This Spitzer false-color image is a composite of data from the 24 micron channel of Spitzer's multiband imaging photometer (red), and three channels of its infrared array camera: 8 micron (yellow), 5.6 micron (blue), and 4.8 micron (green). Stars are most prominent in the two shorter wavelengths, causing them to show up as turquoise. The supernova remnant is most prominent at 24 microns, arising from dust that has been heated by the supernova shock wave, and re-radiated in the infrared. The 8 micron data shows infrared emission from regions closely associated with the optically emitting regions. These are the densest regions being encountered by the shock wave, and probably arose from condensations in the surrounding material that was lost by the supernova star before it exploded.
The composite above (PIA06908, PIA06909, and PIA06910) represent views of Kepler's supernova remnant taken in X-rays, visible light, and infrared radiation.
Each top panel in the composite above shows the entire remnant. Each color in the composite represents a different region of the electromagnetic spectrum, from X-rays to infrared light. The X-ray and infrared data cannot be seen with the human eye. Astronomers have color-coded those data so they can be seen in these images.