Very Large Array: 45 Years of Discovery

The Plains of San Agustin are a desert in the middle of southwestern New Mexico, a prehistoric ocean bed now surrounded by a ring of mountains. Isolated, yet 50 minutes to Socorro, home of New Mexico Tech, the state's premier STEM University. 

The environment: dry skies, stable weather, and low latitude. Conditions that make it a perfect site for one of the most used and versatile radio telescopes in the world. The Very Large Array, or VLA for short.

It all began 45 years ago, when astronomers found the site.

A radio telescope collects information about objects in space by receiving radio signals via an antenna. The dish of the telescope, or the surface the radio waves land on, is made very large to cover and get high quality images of large portions of the sky. This resulted in telescopes such as the one in Green Bank, West Virginia. With a dish 300 feet across, the telescope was able to listen to skies better than any before it. Its current iteration weighs more than 16 billion pounds and is 60 percent higher than the Statue of Liberty.

But these large telescopes presented an even bigger challenge - building a structure strong enough to support the weight of the dish. Thus came the idea of “radio interferometry”. 

Multiple radio telescopes could be connected via cable to create a large radio telescope (a process known as interferometry). The information of the telescopes could be combined together, like pieces of a puzzle. The disk would, in effect, be as large as the distance between the two furthest telescopes. The larger disk would then result in a better quality picture, like sharpening a blurry image or putting on glasses. This would make it steerable, easier to maintain, and most importantly, allow for visibility of the sky that wasn’t yet thought possible. 

To prove that the idea of multiple telescopes working together was even feasible, a team at Green Bank created the first radio interferometer on-site in 1959. The idea was that multiple radio telescopes, some distance away, would point at the same source. The signal arrives at slightly different times, giving a different interference pattern. The patterns of these telescopes are then combined together, and through the time delay scientists can learn positional information about the object. 

The first array consisted of only two radio telescopes, and at the time - it was completely theoretical. One such person who worked on the project, Campbell Wade, stated that “something that hasn’t got written down is that we hadn’t believed we could do it. It was all very mysterious”.

Two 85 foot telescopes had already been built. All that was left was to connect them, calibrate the data, and observe. And after months of trial and error, on June 1st in 1964, they finally did. 

With the concept proven, the newly formed National Radio Astronomical Observatory (NRAO) could move on to proposing its main project - the Very Large Array – a collection of 27 antennas. Working together, they could capture 80 percent of the sky. Other projects proposed at the time, such as the Owens Valley Array, were smaller and only to be used by a group of universities, but the Very Large Array could be used by observers all over the world. It was groundbreaking, ambitious, and very expensive.

It would take until 1972 for them to approve the project. But as the NRAO committee finally saw more than a decade of work realized, they couldn’t help but wonder how to decide its location. Campbell, however, was perfect for the job. The list of sites he was given varied from unusual to outright nonsensical. Several cities, like London and Houston, were provided for political gain, ignoring the quiet and dry conditions required for the telescope to work.

For Campbell's part, he personally visited many of the sites, testing the geographic map with an altimeter he had purchased from a decommissioned plane (and temporarily landing a flight early due to security). But when he arrived in the desert near Datil, New Mexico, the very first site, he immediately knew it was the perfect place. It was protected by mountains, in a bowl shape that could block unwanted radio signals. It was high in altitude and dry, making the signals from the sky clear. And, it was next to a technical university: New Mexico Tech. 

After going through the list, Campbell landed on Socorro, describing it as the standard to which he held all other sites. He would later have the opportunity to move to Socorro while managing the construction of the VLA and live in New Mexico for the rest of his career. 

While reflecting on the project he stated in 2003, "looking back on it… our youth, combined with the total dedication we all had to what we were doing, led to a superior result and it’s sitting right out there at the Plains of San Agustin right now”.

The VLA would go on to be important in many aspects of astronomical research, including finding ice on Mercury, investigating supermassive black holes, and discovering more about the center of the Milky Way Galaxy. It also has become an iconic part of popular culture, with sci-fi media such as the movie Contact and the recently released TV show Pluribus being filmed on site at the telescope. 

As the VLA celebrates its 45th anniversary uncovering the mysteries of the Universe, plans are underway to replace the current dishes with 160 new ones. The “next generation” VLA will continue to make Socorro, New Mexico a hub of scientific discovery.