Orbiting observatory detects organic chemistry in one of the most luminous galaxies ever found

by David Brand and Blaine Friedlander Jr.

Above, side-by-side images show the stark contrast between the visible light and the infrared parts of the electromagnetic spectrum. On the left, the constellation Orion is shown in the optical part of the spectrum. The right side depicts Orion in the infrared. Below, viewing a large cosmic structure called Herbig-Haro 46/47, optical telescopes could detect only the opaque mask (inset). In the infrared (the larger image) that same structure teems with physical and chemical activity. NASA/JPL

The last of NASA's Great Observatories, newly named the Spitzer Space Telescope, has found evidence of organic molecules in one of the brightest galaxies ever detected, said James Houck, Cornell professor of astronomy, speaking at a NASA press conference at the space agency's headquarters in Washington, D.C., on Dec. 18.

"In the infrared, this is really a boomer," said Houck, explaining that the galactic light likely originated 3.25 billion years ago, when life first became prevalent on Earth. He estimated the galaxy's luminosity as 10 trillion times the brightness of the sun -- "that's a huge number even in this town."

Houck is principal investigator for the infrared spectrograph (IRS), one of the three instruments on the observatory (previously called the Space Infrared Telescope Facility, or SIRTF).

Manager of the mission for NASA is the Jet Propulsion Laboratory, Pasadena, Calif., a division of the California Institute of Technology.

Lyman Spitzer (1914-1997), for whom the telescope is named, was a Princeton astronomer who examined interstellar matter, star clusters and plasma physics. He first suggested a space telescope in 1946.

Also released at the NASA press conference were dazzling images taken with the space telescope's infrared-array camera and with its multiband-imaging photometer. The images include a glowing stellar nursery; a swirling, dusty galaxy; a disc of planet-forming debris; and organic material in the distant universe.

The IRS is the most sensitive infrared spectrograph ever to go into space. In less than 15 minutes, Houck says, it produced a spectrum of the distant galaxy IRAS 00183, first observed by the infrared astronomical satellite (IRAS) in 1983.

The spectrum "gives evidence for organic chemistry in a distant galaxy shortly after the formation of the Earth," he says. (While the Spitzer observatory's cameras take infrared snapshots of distant galaxies and dust clouds, and objects too cool to emit visible light, the IRS determines their precise infrared colors. Astronomers are then able to read the peaks and valleys in the spectrum, called emission and absorption lines, to determine the chemical mix of the object being observed.)

In an optical image, the IRAS galaxy appears as no more than a faint smudge. But the IRS spectrum -- the first detailed look at the galaxy -- shows a broad silicate feature. The dominant absorber of visible energy is tiny silicate dust particles. The silicate dust is so opaque that only a small percentage of the visible light escapes the galaxy, says Houck.

Jim HouckCopyright © Cornell University Click on the image for a high-resolution version (774K)

"What we are seeing is the merger of two galaxies," says Houck. "Either what we are seeing is a brief flash of incredibly strong star formation, or one or both of the galaxies contained a black hole before colliding. The massive black holes are releasing the energy by swallowing stars and gas." In both cases, he says, the collision would compress gas that would trigger the star formation or the release of energy from the black hole, a process called "feeding the monster." Both scenarios have problems, Houck concedes. "One is, how do you get enough gas close enough to a black hole to make all this happen? And how do you get stars to form so quickly all at the same time?"

The spectrograph team also released an image of HH46IR, a "dusty, dirty cloud" in our galaxy, the Milky Way, that visible light is unable to penetrate. The spectrum shows the cloud to be a region of star formation containing organic materials, including methyl alcohol, carbon dioxide ice and carbon monoxide gas and ice. "It's a poisonous place," he told the press conference.

Spitzer Space Telescope scientists believe the minimum life span for the observatory is about five years, when its liquid helium coolant (at a frigid minus 450 Fahrenheit) is expected to run out. The telescope already has faced one challenge: In November, the spectrograph was subjected to a massive proton "storm" in space, with 1.6 billion atomic particles (mostly protons) bombarding a square centimeter of the instrument in just two days. Says Houck: "It was a staggering event."

Related World Wide Web sites: The following sites provide additional information on this news release. Some might not be part of the Cornell University community, and Cornell has no control over their content or availability.

o Spitzer Space Telescope/JPL: <http://sirtf.caltech.edu/ >

o Cornell News Service reports on Spitzer/IRS:

http://www.news.cornell.edu/releases/SIRTF/

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