, bound together by mutual gravity. Larger collections are called galaxy clusters and even larger structures being superclusters. Our own galaxy, the Milky Way, is part of the Local Group, which includes over 50 other galaxies.
This is a image of the M81 Group of galaxies, which comprises Bode's Galaxy (M81) towards the top, the Cigar Galaxy (M82), to the left and the Garland Galaxy (NGC 3077) to the right.
M82 is known as a starburst galaxy, due to its exceptional rate of star formation. This starburst activity is thought to be due to its interaction with the neighbouring Bode's Galaxy. Tidal forces caused by gravity have deformed M82, a process that started about 100 million years ago. This interaction has caused star formation to increase tenfold compared to "normal" galaxies. The starburst activity of M82 can be seen by the red filaments extending outwards from the centre of the galactic disc.
Although M81 and M82 are popular targets for astrophotographers, NGC 3077 is certainly worth a closer look. This galaxy is a disrupted elliptical galaxy probably as a result of gravitational interaction with its 2 larger neighbours. Its unique appearance is attributed to the presence of bright, young star clusters and nebulae scattered throughout its intertwined spiral arms, creating a garland-like effect.
Markarian's Chain is a stretch of galaxies that forms part of the Virgo Cluster. When viewed from Earth, the galaxies lie along a smoothly curved line. Charles Messier first discovered two of the galaxies, M84 and M86, in 1781. The other galaxies seen in the chain were discovered by William Herschel. It was ultimately named after the Armenian astrophysicist, Benjamin Markarian, who discovered their common motion in the early 1960s. Member galaxies include M84 (NGC 4374), M86 (NGC 4406), NGC 4477, NGC 4473, NGC 4461, NGC 4458, NGC 4438 and NGC 4435.
The bright members of the chain are visible through small telescopes. Larger telescopes can be used to view the fainter galaxies . Near the centre there appear the pair of interacting galaxies NGC 4438 and NGC 4435, about 50 million light-years away, known as Markarian's Eyes.
The Leo Triplet (also known as the M66 Group) is a small group of galaxies about 35 million light-years away in the constellation Leo. This galaxy group consists of the spiral galaxies M65, M66, and NGC 3628.
The Leo Quartet - also known as the Hickson 44 Compact Galaxy Group. NGC3190, NGC3187, NGC3193 and NGC3185.
The M105 cluster; comprising 5 galaxies; M95, M96, M105, NGC3384 and NGC3389; in the constellation of Leo.
This is an image of a large cluster of galaxies known as the Coma Cluster, which itself forms part of a super cluster of galaxies in the constellation of Coma Berenices.
The cluster's mean distance from Earth is 321 million light years. The central region is dominated by two supergiant elliptical galaxies: NGC 4874 and NGC 4889. Most of the galaxies that inhabit the central portion of the Coma Cluster are ellipticals. Both dwarf and giant ellipticals are found in abundance in the Coma Cluster.
In order to give a feel of the sheer number of galaxies that are in this field of view, I have added an annotated version of the top image, where the galaxies present are labelled with their catalogue designations