For nearly a decade, the European Space Agency’s Gaia Observatory has been continuously operating at the Earth-Sun L2 Lagrange Point. Gaia’s goal as an astrometry mission is to collect information on the locations, proper motion, and velocity of stars, exoplanets, and objects in the Milky Way and tens of thousands of neighboring galaxies. Gaia will have viewed an estimated 1 billion celestial objects by the end of its primary mission (planned to end in 2025), resulting in the compilation of the most precise 3D space database yet created.
To present, the ESA has produced three data releases from the Gaia mission, the most recent (DR3) in June 2022. In addition to the advances enabled by these releases, scientists are discovering new applications for this astrometric data. A team of astronomers has proposed that the variable star catalog from Gaia Data Release 3 could be utilized to aid in the Search for Extraterrestrial Intelligence (SETI). Scientists could narrow the hunt for extraterrestrial broadcasts by coordinating the search with notable events (such as a supernova!).
Andy Nilipour, an undergraduate student at Yale University’s Department of Astronomy, led the research. He was joined by James R.A. Davenport, a Research Scientist at the University of Washington in Seattle; Adjunct Senior Astronomer Steve Croft from the Radio Astronomy Lab and the SETI Institute at UC Berkeley; and Andrew Siemion, the Bernard M. Oliver Chair for SETI Qualification at UC Berkeley, the University of Manchester’s Jodrell Bank Centre for Astrophysics (JBCA), and the University of Malta’s Institute of Space Sciences and Astronomy.
Nilipour’s first academic paper was published in The Astronomical Journal (“Signal Synchronization Strategies and Time Domain SETI with Gaia DR3”). “My two mentors, Steve Croft and James Davenport, chose this for me, the idea of developing a geometric technique for constraining [technosignature] searches,” he revealed in an interview with Yale News. Because there are so many possibilities for the location of a broadcast and the form of the signal, it’s perhaps the most difficult task in SETI right now.”
Simply put, technosignatures are signs of activity that unequivocally indicate the presence of a sophisticated technological society. To date, the vast majority of SETI investigations have searched for radio signals because the technology is known to be practical and radiowaves propagate well through space, with Breakthrough Listen being the most advanced and extensive. These tests also included listening to different stars for a specified amount of time in the hopes of detecting radio signals from circling planets. However, scientists have recently broadened the field of probable technosignatures and]considered other ways as well. Nilipour stated:
“There are numerous ideas regarding how technosignatures might appear. The most common form we seek for is narrowband radio emission, because this appears to be something that a technological civilisation should be producing based on our sample size of human technology. Other possibilities include laser emission, close collisions of stars at high speeds, and emission from a star that suddenly and significantly decreases.”
Nilipour and his colleagues hypothesized that an intelligent society would recognize how difficult it is to monitor all of the space surrounding their planet in every imaginable mode – radio, optical, infrared, ultraviolet, x-ray, gamma-ray, and so on. As a result, they may choose to time their greeting signals (fingers crossed!) with a prominent astronomical event that will catch the attention of observers, such as supernovae. Nilipour began working on this hypothesis as part of a summer undergraduate program sponsored by the National Science Foundation (NSF) and the Berkeley SETI Research Center’s Breakthrough Listen Initiative.
First, Nilipour and his colleagues looked at the time it took for light from four historical supernovae to reach Earth in the last 1,000 years. Nilipour elucidated:
The ellipsoid approach, which synchronizes signals to a prominent astronomical event, and the Seto method, which is based on geometric angles rather than distance, were combined and used to four events. We selected four supernovae that have been historically recorded in the years 1054, 1572, 1604, and 1987, respectively. In this situation, a supernova would function as a lighthouse, providing us, the signal’s receiver, with a common focal point.
They found that it took, respectively, 6,300, 8,970, 16,600, and 168,000 years for the light from these four events to arrive on Earth. They next contrasted these findings with light signals from more than 10 million stars in the DR3 catalog that had been detected by the Gaia observatory and recorded by it. This identified 403 stars whose light signals traveled to Earth from a favorable angle in regard to these supernovae and 465 stars whose light took the same amount of time to reach Earth. Despite the fact that none of the 868 systems produced any proof of technosignatures, their findings have supplied significant limitations for future searches.
As Nilipour pointed out, their approach can also be used to comb through other types of historical data to look for potential technosignatures:
“Finding a techno signature would have been amazing, but the actual purpose of this was to demonstrate a process that we can utilize going forward. As more data from TESS [the Transiting Exoplanet Survey Satellite] and other sources become available, what we’ve done here can be applied to those as well. The closest supernova in more than ten years, a new supernova in the galaxy M101, became visible in May of this year, and we are currently performing the same type of analysis utilizing it.
Searching for prospective technosignatures is a formidable endeavor given the number of stars in our galaxy alone, the amount of background noise, the time-sensitive nature of transmissions, and (as if that wasn’t enough) the possibility of receiving false positives. If every sector of the sky could be monitored forever and in numerous wavelengths at the same time, it would only be a matter of time before communications could be heard (if anyone out there was sending). Unfortunately, we do not have the time or resources to provide such comprehensive all-sky coverage.
This is where research like this comes in handy, since it efficiently narrows the search by investigating various sorts of technosignatures, frequency ranges, and places in the night sky. SETI researchers are gradually increasing the likelihood of an unambiguous detection that can be confirmed by follow-up studies. If there is a needle in the cosmic haystack, we will discover it sooner or later. Despite the constraints imposed by such a vast Universe and an infinite number of options, it is still only a matter of time.