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Originally Posted by Star Gazer
I'm having trouble interpreting this picture. The article says 5 galaxies are to be seen. On the right hand side of the green arc I see what look likes two nuclei in one galaxy(I would assume these are the two that are "so beaten up"). On the left hand side I see two large galaxies, one at the top and one at the bottem. Is it the one at the top that is involved in the collision?
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The two nuclei you see belong to two galaxies, NGC7318A on the right, and NGC7318B on the left. The elliptical galaxy at lower right is NGC7317. The deformed spiral galaxy on the left has a tidal tail of stars that extend off to the left, joining a deep red clump at the left edge. That one is NGC7319. Those four galaxies are an interacting group. NGC7318B is colliding with the other galaxies, moving approximately towards us as seen in this picture. That collision is responsible for generating the shockwave that shows up in the image as green. The pink oval galaxy which extends towards the lower left corner is NGC7320, and it is the foreground object. The 4 cluster galaxies are about 270,000,000 light years away, whereas NGC7320 is only about 35,000,000 light years away.
The tidal tail that NGC7319 displays was created in a collison with NGC7320C, which is out of the picture, off to the left. NGC7320C collided with NGC7319 "a few hundred million years ago".
The shockwave is not news, it was seen clearly by Chandra several years ago. It is the presence of so much molecular hydrogen that is news, because H
2 does not normally form in a gaseous reaction, but requires a surface (dust grains, for instance) on which to form. It appears that the rapid cooling behind the shock allows for gas phase formation of H
2, and that is scientific news.