This object is one of the densest known galaxy clusters, located almost 200 million light-years away in the constellation of Serpens. The group was discovered by Dr. Carl Seyfert in 1951. All of the galaxies are crowded into an apparent span of 2 arc-minutes. 

This object is nicknamed “Seyfert’s Sextet”.  Sextet means six.  But looking closely, you will only see 5 galaxies.  The plume at top left was thought in the past to be a 6th galaxy.  But it is now believed to be a tidal tail of stars flung out from 79b.

Of the 5 galaxies, only 4 are at the same distance and are interacting.  The small face-on galaxy, 79e, is much further away at 1 billion light years.

The 4 interacting galaxies (all visible as edge-on cores) are surprisingly small. They are all on the order of 35,000 light years in diameter.  The distant galaxy, 79e, is much bigger in actual size at 60,000 light years in diameter.

It is interesting to visually compare this compact cluster with another, Stephan's Quintet. Scientists say that Seyfert’s Sextet is a more evolved version of Stephan’s Quintet. In an interesting 2007 paper (Seyfert's Sextet: A Slowly Dissolving Stephan's Quintet?, by Durbala et al) they state that Seyfert’s Sextet is 2-3 billion years more evolved than Stephan’s Quintet. The Sextet galaxies have been more disrupted, with more stripped stars and star streams.

For me, the question which arises from studying both of these objects is: Will the galaxies eventually merge to form a single giant elliptical galaxy? This has always been the common thought. I have always thought of these galaxies as mashing and crashing together in a spectacular collision of forces, eventually bashing themselves into a huge fuzzy elliptical galaxy ball. But like most things in astronomy, life is not that simple. Studies indicate that the merger process is more of a slow grinding dissolution, one star at a time. During this dissolution process the gas is stripped out, so star formation stops. Over time it is logical that gravitational forces would reshape the remains into an elliptical, but if that is true, why is it that less than 10% of compact galaxy groups have a first ranked elliptical? ("First ranked" means the most luminous galaxy in the group). It is likely that these mergers take much longer than we intuitively think. In fact, some scientists feel that most compact galaxy groups that ever formed, such as Seyfert’s Sextet and Stephan’s Quintet, are still in existence and are still in the slow process of merging.

Which raises another question - are all of the huge ellipticals the result of galaxy mergers, as commonly thought, or could some of them originally formed that way? It seems logical that galaxies originally form as spiral galaxies, some of which then combine to form huge elliptical galaxies. But we see a lot of large ellipticals, few of which seem to be in a merger-end state.  Perhaps some elliptical galaxies simply form initially as elliptical galaxies, through a mechanism that is not yet clear to us.