For infrared astronomers, the air is as thick as pea soup, but three University of Rochester scientists, along with dozens of teams from around the world, are helping NASA clear the view. Rochester astronomers have completed crucial testing of two of the camera "eyes" on NASA's new infrared telescope to be launched into space. The camera will be placed into the telescope housing in Boulder, Colo., where engineers will make sure the detectors can perform in the frozen vacuum of space. The Space InfraRed Telescope Facility (SIRTF) will lift off from Cape Canaveral on Dec. 14, 2001, carrying aloft nearly two decades of work by the University team and other scientists from around the nation.
The $458 million instrument will provide the clearest view ever of the universe in infrared light-a wavelength of light that is invisible to the naked eye as well as most telescopes. Even specially built telescopes have a difficult time seeing infrared objects in space since Earth's atmosphere blocks most infrared light, leaving astronomers blind to regions of space that may actually be teeming with celestial objects. The ignition of fledgling stars, the evolution of solar systems and activity within the most distant galaxies are among the events SIRTF is specially designed to witness.
"Ground telescopes may be a lot cheaper to operate, but if you want the best infrared images, you have to go to space," explains astronomer William Forrest. "Not only does the atmosphere block infrared light but the Earth itself is glowing with it. It's like trying to look through a telescope that's lined with light bulbs."
Forrest and astronomer Judith Pipher were the first U.S. astronomers to turn an infrared array toward the skies, putting the University on the map as home to one of the world's strongest programs in infrared astronomy. At first Pipher built several single-pixel detectors, but using such detectors was like watching the skies through a pinhole. Pipher wanted more-a chip with hundreds or thousands of detectors-and her wish came true through a former Rochester scientist named Alan Hoffman who joined the aerospace company now called Raytheon. "When Alan left, he asked if he could send me anything, and as a joke I said, 'Sure, send me an array,'" Pipher says. A few years later, an infrared array with more than a thousand detectors was in her hands.
The array was originally designed to help the U.S. military see in the dark, but by 1983, Pipher and Forrest had turned it to more scientific aims and mounted it to the University telescope. In the small observatory on top of the Wilmot Building on campus, they took the first telescopic infrared pictures of the moon.
"It was a first-of-its-kind instrument and it was working immediately. We're very proud of that," says Pipher.
In that same year, NASA sent out word that it was looking for scientists to help build an infrared space telescope, and Pipher and Forrest put forth their ideas based in part on the infrared technology christened on campus. The proposal impressed NASA, and within just a few months Pipher and Forrest were evaluating and testing SIRTF's would-be eyes, and they were soon joined by Dan Watson, a newly hired astronomer. The Rochester contingent is part of a nationwide team of scientists from more than a dozen academic institutions and aerospace companies; the project is led by the SIRTF Science Center at the Caltech-NASA Jet Propulsion Laboratory in Pasadena, Calif.
For more than a decade now, Pipher, Forrest and Watson, professors in the Department of Physics and Astronomy, have been working toward SIRTF's 2001 launch date. The team, along with engineers and students at the University, has been testing the detector arrays that were created at Raytheon, looking to squeeze every last bit of sensitivity out of them. When a detector arrives at the University, one of the researchers places it inside a dewar-a sort of ultra-cool thermos-and chills it down to minus 432 degrees Fahrenheit. There the researcher aims the "eye" at a variety of cold objects to determine if the array is seeing an image properly, if it's causing any kind of interference with itself, and what ways of using the particular array might provide the best results. With what they learn in the evaluations, the team makes recommendations to Raytheon on how to enhance performance or decides when an array is good enough to go into space.
The SIRTF arrays pack more than 65,000 detectors into a space no bigger than a fingernail. Every one of those detectors must be able to react to the slightest bit of infrared light from a distant galaxy while frozen in space, floating in a vacuum, and under bombardment by cosmic rays-and do it all far beyond the reach of any shuttle repair mission. The members of the team are confident that their arrays will allow SIRTF to see thousands more and fainter objects than any infrared telescope to date. The arrays are central to SIRTF's infrared camera, one of three instruments aboard the solar-powered, 1,600-pound craft. Forrest and Watson have also helped design the craft's spectrograph, a device that can tell what a star or planet is made of just by analyzing the light from it. On board will also be a photometer to measure the brightness of objects.
Once above the atmosphere, SIRTF will be in its element. Just as the Earth's atmosphere blocks most infrared light, great clouds of cosmic dust block out most visible light long before it ever gets to Earth, so even space telescopes like the Hubble can have trouble getting a good view. But infrared light passes through cosmic dust with ease, letting scientists see past it to ancient galaxies or stellar nurseries. There, astronomers can witness new stars igniting for the first time, or whole worlds forming from the surrounding rings of dust. Once SIRTF is in orbit around the sun, one-fifth of its observing time will be reserved for the scientists who have designed and built it, assuring the Rochester group many weeks to study these and other phenomena.
"I'm looking forward to the hunt for brown dwarfs," says Pipher. Brown dwarfs are massive planet-like objects that were too small to start fusion and become stars. Brown dwarfs radiate almost no visible light (hence "brown") but do shine brightly at the infrared end of the spectrum. They're theorized to make up much of the "dark matter" that permeates the universe; the mysterious material may be ten times more prevalent than the stars we see.
Pipher, Forrest and Watson are also working on detector arrays for NASA's Next Generation Space Telescope (NGST), which is planned to be much like the Hubble, but with the ability to explore both infrared and visible wavelengths.