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Out-of-this-world view of the Milky Way.

Out-of-this-world view of the Milky Way

Measurements of infrared radiation detected by an instrument aboard the Cosmic Background Explorer (COBE) spacecraft have allowed researchers to construct a unique portrait of the inner portion of the Milky Way.

"We see for the first time a very clear picture of our galaxy, with its nuclear bulge of stars," says Micahel G. Hauser of the NASA Goddard Space Flight Center in Greenbelt, Md. "This is what our galaxy looks like in starlight."

Astronomers have long pictured the Milky Way as a spiral galaxy -- a large, flattened disk of stars orbiting a common center. But direct, visual evidence for that view has been sparse. Although the sun traces an orbit near the fringes of the Milky Way, Earth-based observers have difficulty seeing through the dust that threads the galaxy's disk and surrounds its core. At visible wavelengths, they see only the relatively dust-free parts.

The new portrait of the Milky Way combines images obtained at three near-infrared wavelengths: 1.2 microns (represented in blue), 2.2 microns (green) and 3.4 microns (red). These wavelengths, slightly longer than those of visible light, correspond to radiation emitted mainly by stars rather than by dust particles, which absorb visible light and then reradiate that energy as infrared radiation. The image appears redder in directions where dust absorption is stronger. Images constructed previously from data obtained by the Infrared Astronomical Statellite revealed the sky's appearance at longer infrared wavelengths, where dust emissions play a much greater role.

The COBE-derived picture shows only that part of the galaxy closer to the galactic center than the sun, which orbits about 20,000 light-years out from the center. Discrete points that appear away from the Milky Way's central disk correspond to individual stars in the sun's immediate neighborhood.

"It's a spectacular image," says David T. Wilkinson of Princeton (N.J.) University. "It's almost as though you were in Andromeda [a nearby galaxy], taking a picture of our galaxy."

The new view is "one of the fringe benefits" of COBE program designed to provide a detailed infrared map of the sky, Hauser says. By looking for regions in the sky with the smallest possible infrared signal, investigators hope to find the fossil residue of light given off by the first luminous objects created after matter started to collapse into lumps early in the Universe's history. That search requires separating the faint, primordial infrared signal from the intense infrared sources now active within the galaxy and solar system (SN: 1/20/90, p.36).
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Author:Peterson, I.
Publication:Science News
Date:Apr 28, 1990
Words:422
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