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Mapping Big Bang's Shadow

Scientists hope that MAP satellite will be able to report on the content and expansion of the universe. Results will take months.


Gazing at the night sky, it's easy to become overwhelmed by the immensity of the universe. What's out there? What does it all mean? NASA scientists have not undertaken to answer the riddles of the meaning of life, but they hope a satellite they launched recently will give clues to the earliest events in the universe.

The satellite, called MAP for Microwave Anisotropy Probe, will examine the afterglow of the formation of the universe. Scientists hope the examination will help answer questions about what the universe is made of and how quickly it is expanding.

In particular, they think the MAP project may be able to determine once and for all whether exotic "dark matter" and "dark energy" exist, how much of the universe they make up, and just what their nature might be.

MAP, launched June 30, will examine what astronomers call the cosmic background radiation--the leftover glow from the Big Bang that physicists hypothesize was the dawn of the universe. The light is a "fossil relic of ancient times," says Dr. Chuck Bennett, an astrophysicist at NASA's Goddard Space Flight Center and principal investigator for the mission.

The radiation has its origin only 300,000 years after the beginning of the universe, and the images produced by MAP will provide a detailed picture of the universe as it existed then. In the intervening billions of years, when the light has traveled trillions of kilometers, the radiation has cooled to just a few degrees above absolute zero (-460 degrees). But even in this much cooler state, the radiation preserves the pattern of the universe in its infancy.

According to prevailing physics theories, which have been strongly supported by experimental evidence, the universe suddenly came to be from nothing and has been growing ever since. The theories hold that, in the microseconds after it began, the universe underwent an unimaginably rapid and sudden expansion, growing by billions of times in size in a fraction of a second.

Expansion of the universe was remarkably uniform, resulting in an almost-even distribution across the entire universe. But had the distribution been totally smooth, there would be no galaxies or planets or people, just an evenly spread sea of stuff.

Instead, when we look to the heavens we see "a clumpy-looking sky"--clumps made of stars, of galaxies, of clusters of galaxies, explains Bennett. These clumps probably grew from "seeds," or tiny spots in the earliest universe where matter was more concentrated than at other spots.

Those spots, in turn, are mirrored in the background radiation as tiny fluctuations in the temperature of the remaining glow.

Those temperature differences are so tiny--only millionths of a degree--that the hunt for their existence went on for 27 years. In 1992, a satellite called COBE (Cosmic Background Explorer) brought back the first hard evidence of the variations.

Now, researchers hope MAP will provide detailed images of the fluctuations across the universe. Having a detailed map of the temperature variations should help scientists develop a picture of what the infant universe looked like. Scientists also hope the MAP data will help them figure out the puzzle of the so-called dark matter that they believe makes up the vast majority of the contents of the universe.

All the ordinary matter in the universe--the stuff that makes up everything we can see, from dust to stars--does not add up to enough to generate the gravitational force that holds the universe together. To account for the gap--to explain why the universe has not simply flown apart over billions of years--scientists have hypothesized the existence of what has been called "dark matter"--because it does not interact with light and thus cannot be seen--as well as an even more elusive dark energy.

By studying the cosmic radiation, the MAP team hopes to learn about dark matter by seeing how it interacted with the cosmic radiation.

The tiny size of the temperature differentials within the radiation--billions of times smaller than the contaminating light from the sun, Earth and moon--pose the greatest challenge for MAP's designers. The key, as the real estate saying goes, is location, location, location.

In this case, the ideal location is a place called L2--an orbital position about four times farther from the Earth than the moon is, heading away from the sun. Satellites studying the sun are often parked in the opposite direction, known as L1; MAP will be the first satellite to orbit at L2.

One advantage of L2 is that the distance from the sun makes it somewhat easier to detect the tiny fluctuations in temperature within the background radiation.

In addition, MAP will be able to gather data from 100% of the sky. Other ground and balloon-borne efforts have given high-resolution data, but for only 1% to 2% of the sky.

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