The Why Files The Why Files --

Astronomy in Orbit

Seeing heat
Visible light is not the only type of electromagnetic signal coming from stars and galaxies. In the past few years, orbiting telescopes that read X-rays, ultraviolet and infrared light have been launched. Spitzer Space Telescope, named for Lyman Spitzer, Jr., the astronomer who first suggested putting giant telescopes in space, reads infrared, the kind of radiation given off by cool objects, like dust.

Illustration of Spitzer Space Telescope.Spitzer Space Telescope, launched in August, 2003, is designed to work for at least two-and-a-half years. To collect infrared light without distortion, the 85-centimeter beryllium mirror is cooled by liquid helium to less than 5.5 degrees C above absolute zero. Here, an artist's rendition shows NASA's Spitzer in front of an infrared view of the Milky Way galaxy. Illustration: NASA

Spitzer can look at:
Brown dwarfs: These "failed stars," between Jupiter and the sun in mass, are hard to see, but they may be extremely common.

Circumstellar disks: The whirling gas and dust surrounding stars carries hints about the early universe.

Clouds of hydrogen: These giant clouds, which can coalesce into stars, give off no visible light, but plenty of infrared

Seeing the invisible
To see what your eyes are missing, compare the visible-light picture of the Trifid Nebula to the false-color infrared views. The Trifid Nebula is a giant cloud of gas and dust 5,400 light-years distant. While dusty regions in the visible-light image suggest locations where stars might be forming, the infrared image allows astronomers to actually count star embryos: 30 massive embryonic stars a-borning, and 120 smaller newbies. Ten of the big embryos appear in four dark cores called stellar "incubators."

 Four views of stars seen in different wavelengths
The Trifid Nebula in visible and infrared views. Infrared shows intense star formation where visible light shows only heavy dust.
Left: Visible light, from National Optical Astronomy Observatory
Middle: Composite Spitzer infrared image
Top right: Spitzer's infrared array camera reads light at 4.5 microns (blue), 8.0 microns (green) and 24 microns (red).
Bottom right: Multiband imaging photometer, at 24 microns, shows cool material falling onto star embryos.
Photos: NASA/JPL-Caltech/J.Rho(SSC/Caltech)

The driving force in this nebula is a gargantuan explosion of a massive "type O" star (the remains are that faint white spot at the center). Type O's, the most massive stars, live fast and die young, in an explosive supernova.

See the Spitzer slide show.

What can you learn from X-rays?

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Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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