Paula Cleggett-Haleim Headquarters, Washington, D.C. April 23, 1992 (Phone: 202/453-1547) 12:00 p.m., EDT Randee Exler Goddard Space Flight Center, Greenbelt, Md. (Phone: 301/286-7277) RELEASE: 92-52 COBE DETECTS STRUCTURE OF EARLY UNIVERSE Scientists announced today, at the American Physical Society's meeting held in Washington, D.C., that they have detected the long-sought variations within the glow from the Big Bang -- the primeval explosion that began the Universe 15 billion years ago -- using NASA's Cosmic Background Explorer (COBE). This detection is a major milestone in a 25-year search and supports theories explaining how the initial expansion happened. These variations show up as temperature fluctuations in the sky, revealed by statistical analysis of maps made by the Differential Microwave Radiometers (DMR) on the COBE satellite. The fluctuations are extremely faint, only about thirty millionths of a degree warmer or cooler than the rest of the sky, which is itself very cold -- only 2.73 degrees above absolute zero. The DMR is still gathering data and the measurements are expected to become even more precise. The Big Bang theory was initially suggested because it explains why distant galaxies are receding from us at enormous speeds, as though all galaxies started moving away from the same location a long time ago. The theory also predicts the existence of cosmic background radiation -- the glow left over from the explosion itself. The Big Bang theory received its strongest confirmation when this radiation was discovered in 1964 by Arno Penzias and Robert Wilson, who later won the Nobel Prize for this discovery. Although the Big Bang theory is widely accepted, there have been several unresolved mysteries. How could all of the matter and energy in the Universe become so evenly mixed in the instant following the Big Bang? How could this evenly distributed matter then break up spontaneously into objects of all sizes, such as galaxies and clusters of galaxies? The temperature variations seen by COBE help to resolve these mysteries. - more - - 2 - "The COBE receivers mapped the sky as it would appear if our eyes could see microwaves at the wavelengths 3.3, 5.7 and 9.6 mm, which is about 10,000 times longer than the wavelength of ordinary light," explained Dr. George Smoot, University of California, Berkeley, the leader of the team that made this discovery. "Most of the energy received from the sky at these wavelengths is from the cosmic background radiation of the Big Bang, but it is extremely faint by human standards. "Hundreds of millions of measurements were made by the DMR over the course of a year, and then combined to make pictures of the sky. Making sure all the measurements were combined correctly required exquisitely careful computer analysis," Smoot explained. Another COBE scientist, Dr. Charles Bennett of the Goddard Space Flight Center, Greenbelt, Md., explained that a major challenge for the team was to distinguish the Big Bang signals from those coming from our own Milky Way Galaxy. "The Milky Way emits microwaves that appear mostly concentrated in a narrow zone around the sky. We compared the signals at different positions and at different wavelengths to separate the radiation of the Big Bang from that of the Milky Way Galaxy," said Dr. Bennett. The temperatures and sizes of the fluctuations in the background radiation COBE detected agree with the predictions of "inflationary cosmology," a theory that says the structure and behavior of the Universe were determined by minute fluctuations occurring when the Universe was much younger than one-trillionth of a second. The COBE results provide new evidence in support of the "inflationary" scenario. The amount of gravity provided by these visible fluctuations was inadequate to draw together the galaxies and clusters of galaxies. Instead, astronomers conclude that the galaxies formed only because most of the material in the Universe is invisible and totally unlike ordinary matter. This "dark matter" provides the necessary gravitational attraction for forming galaxies. The fluctuations seen by COBE are too small to explain how the visible matter in the young Universe could condense into the galaxies that now exist. According to COBE scientist Dr. Edward Wright from the University of California, Los Angeles, the COBE measurements support theories postulating large amounts of dark matter. "These theories say that most of the matter in the Universe is invisible to us and must be a new kind of matter, not yet detected in our laboratories," he explained. "Nevertheless, we need such invisible matter to explain how galaxies formed in the early Universe and gathered themselves together into huge clusters. Ordinary matter would be attracted into regions of concentrated dark matter, and the Universe as we know it today could develop, eventually leading to the formation of galaxies, stars and planets," Wright said. - end -