If you thought the Lagoon yesterday was pretty, then reset your awe-meter. Check. This. Out.
D’ya like that? Huh? Do ya? Had enough? No? Then check THIS out!
Those magnificent images are of the galaxies NGC 4402 and NGC 4522, respectively, as seen by the Hubble Space Telescope’s Advanced Camera for Surveys (from before the recent repair mission). They’re both spiral galaxies in the Virgo Cluster, the nearest large collection of galaxies to us, roughly 60 million light years from Earth.
If they look funny to you, then good! The Virgo Cluster is massive, and has a lot of gravity. The galaxies bound to it are moving like bees surrounding a hive, each in its own orbit going every which way. These galaxies are screaming through the cluster at speeds of 10 million kilometers per hour, a truly terrifying velocity.
There is an ethereal gas distributed between the galaxies called the intercluster medium. It’s incredibly thin, but over the size of a galaxy — especially when said galaxy is barreling through it at such tremendous speed — the gas can exert significant pressure, called ram pressure. The pressure is actually blowing the galaxies’ internal gas clouds out into the cluster itself, making them look a little bit like pickup trucks driving down a highway with dirt copiously pouring out the beds*. This is especially obvious in NGC 4522 (the lower one), where you can see bright blue splotches, which are regions of intense star formation, along with dark lanes of dust actually above the galactic plane.
In NGC 4022, you can see how the ram pressure is roiling up the dust in the galaxy, and also blowing it back, though apparently not as briskly as in the other galaxy.
These pictures are incredible. Poke around them; you can see amazing detail in the galaxies themselves, as well as hundreds, maybe thousands of background galaxies.
It’s been a while since we’ve seen deep, glorious pictures of spiral galaxies from Hubble. Now that ACS is working again, and it’s being joined by the equally powerful Wide Field Camera 3, we’ll be seeing lots more of these. Get used to it.
Image credits: NASA and ESA.