Reading the ripples. Subtle signals suggest that some of the cosmic microwave background originates in our solar system.

Not-So-Cosmic Microwaves?

Staff Writer

In the past 2 years, astrophysicists and cosmologists have nailed down the age and composition of the universe by studying the all-pervading radiation left over from the big bang. But subtleties in that cosmic microwave background (CMB) suggest that our own solar system may be producing or absorbing some of the microwaves, a team of astrophysicists reports. If the finding holds up, researchers may have to rethink their theory of how the universe ballooned into existence.

The radiation in the CMB has lingered since atoms first formed some 300,000 years after the big bang, stretching to ever-longer wavelengths as the universe expanded and cooled. The CMB now has an average temperature of 2.7 kelvin, but the precise temperature varies by a few millionths of a degree from place to place on the sky. Two years ago, researchers working with NASA's Wilkinson Microwave Anisotropy Probe (WMAP) mapped those temperature variations in exquisite detail (ScienceNOW, 11 February 2003 ). Cosmologists then used the data to confirm predictions of a theory called inflation, which assumes that the infant universe expanded many times faster than the speed of light. They determined that only 27% of our universe consists of matter, and the rest consists of dark energy that stretches across space.

A new analysis suggests that some of the radiation may originate closer to home. Much as orchestral music can be broken down into individual notes low and high, the variations in the intensity of the CMB can be sorted into longer and shorter undulations. Cosmologist Glenn Starkman of Case Western Reserve University in Cleveland, Ohio, and colleagues studied two of the longest kinds of undulations--those that, roughly speaking, span either an eighth or a quarter of the sky, as they report in the 26 November Physical Review Letters.

Such variations can be described by a handful of vectors. Curiously, all but one of the vectors lie in the plane of the solar system and point roughly along the line connecting Earth and sun at either equinox. The researchers estimate the chances that the alignments are coincidental at less than 2 in 1000. If the alignment isn't a fluke, Starkman says, the finding suggests that something within the solar system may be emitting or absorbing microwaves. That would mean the strength of the undulations in the truly cosmic radiation wouldn't jibe with the predictions of inflation and "point to some serious problem with our understanding of the universe at the largest scales," Starkman says.

But the intriguing correlations may still be a product of chance, says Charles Bennett, a cosmologist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and leader of the WMAP team. "Improbable things happen all the time," Bennett says. "It's not quite fair to take the results of an experiment, take out the unusual things, and highlight them."

Related sites
The abstract of the paper
The Wilkinson Microwave Anisotropy Probe Web site
An introduction to the CMB and cosmology

Posted in Space, Physics