CCAT Takes the Torch
A rough road switchbacks up the flanks of Cerro Chajnantor in Chile's Atacama Desert and levels out on a small plateau 80 feet below the summit. If you stood on that plateau, 18,500 feet above sea level in the driest desert on Earth, you might first notice the absence of life—no plants rustle in the wind, no lizards dart among the rocks. Below, golden desert stretches between the coastal mountains and the Andes, isolated by their rain shadows from both ocean storms and humid gusts from the Amazon Basin. The great plain has no correspondingly great river, the peaks no glaciers, and the air almost no moisture. If you set a glass on the dirt and condensed all the water vapor in the air above the glass into it, the collected water would stand at less than a millimeter. With its thin, parched atmosphere, this is the premier location for CCAT, a planned submillimeter-wavelength observatory that goes by the working title of Cerro Chajnantor Atacama Telescope. According to CCAT deputy project manager Simon Radford, our view of the submillimeter sky, which is limited by atmospheric water vapor, is better here than anywhere except Antarctica and space, where construction and upgrades would cost a bit more.
When the veil of water vapor is lifted, the universe is as bright at submillimeter wavelengths as it is in visible and ultraviolet light combined. Clouds of gas and dust that appear dark to our eyes and to optical telescopes shine in submillimeter light, revealing massive stellar nurseries and hidden galaxies.
Nobel laureate in physics Robert Wilson, PhD '62, who chaired the observatory's technical review committee, predicts that CCAT "will revolutionize astronomy" in the submillimeter and far-infrared band and "enable significant progress in unraveling the cosmic origins of stars, planets, and galaxies." He emphasizes, "CCAT is very timely and cannot wait."
CCAT will succeed the legendary Caltech Submillimeter Observatory on Mauna Kea, which captured its first data in 1987. (See E&S Summer 1988.) When CCAT's eye opens in 2016, the CSO's eye will close. "The timing of this works very nicely," says Tom Phillips, CSO's director and the Altair Professor of Physics. "The international community of astronomers that relies on the CSO will have a seamless transition as CCAT comes online." After a good solid party in the CSO's honor, the telescope's site will be returned to nature. Though the site may appear as it once did, the universe never will.
The CSO was the brainchild of Robert Leighton (BS '41, MS '44, PhD '47), a physicist fascinated with underexplored wavelengths who taught at Caltech until his retirement in 1985 and often spent evenings building balsa-wood telescope models in his garage. Equipped with a 10.4-meter Leighton Dish and a state-of-the-art single-pixel receiver invented by Phillips, the CSO helped astronomers gain insight into the chemistry of space, the birth of nearby galaxies and stars, the composition of comets and planets, and the origins of terrestrial water. Designed for upgradability, the CSO also enabled tests of new detectors.
CCAT will see a broader wavelength range—from 200 micrometers to 2.2 millimeters—using the latest detectors. While the CSO started off with a single-pixel receiver, CCAT will sport two 50-kilopixel cameras based on Microwave Kinetic Inductance Detectors, or MKIDs. Invented by Jonas Zmuidzinas (BS '81), professor of physics and director of JPL's microdevices laboratory, along with JPL Senior Research Scientist Henry "Rick" LeDuc, MKIDs are superconducting photon detectors that are cheaper to fabricate and easier to assemble into large arrays than transition edge sensors, the competing technology. MKID arrays are also considered more likely to be scalable into megapixel cameras, for which CCAT's designers have thoughtfully left room. But MKIDs are relatively new. Zmuidzinas began working on them in 2000 with seed funding from Trustee Alex Lidow, BS '75, and the first prototype camera was installed on the CSO in 2007.
CCAT's dish, 2.5 times bigger and nearly twice as smooth as the CSO's, will gather more light and focus more sharply. David Woody, a key contributor to many Caltech telescope projects, is honing the design of the primary mirror and its support, in which some 1,800 reflector tiles premounted in groups on 200 "rafts" are secured to a carbon-fiber truss. A network of sensors and actuators will keep the surface smooth to within ten micrometers—between the width of a red blood cell and a white blood cell. "CCAT is a really tough technical challenge," says lead telescope designer Steve Padin, whose work with Woody is supported by a five-year gift from John B. and Nelly Kilroy.
Astronomers will use CCAT to test the prevailing wisdom about the evolution of galaxies, stars, and black holes. Here's the gist of the story. After the Big Bang, the universe—most of which is dark matter—varied slightly in density. Over billions of years, gravity emptied material from less dense areas into denser ones, which, in turn, merged into larger structures. As the dense regions merged, galaxies that had coalesced inside of them also gravitated toward each other, often colliding and merging. These smash-ups roiled the gas clouds within the galaxies, triggering bursts of star formation and causing much of the gas to sink toward the merged galaxies' cores, fueling the growth of supermasssive black holes.
Everything we can see fits this story, but the problem is that, at most wavelengths, the picture dims at the height of the action. In the universe's first few billion years, when all those galactic collisions and mergers were making new stars hand over fist, those stars were born enshrouded by gas and dust, making them invisible. But the copious ultraviolet light from the new stars heated that dust, which reradiated the heat at longer wavelengths that penetrate the dust and are visible to CCAT, enabling astronomers to tell what happened behind the curtain.
Recent submillimeter observations have turned up hundreds of distant galaxies that give off most of their light in the submillimeter and far-infrared bands. These are the ancient, colliding galaxies that astronomers want to see. Big, fast, and sensitive, CCAT will find hundreds of thousands of such objects. CCAT will survey the submillimeter sky from the earliest era of galaxy formation forward, measuring luminosity, redshift, and color.
Astronomers will sift through this wealth of newly discovered galaxies for those with the most potential to refine the story, and will follow up with closer observations at narrowly focused instruments like the Thirty-Meter Telescope and the Atacama Large Millimeter/Submillimeter Array (ALMA), an interferometer under construction on a plateau 2,000 feet below CCAT.
At the other end of the cosmological scale, CCAT will turn its dust-vision on our own sun's remnant disk—the Kuiper Belt beyond Neptune—to catalog and analyze hundreds of objects dating back to the birth of our solar system. This and CCAT studies of other stellar disks, from protoplanetary systems to old debris, will offer new insights into how planetary systems form.
As planning for CCAT advances, the community of interested astronomers swells. CCAT, initially the Cornell Caltech Atacama Telescope, got its new working title in recognition of the consortia of British, German, and Canadian astronomers, plus American partners, including the University of Colorado and Associated Universities Inc., that have signed on.
"The worldwide community is excited about CCAT, and there is no shortage of potential partners. It is wonderful for Caltech and JPL to be in the position of playing a leading role in the development of this unique and powerful new telescope," says Andrew Lange, Goldberger Professor of Physics, who has made CCAT the Division of Physics, Mathematics and Astronomy's number-one priority since becoming division chair one year ago. —AW