VERY LARGE ARRAY, N.M. (July 1) — Perhaps because the US will see a total solar eclipse next month, on August 21, for the first time in 38 years, interest in astronomy this year is strong, and so many visitors showed up for a guided walking tour at the Very Large Array near Socorro, New Mexico, one of two multi-antenna radio telescopes used by the National Radio Astronomy Observatory, that the 11 AM first-Saturday tour this morning had to be split into two separate groups.
And outdoors, where the facility’s 27 antennae operate from their vantage point on the high desert plains of New Mexico, that’s just fine: there’s plenty of room to walk around and spread out. But for the indoor portion of the tour, which included a visit to an engineer’s actual workbench as well as a five-minute question-and-answer session with the operations controller on duty, splitting it up like that meant the engineers were distracted twice as long.
See, even with tours going on—or, for example, when the Jodie Foster movie Contact was filmed in part on the site—the science doesn’t stop. Kristen, who was the operations controller on duty this morning, had her eyes glued to about six computer monitors while she was answering questions. One monitor notified her of any error conditions in the telescopes, one had up-to-the-minute weather reports and maps including any electrical storms in the area or the amount of humidity in the air, and another was a scheduler she could use to postpone or prioritize any research scripts that might work better under different environmental conditions.
The telescopes here operate 24/7, according to the tour guide, Judy. And for every hour of telescope time available, at least three different astronomical researchers ask for the time.
You might think that means two out of every three research requests get turned down, but it doesn’t really work that way in practice. What ends up happening, Judy said, is that a researcher might request one entire hour of telescope time but get only half an hour so that other research can be conducted in the unused half-hour.
The VLA is funded by your tax dollars, and researchers don’t pay any money to the federal government to use the telescopes. All they do is submit a proposal, and a team reviews each proposal and grants time on the telescopes to all the proposals that have merit.
One student asked Judy if the VLA ever actually discovered any evidence of E.T. Contrary to what the movie Contact would have us believe, she explained, the radio telescopes in the array aren’t really set up for that kind of work. “The best way to look for extraterrestrial life would be to scan large portions of the sky,” she said. The design of the array is such that it’s optimized for focusing on a single object in space. “But I’ll tell you what, if anybody ever did discover something unusual in the sky, like a signal from another world, the VLA would be the first group they would tell so we could point the telescope right at that source.”
Unlike optical telescopes, which show astronomers wavelengths in the 400–700 nm range, the radio telescopes pick up signals from electromagnetic radiation with a much longer wavelength, on the order of several meters or even kilometers. Each antenna actually has receivers for several different bands of radiation, and depending on which band a given researcher wants to study, different data are collected using a fiber optic network and a very fast computer.
The WIDAR, which stands for wideband interferometry digital architecture, has just one purpose: to correlate data received from all the telescopes, at the rate of about 16 quadrillion data points per second, and make sense out of it. A good analogy is perhaps the difference between a digital camera and an x-ray machine. Both take pictures of the human body, but an x ray doesn’t look anything like a JPG from a digital camera. The same goes for looking at stars with an optical telescope or a radio telescope: Both take pictures of the stars, but they don’t resemble each other and, while we can just see the data from an optical telescope, the data from a radio telescope requires significantly more computing power.
In fact, radio waves that the telescopes receive have so little energy that the combined total of energy processed by the VLA since its founding in the 1970s is less than the amount of energy a single snowflake transmits to the ground when it lands.
You might wonder why the telescopes are arranged in a “Y” configuration with four different diameters. Well, it turns out, there’s really nothing scientific about the “Y” arrangement. As far as data acquisition is concerned and the picking up of such low-energy signals, the telescopes would probably function as well if they were laid out randomly.
But, as a practical matter, each one of these 25-meter antennae weighs 230 tons and moving them is only possible on steel railroad tracks. Those tracks have to be laid in the ground and can’t be rearranged at the drop of a hat. Already, every time the observatory has to change the configuration of the antennae, which happens once every four months, the change can take several weeks. The research is still ongoing, since there are always at least 24 antennae receiving data, but it’s quite an operation to move a locomotive out to each antenna, which could be up to 13 km away, lift it up with hydraulics, move it to the new location, plug in the fiber optic cables, supercool the receivers, and so on.
It basically takes a village to get usable data out of the VLA, and those engineers and technicians who know about the cryogenic cooling don’t know how to steer the locomotive, the software programmers don’t know how to wire the circuit boards for the antennae, the operations controllers don’t really know what the communications department is doing with the various outreach or education programs, etc. The highly specialized knowledge each person possesses and brings to the job, out here basically in the middle of nowhere, an ideal place for a large radio telescope, is what keeps this team working to support important research.