Nature 490, 514–516 (2012)

Credit: © NASA/CXC/SAO/J.DEPASQUALE/JPL-CALTECH/STSCI

By using infrared space telescopes to measure the cosmic near-infrared background radiation, we are peering ever deeper into our past. Masking bright sources is one way of measuring this background, which is stronger than that expected from known galaxies. This excess radiation is thought to originate from cosmic sources created in the early Universe when massive stars and galaxies first formed, and from faint dwarf galaxies that are closer to Earth. Moreover, fluctuations in the brightness provide information on the number and distribution of the sources. Asantha Cooray and co-workers have analysed recent data taken by the Spitzer Deep, Wide-Field Survey, covering a vast 10.5 square degrees of the sky. They suggest an alternative infrared origin.

The authors confirm previous claims that, based on more spatially limited surveys, the fluctuations are ten times stronger than any radiation expected from primordial and dwarf galaxies combined. However, rather than seek new sources, Cooray et al. argue that the excess radiation arises from nearby stars within the dark-matter haloes that surround galaxies. These are stars that have been stripped from their parent galaxies during tumultuous galaxy mergers and collisions (pictured). The authors predict optical background light fluctuations with a similar clustering distribution.