The Wide-field Infrared Survey Explorer was turned off a few months ago, but the science it did lives on. NASA just released a gallery of nine spiral galaxy images taken by WISE, and they’re lovely:
[Click to galactinate.]
Several of my favorite big, grand design spirals are there, like M51, M81, and M83. Note that since WISE only sees infrared light, these are false color images; the colors used are blue for 3.4 micron IR light, cyan for 4.6 microns, green for 12 microns, and red for 22 microns. The reddest light a human eye can see is very roughly 0.75 microns, to give you a comparison. In the images, star-forming regions are yellowish and/or pink, dust (in the form of long-chain organic molecules called polycyclic aromatic hydrocarbons) is green, and old stars are blue.
While looking over the images, I actually recognized the name of the one in the lower right: IC 342 (here’s a full-res WISE shot of it). This is part of a small group of galaxies near our Milky Way that is heavily obscured by dust in our galaxy. I wrote about it a little while back, when I posted a nice picture of it from the NOAO. Here are those two images side-by-side:
They are not perfectly aligned; the WISE image is rotated a few degrees counterclockwise relative to the NOAO image. But you can align some of the features; the pink tendrils to the upper right in the left image can be seen as yellow in the WISE image, for example. The spiral arms are prominent in both pictures, but the WISE image makes the galaxy look more like a spider’s web, the arms interconnected by spurs of material. The structure of spiral galaxies is extremely complicated, and to be honest not as well understood as it could be. There are still serious arguments about how the arms are formed and maintained over billions of years. Images like these in various wavelengths will help us greatly in figuring all that out.
And there’ll be plenty to work with: the folks at WISE plan on releasing a thousand more images like these to help astronomers map out galaxies. I may have to clear my weekend schedule.
Image credits: NASA/JPL-Caltech/WISE Team; T.A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF