04/30/2001 07:00:00

New Analysis of BOOMERANG Data Uncovers Harmonics of Early Universe

Cosmologists from the California Institute of Technology and their international collaborators have discovered the presence of acoustic "notes" in the sound waves that rippled through the early universe.

The existence of these harmonic peaks, discovered in an analysis of images from the BOOMERANG experiment, further strengthens results last year showing that the universe is flat. Also, the new results bolster the theory of "inflation," which states that the universe grew from a tiny subatomic region during a period of violent expansion a split second after the Big Bang.

Finally, the results show promise that another Caltech-based detector, the Cosmic Background Imager (CBI), located in the mountains of Chile, will soon detect even finer detail in the cosmic microwave background. Analysis of this fine detail is thought to be the means of precisely determining how slight fluctuations billions of years ago eventually resulted in the galaxies and stars we see today.

"We were waiting for the other shoe to drop, and this is it," says Andrew Lange, U.S. team leader and a professor of physics at Caltech. Lange was one of a group of cosmologists revealing new results on the cosmic microwave background at the American Physical Society's spring meeting April 29. Other presenters included teams from the DASI and MAXIMA projects.

The new results are from a detailed analysis of high-resolution images obtained by BOOMERANG, which is an acronym for Balloon Observations of Millimetric Extragalactic Radiation and Geophysics. BOOMERANG is an extremely sensitive microwave telescope suspended from a balloon that circumnavigated the Antarctic in late 1998. The balloon carried the telescope at an altitude of almost 37 kilometers (120,000 feet) for 10 and one-half days.

"The key to BOOMERANG's ability to obtain these new images is the marriage of a powerful new detector technology developed at Caltech and the Jet Propulsion Lab with the superb microwave telescope and cryogenic systems developed in Italy at ENEA, IROE/CNR, and La Sapienza," Lange says.

The images were published just one year ago, and the Lange team at the time reported that the results showed the most precise measurements to date of the geometry of space-time. The initial analysis revealed that the single detectable peak represented about a 1-degree expanse, which is precisely the size of large detail predicted by theorists if space-time is indeed flat. Larger peaks would have indicated that the universe is "closed" like a ball, doomed to eventually collapse in on itself, while smaller peaks would have indicated that the universe is "open," or shaped like a saddle, and would expand forever.

Cosmologists believe that the universe was created approximately 12 to 15 billion years ago in an enormous explosion called the Big Bang. The intense heat that filled the embryonic universe is still detectable today as a faint glow of microwave radiation that is visible in all directions. This radiation is known as the cosmic microwave background (CMB). Whatever structures were present in the very early universe would leave their mark imprinted as a very faint pattern of variations in brightness in the CMB.

The CMB was first discovered by a ground-based radio telescope in 1965. Within a few years, Russian and American theorists had independently predicted that the size and amplitude of structures that formed in the early universe would form what mathematicians call a "harmonic series" of structure imprinted on the CMB. Just as the difference in harmonic content allows us to distinguish between a piano and a trumpet playing the same note, so the details of the harmonic content imprinted in the CMB allow us to understand the detailed nature of the universe.

Detection of the predicted features was well beyond the technology available at the time. It was not until 1991 that NASA's COBE (Cosmic Background Explorer) satellite discovered the first evidence for structures of any sort in the CMB.

The BOOMERANG images are the first to bring the CMB into sharp focus. The images reveal hundreds of complex regions that are visible as tiny variations—typically only 100 millionths of a degree (0.0001 C)—in the temperature of the CMB. The new results, released today, show the first evidence for a harmonic series of angular scales on which structure is most pronounced.

The images obtained cover about 3 percent of the sky, generating so much data that new methods had to be invented before it could be thoroughly analyzed. The new analysis provides the most precise measurement to date of several of the parameters which cosmologists use to describe the universe.

The BOOMERANG team plans another campaign to the Antarctic in the near future, this time to map even fainter images encoded in the polarization of the CMB. Though extremely difficult, the scientific payoff of such measurements "promises to be enormous," maintains the U.S team leader of the new effort, John Ruhl, of the University of California at Santa Barbara. "By imaging the polarization, we may be able to look right back to the inflationary epoch itself—right back to the very beginning of time."

Data from the MAXIMA project is also being presented at the American Physical Society meeting, along with data from the CBI, which is also a National Science Foundation-supported mission. The CBI investigators, led by Caltech astronomy professor Tony Readhead, reported early results in the March 1 issue of the Astrophysical Journal. These results were in agreement with the finding of the other projects.

The 36 BOOMERANG team members come from 16 universities and organizations in Canada, Italy, the United Kingdom, and the United States. Primary support for BOOMERANG comes from the Italian Space Agency, Italian Antarctic Research Programme, and the University of Rome "La Sapienza" in Italy; from the Particle Physics and Astronomy Research Council in the United Kingdom; and from the National Science Foundation and NASA in the United States.

Contact: Robert Tindol (626) 395-3631