Magazine article Science News

Maps Sharpen View of Cosmic Radiation

Magazine article Science News

Maps Sharpen View of Cosmic Radiation

Article excerpt

Two new sky maps are giving astronomers their first direct glimpse of individual structures -- gravitational ripples -- in the primordial universe.

One of the new maps is a more accurate version of an earlier one that drew worldwide accolades when researchers presented it nearly two years ago. Based on the first year of data collected by NASA's Cosmic Background Explorer (COBE) satellite, this map showed tiny temperature fluctuations in the microwave background radiation believed left over from the explosive birth of the universe (SN: 5/2/92, p.292).

The pattern of hot and cold spots represents gravitational ripples in an otherwise smooth distribution of matter and energy in the infant universe. The ripples may have caused lumps to form there, ultimately creating clusters of galaxies. Though the overall pattern of hot and cold spots was statistically significant, the data contained about as much noise as signal. Thus, scientists could not identify any single feature as real.

Last week, at a meeting of the American Astronomical Society in Arlington, Va., the COBE team unveiled a new sky map based on an additional year of data. This distribution of hot and cold spots in the relic radiation has at least 1.4 times the amount of signal as noise, and some regions have about twice as much signal as noise, notes COBE researcher Charles L. Bennett of NASA's Goddard Space Flight Center in Greenbelt, Md. The added sensitivity means that some parts of the map probably show true structures in the microwave background, he says.

The new COBE-derived picture confirms that the tiny temperature variations were "not some fluke in the first year of data," Bennett says. Both maps show hot and cold spots that differ by 30 millionths of a kelvin from the 2.73-kelvin microwave background, but the new map halves the margin of error in this measurement. …

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