Argus Panoptes, the all-seeing, manyeyed giant of Greek mythology, is about to take physical form in the mountains of North Carolina. In October, an array of 38 small telescopes will begin monitoring a slice of visible sky 1700 times the size of the full Moon. Known as the Argus Array Pathfinder, it will register changes in the stars second by second, essentially making a nightlong celestial movie. Its developers hope it will pave the way for a much larger Argus Array with 900 telescopes that by 2025 could watch the entire visible night sky.
The Argus telescopes join others aiming to capture short-lived or rapidly changing astrophysical events, known as transients, including exploding stars, ravenous black holes, neutron star mergers, and maybe even stars briefly eclipsed by the long-postulated hidden planet in our Solar System. The full Argus Array would watch the sky with more mirror area than all other transient telescopes put together, says team leader Nicholas Law of the University of North Carolina, Chapel Hill.
“The potential is enormous,” says Igor Andreoni of the University of Maryland, College Park, who is not involved in the project. As well as catching real-time events, Argus will build an archive of images showing objects before they explode or change. “We’ll know the history of anything that happens in the sky above a certain brightness,” Andreoni says. “We’re entering a new era of time-domain astronomy with an explosion of different sorts of telescope design,” adds Carole Mundell of the University of Bath.
Argus aims to achieve its unique vision with hundreds of off-the-shelf telescopes, each just 20 centimeters across and watching a different patch of sky. The final array will match the light-gathering power of a telescope with a single 5-meter mirror, which typically costs hundreds of millions of dollars, but cheap components should keep Argus’s cost below $20 million, Law says. The challenge will come in stitching together the array’s 900 images into a single, seamless movie of the night sky. “We’ve spent an awful lot of time on the data pipeline,” Law says.
In 2015, his team built a smaller instrument called Evryscope. That had 27 telescopes, each 7 centimeters across, looking outward from the surface of a hemispherical dome. Its successes included spotting a stellar flare—larger than any seen before—from our nearest neighbor star Proxima Centauri, but the team wanted to scale up to see objects outside our Galaxy.
Instead of looking out from a dome’s surface, the Argus telescopes will sit in a 10-meter-wide bowl, all aiming out a single skylightlike window in a dome. Over the course of the night, the bowl and telescopes will pivot slowly to follow the stars as Earth rotates. To capture quick-fire images, designers plan to replace the charge-coupled device (CCD) light sensors used in most telescopes with complementary metal-oxide-semiconductor detectors, which can read out data in less than a second compared with many seconds for CCDs.
Grants totaling $1.3 million from the National Science Foundation (NSF) and Schmidt Futures, a philanthropic initiative, funded the 38-scope prototype. Law and colleagues expect to test it in the coming weeks before transferring it first to a site in the Appalachian Mountains near Chapel Hill for debugging and later to Mount Laguna Observatory in California. The team hopes to show off its capabilities before seeking NSF funding for the full Argus Array after the turn of the year.
Data from Argus Pathfinder and its successor will be freely available in real time, and the software will issue automatic alerts when it detects an event. That will allow other, larger telescopes to quickly swivel to the same spot in the sky and collect more detailed data, a boon for astronomers probing stellar outbursts such as flares, supernovae, and gamma ray bursts.
Observers normally don’t spot supernovae, for example, until hours after the event. “Getting closer in time means you get closer to the source” of the explosion, says Shrinivas Kulkarni of the California Institute of Technology, a pioneer in efforts to capture transients. If the progenitor star is bright enough, Argus might also record any sudden brightening or belches of gas before its death—possible precursors of the blast. “It makes history available in a very comprehensive way,” Kulkarni says.
If Argus had been up and running in 2017, it might have given an early glimpse of the light flash from the first ever recorded kilonova—a merger of two neutron stars—and enabled other telescopes to home in on it quickly. As it happened, gravitational wave detectors were the first to sense the merger, but they can’t pinpoint locations accurately and guide other telescopes. “We need simultaneous observations,” Mundell says.
Argus might even spot the elusive Planet 9, hypothesized to lurk in the outer Solar System. It may be too cold and faint to be seen directly. But as it moves across the sky it should make background stars briefly blink out. “Occultations are certainly a promising avenue when it comes to Planet 9,” says Konstantin Batygin of Caltech, who with colleague Mike Brown proposed its existence in 2016 from gravitational influences on other distant bodies. If Argus pulls off that discovery, it will certainly have lived up to its formidable namesake.
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