THE CLUSTER OF HYDRA GALAXIES

Galaxies are rarely isolated in space. Most of them belong to clusters, the number of components of which may vary from a few tens to several thousand, connected to each other by mutual gravitational interactions. An example of galaxy clusters is the Local Group, to which the Milky Way belongs, consisting of three large spiral galaxies and many irregular galaxies. Another good example is the Hydra Cluster.

This cluster is located 160 million light-years away in the constellation of the same name. The cluster consists of about 160 components scattered over an area of 10 million light years, making it, after the Virgo and Centaur Clusters, the third largest cluster of galaxies less than 200 million light years from Earth.

The cluster's three largest galaxies, the two elliptical galaxies NGC 3309 and NGC 3311 and the spiral NGC 3312, all have a diameter of about 150,000 light-years. It is believed that these three objects are in an interaction process, which will lead them to merge to form a single giant elliptical galaxy. 

Galaxy mergers are quite common within clusters. For example, thinking of our Local Group, the Milky Way and the Andromeda Galaxy are also destined to merge in about 5 billion years. 

These collisions are not destructive, they only alter the final structure of galaxies. They consist of large empty spaces, and direct collisions between stars are very unlikely.

Credit: Marco Lorenzi, Angus Lau, Tommy Tse.