COBE sky map

This map of the ancient sky shows the minute variations in the microwave background discovered by the team led by Lawrence Berkeley Laboratory astrophysicist George Smoot. As seen in the map, vast regions of space have minute variations in temperature. Over billions of years, gravity magnified these small differences into the clusters of galaxies we observe today. Displayed horizontally across the middle of the map is the Milky Way galaxy.

The image, a 360-degree map of the whole sky, shows the relic radiation from the Big Bang. The map was derived from one year of data taken by the Differential Microwave Radiometers onboard NASA's Cosmic Background Explorer satellite. Using Galactic coordinates, the map shows the plane of the Milky Way galaxy horizontally and the center of our galaxy at its center.

The colors represent temperature variations with red indicating regions that are a hundredth of a percent warmer and blue indicating regions that are a hundredth of a percent cooler than the average temperature of 2.7 degrees above absolute zero. Away from the plane of the galaxy, many of the features shown are noise.

According to the "inflationary Big Bang" theory on the birth of the universe, as the universe began to expand in the instant after the primeval explosion, its energy density was nearly uniform in all directions save for very small amplitude variations. Gravity working over billions of years magnified these variations, causing galaxies to form and to cluster in the sky. These galaxy clustering patterns, predicted by theory, have been seen for several years, but this study provides the first evidence for the corresponding fluctuations in the background radiation in the sky. Thus, a 15-billion-year-old fossil of the conditions of the universe has been detected and measured for the first time.

Computer analyses show that the pattern of the fluctuations agrees with the predictions from the inflationary Big Bang scenario. The amplitudes of the observed fluctuations are consistent with theories that explain the birth and growth of galaxies using large amounts of an enigmatic material called "dark matter." According to these theories, most of the universe is composed of material that we not only know very little about, but that has never been seen directly.

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