Credit: NASA/JPL-Caltech/UC Irvine

This image shows a portion of our sky, called the Botes field, in infrared light. Using Spitzer, researchers were able to detect this background glow, which spreads across the whole sky, by masking out light from galaxies and other known sources of light.

The scientists find that this light is coming from stray stars that were torn away from galaxies. When galaxies tangle and merge -- a natural stage of galaxy growth -- stars often get kicked out in the process. The stars are too faint to be seen individually, but Spitzer may be seeing their collective glow.