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Far infrared astronomy
In the far-infrared, stars are not especially bright, but we can see emission from very cold matter (140 Kelvin or less) which is not seen at shorter wavelengths.
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 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.
Except for the plane of our own galaxy, the brightest far-infrared object in the sky is central region of a galaxy called Messier object 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.
The Earth's atmosphere is opaque over most of the far infrared, so that ground-based observations are limited to submillimetre wavelengths using high altitude telescopes such as the James Clerk Maxwell Telescope. Most far-infrared astronomy is performed by satellites such as Spitzer, IRAS and ISO. Future missions will include the Herschel Space Observatory and the airborne SOFIA telescope.
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