14. Seeing the Cosmos in Infrared Spectra

James R. Houck, Astronomy, and his SIRTF team designed the most sensitive infrared spectrograph (IRS) ever to go into space. Its job is to penetrate the coldest and dirtiest parts of the cosmos and uncover the composition of distant stars and interstellar gas. It detects infrared radiation, which cannot be observed from the ground because of Earth’s atmosphere. The IRS is aboard NASA’s orbiting infrared observatory, newly named Spitzer Space Telescope (previously called the Space Infrared Telescope Facility, or SIRTF), launched on August 25, 2003. The Spitzer observatory cameras take infrared snapshots of distant galaxies and dust clouds, and objects too cool to emit visible light, and the IRS determines their precise infrared colors. Scientists read the peaks and valleys in the spectrum, called emission and absorption lines, to determine the chemical mix of the object under observation.

Among the first reports from the Spitzer observatory was engrossing news: the IRS found evidence of organic molecules in one of the most luminous galaxies ever, IRAS 00183 (first observed by infrared astronomical satellite in 1983). The galaxy is 3.25 billion light years from Earth, equaling 10 trillion times the luminosity of the sun. Houck described the event as the merger of two galaxies, which produced a brief flash of extremely strong star formation, or one or both of the galaxies contained a black hole before colliding. The massive black holes are releasing energy by swallowing stars and gas. Houck questioned: How is there enough gas close enough to a black hole to make all this happen? How do stars form so quickly all at the same time?

Houck’s team also released a spectrum of HH46IR, a dusty, dirty cloud in our Milky Way galaxy, which visible light is unable to penetrate. The spectrum showed the clouds to be a region of star formation containing organic materials, including methyl alcohol, carbon dioxide ice, and carbon monoxide gas and ice.

Houck heads the scientific team on the $39 million IRS contract with the Jet Propulsion Laboratory, a division of the California Institute of Technology, manager of the mission for NASA.

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