APOD 28 December 2022 annotated.png
One side of M88 has been truncated by ram pressure.
I used to find M88 a pretty boring galaxy. I mean, just look at it. Its colors are unexciting, its center is small, its arms are unspectacular. What's to like about it?
But look again. One side of it is suspiciously smooth, and the opposite side is more windblown. And this is the key to what has happened to M88.
M88 probably used to look something like NGC 1232:
NGC 1232 Josef Pöpsel Capella Observatory.png
NGC 1232. Credit: Josef Pöpsel, Capella Observatory.
In other words, M88 used to be a lot more wild and crazy, with flamboyant arms and a lot of star formation. Ah, but then the Virgo Cluster happened to it!
Large galaxy clusters kill spiral galaxies by driving their gas out of them. These clusters are filled with a thin but super-hot gas and all sorts of tidal forces, which combine to drive the gas out of spiral galaxies.
M90 with ionized outflow A Boselli et al.png
Large Virgo spiral M90. Its gas is being driven out of it by tidal forces
and ram pressure of the Virgo Cluster. Image: A. Boselli et al.
Eventually, spiral galaxies in large galaxy clusters end up looking like NGC 4921:
Or rather, they end up looking like NGC 936.
Some galaxies are lucky. Sparkling, flamboyantly star forming M61 sits on the very southern outskirts of the Virgo Cluster, unaffected by the vicious conditions further in. And small elegant M74 is not a member of a galaxy cluster at all.
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