Date: February 6, 2010
Title: Expanding an Already Very Large Array
Podcaster: Nicole Gugliucci
Links: The Very Large Array – http://www.vla.nrao.edu
The NRAO Image Archive – http://images.nrao.edu
The EVLA – http://www.aoc.nrao.edu/evla
One Astronomer’s Noise – http://noisyastronomer.com/365-days-of-astronomy/
Music from Dorian Spencer: http://www.dorianspencer.com/
Description: One of the most productive telescopes in astronomy, the Very Large Array, has shut down its operations for the first two months of this year in order to give it a much anticipated upgrade. Find out more about what this new Expanded Very Large Array will have in store.
Bio: Nicole Gugliucci is a graduate student at the University of Virginia, working at the National Radio Astronomy Observatory. When not helping with the construction and data analysis for PAPER, she enjoys public outreach activities, especially those that allow her to talk about the fascinating discoveries to come out of radio astronomy.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Kylie Sturgess of the Token Skeptic podcast, investigating superstitions and the science behind them at www.tokenskeptic.org.
Hello and welcome to another edition of the 365 Days of Astronomy podcast. I’m Nicole Gugliucci, graduate student in astronomy at the University of Virginia and National Radio Astronomy Observatory in Charlottesville. You may know me online as the Noisy Astronomer. Today, we’re going to talk about the shut-down and rebirth of one of the most productive telescopes in astronomy… the Very Large Array.
Have you ever seen the movie “Contact?” You know, the one starring Jodie Foster and based on a wonderful book by Carl Sagan about what might happen if we make contact with an extraterrestrial intelligence? The ET signal in the movie is detected at the VLA, a Y-shaped radio interferometer located on the plains of San Augustine in New Mexico in the United States.
(And no, we don’t listen to radio signals… it’s actually a form of light. When turned into sound, most astronomical objects are just static. But anyway…)
Although the VLA is not involved in any ET searches, astronomers have used this telescope for decades to probe planets, star formation regions, interacting galaxies, powerful jets from active galaxies, and so much more. A quick search of the NASA Astrophysics Data System shows that 11499 papers have VLA or “Very Large Array” in the abstract going back to 1972, although the full array was not commissioned until 1980. This versatile instrument allows astronomers to observe at a number of different frequencies, or wavelengths, of radio light and with different spatial resolutions, as the 27 antennas are moved along railroad tracks to different distances from the center of the site.
(For the record, “Contact” was filmed while the array was in its most compact, and arguably most photogenic, configuration.)
So why was this amazing instrument shut down on January 11, 2010? Well, to make it better, of course! The VLA is being transformed into the EVLA, or the Expanded Very Large Array. It is being brought into the 21st century with a series of upgrades that will give it more than 10 times its current sensitivity and a host of new capabilities that have astronomers eager to explore the possibilities.
Some of these upgrades have been underway since 2001 and are already completed. Radio signals were brought from each antenna to a central location via a series of tubes (No, really. A series of tubes…) called waveguides. These hollow metal tubes allowed the radio light to be brought together and the signal digitized before coming to the central computer. The waveguides for the VLA have been replaced with fiber optics for the EVLA, which allows the data, now digitized at the antennas, to be brought to the center at a faster rate.
Each antenna got an upgrade as well, as one by one they were taken off to the antenna barn and refitted with all new feed horns and receivers. A feed horn is literally a metal horn that collects the radiation that has been reflected into it by the dish and sends it to be detected by the receiving system. The receivers detect the radiation and transmit it electronically to the next stages of the telescope system. In this way, it’s (very) roughly analogous to the CCD camera in an optical telescope, only it operates with just a single pixel. (That’s why systems of multiple antennas are really useful!) The new receivers have the ability to detect radiation at every frequency between 1 and 50 GHz (that’s 30 cm to 6 mm, for those of you who are spatially inclined.) The old system was only sensitive to certain small frequency windows within that range. With the EVLA, astronomers will be able to probe the universe more deeply at all of these frequencies, discovering new astrophysical phenomena along the way.
The final piece of the new EVLA infrastructure has been in development by the National Research Council in Canada and is now being hooked up to the array in New Mexico. This is the reason for the temporary closure. I’m talking about the WIDAR Correlator. A correlator is the specialized central computer for an interferometer. It brings all the signals from the individual antennas together so that astronomers can make an image or measure a spectrum. WIDAR stands for Wide-band Interferometric Digital ARchitecture. Let’s parse that. We know it’s a digital system, and that it is being used for interferometry. Wideband means that it can accommodate a wide range of frequencies at once. More frequencies… means more light… which means better sensitivity… which means dimmer objects can be observed! This is where much of the power of the new EVLA system will come from.
(For you radio astronomy nerds, we’re talking 8 GHz of simultaneous bandwidth, with is 80 times better than the best done by the original VLA, with 16,384 spectral channels, a far cry better than the current 16 channels. The maximum number of spectral channels is 4,194,304. I’ll repeat that… 4,194,304 spectral channels at it’s finest resolution… compared to the 512 channels for the VLA. That’s a frequency resolution, at it’s finest, of 0.12 Hz, more than 3000 times better than the current system. For those of you that could care less about the jargon, that’s ridiculously, stupid good.)
This fantastic new correlator will come back online, slowly at first, in March of this year. The EVLA will be up to it’s full functionality in 2012. Science will be done the whole way there, slowly, cautiously, shaking out all the bugs in the system as they go along. When it is finished it will be a versatile, powerful telescope, and much easier to use for the general astronomical community.
If you are ever in central New Mexico, I highly recommend a visit to the EVLA! Self-guided tours are available every day from 8:30 am until dusk… just be sure to head inside if you hear the lightning alarms… or see a rattlesnake. Special guided tours will be offered on April 3rd to correlate with one of the two times a year that the Trinity Site is open. Guided tours are also offered on some days during the summer by the lovely NRAO summer students. Check out the website www.vla.nrao.edu for details. If you can’t make it out there, be sure to check out some gorgeous images of and from the VLA at the NRAO’s image gallery images.nrao.edu. More information about the EVLA can be found at www.aoc.nrao.edu/evla. All of these links will be included in the show notes and at my website, noisyastronomer.com.
Thank you for listening! (And, uh, the VLA is not a, uh, an awful waste of space.)
I now leave you with Dorian Spencer and his song, “New Mexico.”
End of podcast:
365 Days of Astronomy
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