Eye on the sky. The Cosmic Background Imager has captured the most detailed images yet (inset) of the polarization of the cosmic microwave background.

A Slanted View of the Early Universe

In the Atacama Desert of northern Chile, a microwave telescope has taken the best snapshot of an exquisitely faint echo of the big bang. In a paper published online by Science today, astronomers present detailed pictures of the polarization of the cosmic microwave background (CMB)--the faint and ubiquitous image of the fiery universe when it was less than 400,000 years old.

Researchers can paint a "very clean picture" of the young cosmos' structure by studying the polarization of photons coming from different patches of sky, explains team member Carlos Contaldi, an astrophysicist at the Canadian Institute for Theoretical Astrophysics in Toronto. That's because a photon retains the imprint of the last few times it scatters off the cloud of glowing gas in the infant universe. The imprint is reflected in the photon's orientation, or polarization.

The telescope, known as the Cosmic Background Imager, has been observing the CMB for years in hopes of testing theories about how the universe was born. Two years ago, the imager presented what was then the best picture of the CMB (ScienceNOW, 23 May 2002). Even after the Wilkinson Microwave Anisotropy Probe (WMAP) blew most of its competition out of the water with its high resolution images of the CMB across the entire sky (ScienceNOW, 11 February 2003), the imager still held an edge in observing very small features in the CMB.

Now, the imager team has released the results of nearly 2 years of observing polarization in the CMB--the extremely hard-to-spot directionality of incoming light. First detected by another instrument in 2002 (ScienceNOW, 20 September 2002), the polarization paints a sharp picture of the early universe, as it remains relatively unchanged during a photon's multibillion-year journey to Earth. "It shows that [the primordial gas] was behaving exactly as we expected it to behave," says team member Anthony Readhead, an astronomer at the California Institute of Technology in Pasadena.

Even stronger confirmation is expected when WMAP releases its own polarization results, probably within weeks, and other ground-based experiments follow suit. But the imager will still provide data about features in the CMB that are too small for the other experiments to resolve.

Related sites
The Sciencexpress paper
The Cosmic Background Imager