Spitzer Space Telescope detects organic molecules in a bright galaxy

By David Brand and Blaine P. Friedlander Jr.

Borrowing a page from the Superman legend, astronomers have used the infrared vision of an orbiting telescope to penetrate the universe's obscuring dark mass and bring it into cosmic clarity.

Houck

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., 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 in 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.

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), the same structure teems with physical and chemical activity. NASA/JPL/Caltech

The IRS is the most sensitive infrared spectrograph ever to go into space. In less than 15 minutes, Houck said, 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 said. (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, said Houck.

"What we are seeing is the merger of two galaxies," he said. "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 said, 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 conceded. "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," Houck said during the Dec. 18 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.

Said Houck, "It was a staggering event."