Spiral galaxies are among the most magnificent objects in space. Grand and sprawling, they are icons of the night sky.
Like a snapshot of coins tossed in the air, we see them at all angles, from face-on disks to nearly edge-on lines. And sometimes we catch them so precisely to the side that what we see is hard to believe is real. But then we get pictures like this one from Hubble of the galaxy NGC 4452:
[Click to galactinate, and yes, you really want to.]
There are lots of edge-on galaxies in the sky, like NGC 253 and NGC 4710, but this one is extraordinary. The alignment is perfect, and the disk is incredibly thin. Our Milky Way is 100,000 light years across and 2500 or so light years thick (a ratio of 40:1), but NGC 4452 looks even thinner than that; measuring off the picture I get a width-to-thickness ratio of 100:1.
Other things are obvious, too, and honestly a bit weird. For one thing, the central bulge of the galaxy is very small; in most edge-on galaxies it pokes above and below the disk like in NGC 4565, shown here. In that picture you can also see lots of dark dust; that’s actually complex organic molecules that are very efficient at absorbing visible light. They’re created when stars are born and when they die, and dust clouds tend to huddle close to the center of the disk.
[Note added later: It occurs to me there might be dust in the galaxy despite what I say in the next paragraph. That's because dust doesn't show up in the infrared very well, and one of the filters used was IR (as I note in a following paragraph). Also, the kind of camera used isn't as sensitive in the blue as it is in the IR, so that might also suppress seeing any dust that might be there. So take the next paragraph with -- haha -- a grain of salt.]
But NGC 4452 appears denuded of dust! I’ve never seen a galaxy quite so clean. I think it would actually pass the white glove test. Read More
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.