This is one of my favorite pictures of the entire year: a composite view of our neighbor the Andromeda galaxy, seen in both the far-infrared and in X-rays.
The IR part (colored orange) was taken by the space-based Herschel telescope, and shows cold, cold dust. Even though this dust is just a few degrees above absolute zero, it still emits feebly in the infrared; the power of the telescope coupled with the relatively small distance to the galaxy make it easier to spot.
The X-ray part of the picture (in blue) couldn't be more different. Taken with the orbiting Chandra Observatory, it shows the hottest, most violent objects in the galaxy: black holes gobbling down matter, gas heated to millions of degrees by dense, whirling neutron stars, and the high-energy radiation from stars that have exploded, sending out vast amounts of material that slam into surrounding gas, creating shock waves that heat the gas tremendously, generating X-rays.
I love the color contrast in this image, the fact that we're seeing entirely different populations of objects, and also the simple idea that this is such a strange view of the Andromeda galaxy, a huge spiral so bright and close it's easily visible to the unaided eye from a dark site. I've seen it countless times with my own eyes, through binoculars, and with telescopes, but never like this. Sometimes, seeing an old friend with different eyes is a great way to be reacquainted with it.
Image credit: IR: ESA/Herschel/PACS/SPIRE/J.Fritz; X-ray: U.Gent/XMM-Newton/EPIC/W. Pietsch, MPE