Karl G. Jansky Very Large Array

A telescope made of telescopes

The Very Large Array was designed to give radio astronomers images as sharp as optical ones, by combining many dishes through aperture synthesis, the technique developed by Martin Ryle and others in the 1950s and 1960s. Construction began in 1973 on the Plains of San Agustin in New Mexico, at an altitude of 2,100 metres, and the first antenna was installed in 1975; the array was formally inaugurated in 1980.

The array has 27 antennas in a Y shape, on rails that allow them to be moved between four configurations, from 1 to 36 kilometres across; each configuration gives a different balance between resolution and sensitivity.

Karl Jansky and the new array

The array was renamed the Karl G. Jansky Very Large Array in 2012, after an upgrade that replaced the electronics, receivers and correlator and increased sensitivity by factors of up to ten. Karl Jansky, an engineer at Bell Telephone Laboratories, had discovered radio emission from the Milky Way in 1932.

The array has imaged the radio jets of galaxies, the radio afterglows of gamma-ray bursts, the disks around young stars and the flares of the black hole in our own galaxy. It was the setting of a film and a symbol for the public of radio astronomy.

Running a distributed instrument

The National Radio Astronomy Observatory operates the array from a control building at the site and an operations centre in Socorro. The same observatory operates the Very Long Baseline Array and, with international partners, plans the next-generation VLA, a much larger array. Data from the VLA are archived and openly available after a proprietary period.

An array that keeps being rebuilt

The VLA of today shares little electronics with the VLA of 1980. Its original dishes and track remain, but the receivers, the correlator and the data system have been replaced, and the upgrade completed in 2012 improved the continuum sensitivity by a factor of about five and the spectral capability by a factor of thousands. A well-designed structure can host several generations of instrumentation. The next-generation VLA, if built, will extend that idea by adding many more dishes. The observatory's history shows that long-lived facilities are renewed in layers, with the slowest-changing parts built to last.

Instruments and technologies

• 25 m antennas Twenty-seven dishes with a Cassegrain system, each 230 tonnes, moved along rails by a transporter.
• WIDAR correlator A digital processor that combines the signals from every pair of antennas, forming 351 baselines, to produce an image.
• Receiver bands Eight receiver bands from 1 to 50 GHz covering the main radio windows.

The people

• Karl G. Jansky Bell Labs engineer who discovered cosmic radio emission in 1932.

Timeline

• 1973 Construction begins.
• 1975 First antenna installed.
• 1980 Array formally inaugurated.
• 2012 Upgrade completed and array renamed for Karl G. Jansky.

Key lessons for observation today

• Many small instruments, one image A correlator combines the dishes into a telescope of the whole array's width. Combining independent sensors by coherent processing is the model for distributed observation.
• Reconfigure to the question Moving the antennas changes the resolution. Flexible networks can be re-arranged for the question being asked.
• Upgrade the electronics, keep the metal The 2012 upgrade renewed the receivers and correlator while keeping the dishes. Modular upgrade paths extend the life of infrastructure.

Sources

• Wikipedia, Very Large Array
• NRAO, Radio Sky: Forty Years of the Very Large Array
• Wikipedia, Karl Guthe Jansky