The other half of the universe?

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Science  07 Nov 2014:
Vol. 346, Issue 6210, pp. 696-697
DOI: 10.1126/science.aaa1077

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The history of astronomy has largely been concerned with the study of discrete objects: planets, stars, and galaxies. From such observations, we have discovered the nature and evolutionary histories of these objects. It is natural to ask whether these studies provide a comprehensive picture of the evolution of the universe, or whether large numbers of objects too faint to detect individually or intrinsically diffuse sources may be present. On page 732 of this issue, Zemcov et al. (1) present results from a study of near-infrared background light that reveal that as many as half of all stars have been stripped from galaxies in their many collisions and mergers over the history of the universe. At galactic distances, the stars are faint but can be detected in ensemble through the spatial variations in sky brightness caused by their spatial distributions. It is remarkable that such a major component of the universe could have been hiding in plain sight as an infrared background between the stars and galaxies.