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Tuesday
Jul242012

The Very Large Array: It is what it is

by Sarah Scoles

 

Or, at least, that's what the bottle opener at the gift shop says.

Last week, I spent some time at the newly re-christened Karl G. Jansky Very Large Array (hereafter, as the official memo said to do after the first reference to the new name, just the VLA) and at its associated operations center in Socorro, NM.

During this trip, Sue Ann Heatherly and I were leading a workshop for teachers interested in becoming part of the Pulsar Search Collaboratory, which, historically, has been an Eastern and Midwestern US program. Currently, more than 700 students and their associated 80 teachers have learned how to analyze survey data from the Green Bank Telescope to find new pulsars.

To date, they've found six never-before-seen pulsars. The latest discovery (not on the website) was discovered during the workshop held just two weeks ago in Green Bank. In an unanalyzed dataset on which students were practicing their scientific skills, three students found a pulsar that rotates six times every second. We had no idea it was in there--the 137 datasets we put up had approximately a 1% chance, given the number-of-pulsars-per-terabyte rate we've observed, of containing a pulsar.

Now, this program is expanding to the Southwest. So we spent the weekend talking about dispersion measure and phase and reduced chi-squared and histograms. And also eating green chiles and taking pictures like this:

and this

The VLA recently got not a face-lift, but, like, a brain-and-vein lift. It has a new correlator (WIDAR), a "computer" of sorts, but one that can do 10^16 operations per second to handle the 1.2 gigabit per second data rate. What that means is that the new VLA produces as much data in 100 seconds as the old VLA did during its whole 30-year life.

The VLA is an interferometer, meaning that it points a lot of antennae (like the one above) at the same object in space, and all of those telescopes act like one gigantic telescope--a telescope that is as big as the largest distance between the antennae (more about interferometers).

Powerline? Is that you?On the Plains of Saint Augustin, 7000 feet in elevation, the VLA's 27 antennae can be separated by a maximum distance of 22 miles, causing them to simulate a telescope 22 miles in diameter. This is a lot easier for structural engineers than building a 22-mile-diameter telescope, which would surely collapse and kill everyone.

The bigger a telescope, the better its resolution. With the VLA, astronomers can make maps of structures many, many, many light-years away.

Below, I'll highlight a few of the most recent papers published using data from the revamped, wave-of-the-future VLA. AKA, the WTF VLA (note: this is my personal name for it and does not reflect any official naming convention).

ResearchBlogging.org

Law, Casey J & Bower, Geoffrey C. (2012). ALL TRANSIENTS, ALL THE TIME: REAL-TIME RADIO TRANSIENT DETECTION WITH INTERFEROMETRIC CLOSURE QUANTITIES. ApJ, 615 (2) DOI: 10.1088/0004-637X/749/2/143


Two people at Berkeley found a new way to detect fast radio transients (astronomical radio sources that turn on and off or get bright and then go dim) in real-time. So if you looked at the sky and something was there and then it was not (and then it was there and then it was not, even if the on-off-bright-dim only differed by milliseconds), astronomers would be able to find out right away. With arrays like the VLA, the locations of these pulsing or pulsating objects can be pinned down exactly, because the telescope's resolution is so good. When you have not only time resolution, but also spatial resolution, you can determine more about what is pulsing. Exoplanets, active stars, pulsars, and objects outside our own galaxy have quickly varying radio emission. This new method will be used with VLA data to learn more about astronomical sources that change their minds every 10 milliseconds.

 


 

Strader, Jay; Chomiuk, Laura; Maccarone, Thomas; Miller-Jones, James; Seth, Anil; Heinke, Craig; Sivakoff, Gregory. (2012). NO EVIDENCE FOR INTERMEDIATE-MASS BLACK HOLES IN GLOBULAR CLUSTERS: STRONG CONSTRAINTS FROM THE JVLA. The Astrophysical Journal, 142 (2) DOI: 10.1088/2041-8205/750/2/L27

Globular Clusters: A great name for a new candy (Credit: Science Buddies)

These astronomers wanted to use the VLA to find intermediate-mass black holes (not tiny ones, not ones the mass of the sun, and not ones as big as at the center of the galaxy) in three globular clusters--the dense groupings of stars that orbit the Milky Way.

They did not see any evidence for IMBHs, which either means

  • Globular clusters don't usually have black holes at their centers.
  • Not much material falls onto IMBHs in globular clusters, so we cannot detect them even though they're there. More about how we "see" black holes.

 


Ragan, Sarah; Heitsch, Fabian; Bergin, Edwin; Wilner, David. (2012). Very Large Array Observations of Ammonia in Infrared-Dark Clouds II: Internal Kinematics. The Astrophysical Journa, 502 (2) DOI: 10.1088/0004-637X/746/2/174


Astronomers believe that IRDCs--infrared-dark clouds--are where high-mass star fetuses incubate. These cold clouds of gas, as their helpful name suggests, are dark in the infrared but can be detected with radio telescopes. The molecule ammonia, which emits radio waves, traces out areas these high-mass stars are being conceived (gross!) and can tell us about the way particles within the cloud are moving around. In this study, astronomers determined that the movement of ammonia in IRDCs shows evidence that the clouds are actively breaking apart and collapsing, which they must do in order to form stars.


Wright, Melvyn; Zhao, Jun-Hui; Sandell, Goran; Corder, Stuartt; Goss, W.M.; Zhu, Lei. (2012). Observations of a high-mass protostar in NGC 7538S. The Astrophysical Journal DOI: arXiv:1201.0944v1

Proto-star (Credit: Toddlers and Tiaras, duh).Protostars are, as their name suggests, the things that come before stars. In giant molecular clouds, the gravitational energy between particles is usually balanced out, so that the gas particles remain far enough apart that they don't get together and get all dense. However, disturbances in that equilibrium can lead parts of the cloud to become clumpy, gravitationally bind, and to accrete more mass (because they have more mass in a centralized location and thus have more gravitational effect on the surrounding material).

A recent VLA project looked at one of these pre-stars--NGC7538S, which is high-mass for one of these objects--and made an image. By comparing this image with images from infrared telescopes, astronomers can determine the size, spatially, of the dust cloud surrounding the protostar, as well as the mass of the material falling onto the protostar--which turns out to be about 60 times the mass of the sun.

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Reader Comments (1)

I love hearing the new research coming out of the VLA upgrade!

It's incredible that in 100 seconds you get the same amount of data from the last 30 years. Blows. My. Mind.

July 27, 2012 | Unregistered CommenterBrooke

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