Very Long Baseline Array (VLBA)

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Overview

The National Radio Astronomy Observatory

[Adapted from NRAO website materials]

Founded in 1956, the National Radio Astronomy Observatory (NRAO) is one of the world's premier research facilities for radio astronomy. NRAO operates powerful, advanced radio telescopes spanning the western hemisphere. Scientists from around the world use these instruments to probe fundamental questions in astronomy and physics. 

NRAO is a research facility of the U.S. National Science Foundation and acts as a national facility providing state-of-the-art radio telescopes and support instrumentation for use by the entire scientific community.   NRAO designs, builds, operates and maintains radio telescopes that are used to study virtually all types of astronomical objects known, from planets and comets in our own Solar System to quasars and galaxies billions of light years away.

NRAO has its headquarters in Charlottesville, VA, and operates major radio telescope facilities at Green Bank, WV; Socorro, NM; and Tucson, AZ. The NRAO is operated for the National Science Foundation by a consortium of universities known as Associated Universities, Inc., under a cooperative agreement. 

The Very Long Baseline Array (VLBA )

[Adapted from: Dave Finley essay on the NRAO - VLBA website]

The Very Long Baseline Array, one of the major instrument facilities managed by NRAO, is a series of ten radio antennas spread across the United States and its territories from St. Croix, the Virgin Islands, to Mauna Kea, Hawaii. The operations center for the array is located in Socorro, New Mexico. Astronomical data from the observations are recorded on digital tape at each antenna site. The tapes are then shipped to the Socorro Operations Center where they are correlated and the results sent to the investigators.

Each VLBA station consists of an 82-foot (25-meter) diameter dish antenna and an adjacent control building which houses the station computer, tape recorders and other equipment associated with collecting the radio signals gathered by the antenna. Each antenna weighs 240 tons and is nearly as tall as a ten-story building when pointed straight up. The ten radio antennae work together as the world's largest dedicated, full-time astronomical instrument. Construction began in February, 1986, and was completed in May, 1993. The first observation using all ten sites occurred May 29, 1993. Total construction cost was $85 million.

The Array Operations Center

From the Array Operations Center (AOC) in Socorro, New Mexico, the VLBA operators are able to remotely control and monitor the stations over the Internet. The operators can aim the antennas, select radio frequencies for observation, control the tape recorders and monitor the 'health' of the equipment at every site. A real-time display of the array's status is available for observers to monitor their observations.

The Correlator

Data recorded at each VLBA site is sent back to the AOC for processing at the correlator, a special-purpose high-performance computer that combines the data from each station to produce a single set of data from which high-resolution images can be made. The correlator performs the complex mathematical operations that actually allow the antennas of the VLBA, plus up to ten other radio telescopes around the world, to function as a single instrument. The correlator, designed and built by NRAO, is capable of performing 750 billion multiplications per second.

The Finished Product

The output from the correlator is provided to the astronomer(s) involved with the observation and further analysis and processing is performed on the data. This can occur at the AOC or at the observer's home university or institution. Depending on their scientific objectives, researchers can make images in a variety of forms, including both black-and-white and color formats.

Other NRAO Sites:

Major instruments at Green Bank include the largest fully steerable radio telescope in the world, named the Robert C. Byrd Green Bank Telescope (GBT).  A 140-foot equatorially mounted radio telescope on the site was decommissioned in 1999, and a host of smaller instruments.   The Very Large Array (VLA),  located on the Plains of San Agustin, 60 miles west of Socorro, New Mexico, was depicted in the movie Contact starring Jodie Foster.  The interferometric array consists of 27 antennas, each measuring 25 meters (81 feet) in diameter and weighing approximately 200 tons.  The newest telescope project of the National Radio Astronomy Observatory is the Atacama Large Millimeter Array (ALMA) Project. This endeavor includes the collaboration of observatories from around the world in the manufacturing of 64 12-meter antennas. The site is located at an elevation of 16,400 feet in Llano de Chajnantor, Chile.