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In the far-infrared, stars are not especially bright, but we can see emission from very cold matter (140 Kelvins or less) that 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. This is due to thermal radiation of interstellar dust contained in molecular clouds. 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: These emissions are from dust in circumstellar shells around numerous old red giant stars. These stars heat up the dust and cause it to glow brightly in the infrared. The Bolocam Galactic Plane Survey mapped the galaxy for the first time in the far-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 82. 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. Many galaxies ("active 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, the Caltech Submillimeter Observatory, and the Submillimeter Array. Most far-infrared astronomy is performed by satellites such as the Herschel Space Observatory, Spitzer, IRAS, and ISO. Upper-atmosphere observations are also possible, as conducted by the airborne SOFIA telescope.
- "Near, Mid and Far-Infrared". Caltech Infrared Processing and Analysis Center. Retrieved 2013-01-28.
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