Each galaxy is in a different morphological stage. NGC 1721 is in an intermediate (SBb) barred spiral state, and NGC 1725 is classed as being in a final lenticular stage (SO D). NGC 1728 is classed as a spiral galaxy in its mature stage (Sa D). If you want to delve further into galactic morphology this link, is a very recent (8/2008) and good graphical overview. References also indicate that VV 699 is essentially merged into the NGC 1725 galaxy triplet.
Well, are these galaxies merging, and if so what will be the outcome? The image on the right is another false color actual astro-photograph of merging triplet galaxies. You may click on the image to enlarge it. To see my astrophotograph of the first set of triplets, click here.
So what is the merging process? How does it really happen? This image is from a computer simulation of that process. Follow the process from left to right and top to bottom. The dashed lines indicate the flow pattern of the mergers. Let me tell you, this is just so exciting! Some naysayers say the universe is slowly dying. It will never die, it just keeps on changing, merging, and growing in different ways with enormous displays of power and energy. This process renews me, a mere human, each and every day.
I will stop here to catch my breath, ruminate a bit, and just wallow awhile in all this power and glory. When I come back we will talk more about the merging process and what happens when the inherent black holes CRASH together!! Stay tuned, please.