Caltech's high-desert array monitors the entire northern sky continuously, catching radio flares from black holes and the explosive deaths of stars in real time.
PopePompus, CC BY-SA 4.0
A valley of cosmic ears
East of the Sierra Nevada, in a high-desert basin shielded from urban radio noise, the Owens Valley Radio Observatory (OVRO) has been mapping the cosmos since 1958. Operated by the California Institute of Technology (Caltech), the observatory began with a modest 32-foot (9.8-meter) antenna moved from Palomar Mountain. This was quickly followed by its first interferometer: a pair of 90-foot (27.4-meter) dishes on railroad tracks that could be repositioned to sharpen their view of the sky. This setup made some of the first detailed radio images of distant galaxies and determined that many consist of two distinct lobes of radio emission.
By 1968, a larger 130-foot (40-meter) telescope joined the facility. This instrument is a central part of the observatory's work. Since 2008, the 40-meter telescope has been dedicated to a program monitoring the radio emissions of over 1,800 blazars—galaxies with active supermassive black holes at their cores—in support of NASA's Fermi Gamma-ray Space Telescope. This long-term monitoring has showed how jets of particles are launched from black holes and helped observe a star being torn apart by a black hole for the first time at radio wavelengths.
Over the decades, OVRO hosted several pioneering instruments. From 1985 until 2005, it housed the Caltech Millimeter Array, a set of six 10.4-meter dishes that discovered new details about star-forming regions and protoplanetary disks. These dishes were later moved to a higher site to become part of the Combined Array for Research in Millimeter-wave Astronomy (CARMA), which operated until 2015.
The modern radio sky in real time
Today, OVRO is now focusing on large arrays of smaller, faster antennas designed for wide-sky surveys and transient detection. The Owens Valley Long Wavelength Array (OVRO-LWA) consists of 352 pyramid-shaped dipole antennas spread across the desert floor. Operating at low frequencies between 13 and 88 megahertz, it images the entire visible sky to hunt for faint signals, including radio bursts from exoplanet magnetospheres and the prompt radio counterparts to gravitational wave events.
Another major project is the Deep Synoptic Array (DSA). The current 110-dish version, DSA-110, is used for detecting and precisely locating Fast Radio Bursts (FRBs). These are millisecond-long, intensely powerful pulses of radio waves from deep space. By pinpointing their host galaxies, the DSA-110 helps astronomers understand the origins of these bursts. Plans are underway for a vastly more ambitious successor, the DSA-2000, which will consist of 1,650 dishes in Nevada. This future array will function as a "radio camera," producing images in real time and surveying the entire sky to detect over a billion radio sources.
The observatory also hosts the Expanded Owens Valley Solar Array (EOVSA), which uses a combination of new and refurbished antennas to study solar flares. It can capture the radio spectrum of a flare at over 400 frequencies every second, providing data on the largest explosions in our solar system.
💡Fun Facts
The first interferometer at OVRO, which became operational on Christmas Day 1959, was used to determine the offset between Jupiter's magnetic axis and its rotational axis.
The 40-meter telescope helped identify a supermassive black hole binary system, PKS 2131-021, by observing its remarkably regular, sinusoidal variations in radio brightness over 45 years.
The site is also a station for the Very Long Baseline Array (VLBA), a continent-spanning system of ten radio telescopes that work together as a single instrument.
The observatory's location between the Sierra Nevada and the White Mountains provides essential shielding from radio-frequency interference, creating a quiet environment for the sensitive telescopes.
The observatory is an active research facility with restricted access. It occasionally hosts public open house events; check the official website for announcements. Self-guided tours of the grounds may be possible but require checking in.
Admission
Free during public events.
Accessibility
The terrain around the observatory is flat, high-desert. Paths in designated visitor areas are generally accessible, but much of the site is natural, uneven ground.
