CARMA is the Combined Array for Research in Millimeter-wave Astronomy. It’s a collection of 23 small- to medium-size radio telescopes at the south end of the White Mountains, in a pretty remote part of Inyo County, California (map). Every year, on a Saturday in early June, the good people there host an open house so that curious folks like me can come learn about their mind-bending astronomical research. And see their amazing technology up close. And enjoy a hot dog lunch in the shade.
CARMA is at Cedar Flat, just off State Route 168, near Westgard Pass, at 7,200 feet. It’s an “array” because several antennas look at the same object at the same time, creating images far more detailed than any one antenna could create on its own. It’s a “combined” array, because it includes six 10.4-meter antennas that previously lived in nearby Owens Valley, nine 6.1-meter antennas previously installed at Hat Creek in northern California, and eight additional 3.5-meter antennas.
First stop: a tour of the observing and signal processing facilities. This is the Correlator Room, where radio signals from distant stars and galaxies, collected by several antennas, are combined and processed to pull a very faint signal out from a lot of loud noise (think of extracting a faintly whispered message from the loudest static between stations on the AM radio dial).
They use radio waves as short as a millimeter to measure the speeds, masses, and composition of objects within our own solar system and on the farthest detectable edges of the universe. From this, they decipher the evolution and properties of everything we see in the sky. Somehow, they make it sound almost easy.
Here’s one of the 10.4-meter (diameter) antennas.
Radio telescopes have mirrors, too. They don’t need to be as smooth and shiny as the mirrors in optical telescopes, but they are highly reflective for radio waves just a millimeter or two in length. The first mirror is the big dish; the second mirror sits on a tripod above the middle of the dish and focuses the signal toward the diagonal plate in the middle of the picture above. This third mirror reflects the signal through the opening at left, toward the actual antenna. The antenna itself is only about as long as the wavelengths it is collecting: a few millimeters or less. And it’s cooled with liquid helium to an incredible 4 degrees Kelvin (that’s minus 452 degrees Fahrenheit) to avoid adding more noise to an already faint signal.
A group of 6.1-meter antennas.
A squad of 3.5-meter antennas.
The antennas in the array are moved into different configurations several times a year to enable different kinds of astronomical viewing and in response to seasonal changes in atmospheric conditions. Generally, the antennas are closer together in summer and farther apart in winter. But how do you pick up a delicate radio telescope weighing many tons? You use the custom-built transporter, above, designed by the man standing at its center. And you move it, slowly, with the 6-wheel drive Oshkosh behemoth pictured below.
Check out CARMA’s web site for pictures of what they look at with their instruments!
Tim Messick Photography • Graphics
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