“Using the huge mirror area of the four VERITAS telescopes will allow us to search for extremely faint optical flashes in the night sky, which could correspond to signals from an extraterrestrial civilization," said Holder.

Over the next year, the Breakthrough Listen team will complete a survey of 1702 stars looking for evidence of signals from advanced civilizations using telescopes capable of receiving radio waves. 

Led by Holder at UD and Williams at UC Santa Cruz, the VERITAS team will survey a subset of these stars, about 120 in all, looking for optical beacons, or pulses of light, using the four 40-foot telescopes located at the Fred Lawrence Whipple Observatory in Arizona. (The nearest town, Amado, is about eight miles away, with Tucson about 42 miles to the north.) Earlier in 2019, Holder and other VERITAS researchers reported on new ways to measure distant stars. In 2018, they detected once-in-a-lifetime gamma rays.

"Breakthrough Listen is already the most powerful, comprehensive and intensive search yet undertaken for signs of intelligent life beyond Earth," said Andrew Siemion, director of the Berkeley SETI Research Center and leader of the Listen team. "Now, with the addition of VERITAS, we're sensitive to an important new class of signals: fast optical pulses. Optical communication has already been used by NASA to transmit high definition images to Earth from the Moon, so there's reason to believe that an advanced civilization might use a scaled-up version of this technology for interstellar communication."

UDaily caught up with Holder and UD doctoral student Gregory Foote, who also is involved in the work, to talk about their hopes for the project.

Q: What will you be looking for?

Holder: The VERITAS telescopes are big mirrors with very sensitive light detectors that will be looking for pulsed optical beacons with durations as short as a few billionths of a second. There are things going on in our atmosphere that produce flashes that last this long: the gamma rays that I study produce a blue flash of light when they come in contact with the Earth’s atmosphere.

With the Breakthrough Listen project, the signals or pulses of light that we are looking for would come from as far away as the stars — hundreds to thousands of light-years from Earth. We would expect a laser-like pulse to look like a small, focused point that lasts only a few billionths of a second. And their signatures would appear exactly the same in each image recorded by cameras on the four VERITAS telescopes. This is the real discriminating factor … that it appears on all four telescopes from exactly the same location in the sky.

Q: Would you define a light-year?

Holder: A light-year is simply the distance that light travels in one year. Put into context, light from the sun takes eight minutes to reach Earth, but to get to the stars we’re studying, it would take 1,000 years. If an advanced civilization from 1,000 light-years away sent us a pulse, it would take the signal 1,000 years to reach Earth. 

Q: What do you think you will find?

Holder: People have been looking for a while and they haven’t seen anything, but the universe is big and we’ve only explored a tiny fraction of it. Lasers have already been used by NASA to transmit signals within our solar system, so it stands to reason that in space someone may be able to send a signal powerful enough for us to spot. And artificial beacons would easily outshine any stars that lie in the same direction on the sky at these timescales, so it makes sense to look.

Q: How did you choose which stars to point the VERITAS telescopes at?

Foote: Jamie and I devised a scoring algorithm to select the stars we planned to target from Breakthrough Listen’s list of candidates. We whittled the list to around 500, throwing out stars that were invisible to our telescopes, located below the horizon or too far away. We refined the list based on star brightness, whether it had exoplanets or whether it was close to another candidate so that we could “double up” on observations. Ultimately, we settled on 120 targets to observe.

Q: What if you see something?

Holder: We are looking at each target star for approximately 15 minutes. If we saw a signal during that 15-minute period, the first thing we would do is go back and have the telescopes stare at that star for another 20 to 30 hours to see if the pulse repeats itself. There are other telescopes around the world, too, that we could ask to look for a signal coming from the exact same position in the sky. 

Q: How would you confirm that a pulse signal is a sign of communication?

Holder: We would first do everything possible to explain any pulse signal in natural terms. When pulsars were discovered in the 1960s, one of the first possibilities considered was that they were signals produced by an advanced civilization. Scientists determined, however, that pulsars were actually the spinning heart of a dead star. Every time the star spun around, a radio beam would flash by, similar to the rotating beacon from a lighthouse flashing at night, and produce a pulsed emission that sounded like the tick-tick-tick of a clock.

In our case, the clearest indication for a signal not being natural would be if there was some sort of intelligence coded in the pulse of light. Say you see more than one pulse, and that pulse counts — first one pulse, then two pulses, then three pulses — this is someone trying to send you information. Obviously, if we saw something like this we’d get interested.

Q: How did the idea for this project come about?

Holder: I was trying to look up how to build a particular circuit for my gamma ray research. I Googled Paul Horowitz, a Harvard physicist who wrote a famous electronics book, and saw something about him searching for optical pulses using a small telescope. I thought, “we can do this for free with VERITAS, we’ve already built these telescopes.” Then I read about Boyajian’s Star. For some reason the light coming from this otherwise normal star dips from time to time, sometimes as much as 20%. People questioned whether there could be massive advanced civilization structures around the star that were obstructing our view, causing the stars’ brightness to dim. It turned out we had about 10 hours of observations on this exact star in the VERITAS data archive because it landed near a gamma ray target we were studying. I analyzed the data while on sabbatical in 2015-16 and wrote up a paper that described the technique that led to the funding for this current study.

Q: What about this project is most exciting to you?

Holder: The universe has existed for billions of years, but at the moment there is no evidence of life anywhere except on planet Earth — not even bacteria or microbes. Finding evidence for intelligent life outside of Earth would be revolutionary.

Foote: I spent two weeks working at VERITAS last winter to become familiar with the telescope’s hardware and software. Sitting in the control room and moving these fantastic telescopes to a specific part of the sky was a surreal and exciting experience. Now I get to spend time trawling through data and designing ways to analyze it ... and I get to include it as part of my doctoral thesis.

This project is supported by a grant from the Breakthrough Initiatives. VERITAS is supported by the National Science Foundation, the Smithsonian Institution, the U.S. Department of Energy and the Natural Sciences and Engineering Research Council of Canada.

About the Breakthrough Initiatives

The Breakthrough Initiatives are a suite of scientific and technological programs, founded by Yuri Milner, investigating life in the universe. Breakthrough Listen is a scientific program in search for evidence of technological life in the universe. It aims to survey one million nearby stars, the entire galactic plane and 100 nearby galaxies at a wide range of radio and optical bands. Along with Breakthrough Listen, the Breakthrough Initiatives include Breakthrough Watch, an optical search for Earth-like planets in the habitable zones of nearby stars; and Breakthrough Starshot, the first significant attempt to design and develop a space probe capable of reaching another star.