Monday, March 16, 2009


IRAS view of infrared cirrus - dust heated by starlight

In the far-infrared, the stars have all vanished. Instead we now see very cold matter (140 Kelvin or less). Huge, cold clouds of gas and dust in our own galaxy, as well as in nearby galaxies, glow in far-infrared light. In some of these clouds, new stars are just beginning to form. Far-infrared observations can detect these protostars long before they "turn on" visibly by sensing the heat they radiate as they contract."

the COBE/DIRBE Science Team, and NASA<br />
Michael Hauser (Space Telescope Science Institute),
the COBE/DIRBE Science Team, and NASA

The center of our galaxy also shines brightly in the far-infrared because of the thick concentration of stars embedded in dense clouds of dust. These stars heat up the dust and cause it to glow brightly in the infrared. The image (at left) of our galaxy taken by the COBE satellite, is a composite of far-infrared wavelengths of 60, 100, and 240 microns.

IRAS infrared view of the Andromeda Galaxy
IRAS infrared view of the Andromeda Galaxy (M31) - notice the bright central region

Except for the plane of our own Galaxy, the brightest far-infrared object in the sky is central region of a galaxy called M82. The nucleus of M82 radiates as much energy in the far-infrared as all of the stars in our Galaxy combined. This far-infrared energy comes from dust heated by a source that is hidden from view. The central regions of most galaxies shine very brightly in the far-infrared. Several galaxies have active nuclei hidden in dense regions of dust. Others, called starburst galaxies, have an extremely high number of newly forming stars heating interstellar dust clouds. These galaxies, far outshine all others galaxies in the far-infrared.

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