Also known as G34.7-0.4, W44 is an expanding supernova remnant that is interacting with dense interstellar material that surrounds it. X-rays from Chandra (blue) show that hot gas fills the shell of the supernova remnant as it moves outward. Infrared observations from the Spitzer Space Telescope reveal the shell of the supernova remnant (green) as well as the molecular cloud (red) into which the supernova remnant is moving and the stars in the field of view.
Image Credit: X-ray: NASA/CXC/Univ. of Georgia/R.Shelton & NASA/CXC/GSFC/R.Petre; Infrared: NASA/JPL-Caltech
Explanation from: http://chandra.si.edu/photo/2015/archives/more.html