New Type of Cosmic Background

Monday, September 26, 2011

New Type of Cosmic Background

A team of scientists using a sensitive balloon-borne instrument has found an unexplained hiss of relatively low-frequency radio pervading the universe. The discovery represents yet another type of "cosmic background radiation" - distant emission coming from everywhere on the sky - to go along with the backgrounds previously discovered in microwaves, infrared light, X-rays, and gamma rays.

Team leader Alan Kogut (NASA/Goddard Space Flight Center) calls it "exciting evidence for something new in the cosmos." But no one knows yet what it may be. Kogut and his colleagues built and flew an instrument named ARCADE: Absolute Radiometer for Cosmology, Astrophysics, and Diff use Emission, seen at right just before launch.

They hoped to detect highly red shifted radio emission from the first generation of stars. Instead, ARCADE found an excess of lower-frequency radio waves(3 to 8 gigahertz) coming from every where on the 7% of the celestial sphere it surveyed.

"If the result holds up, it is quite interesting," says cosmologist Gary Hinshaw (NASA/Goddard). "It either means that radio galaxies, or some class of radio galaxies, have different properties than were previously thought, or perhaps there is some other, more exotic mechanism for producing radio emission in the universe."

In the symbolic illustration at left, ARCADE looks back through the Milky Way (starry band) to other galaxies, the cosmic web of distant galaxy clusters, the "reionization era" (gray band; one guess is that the new radio background comes from there), to the first super stars and quasars lighting up at the end of the Dark Ages several hundred million years after the Big Bang.