If intelligent extraterrestrials exist around the so-called ‘alien megastructure’ star, they haven’t been shooting lasers at Earth over the last half-decade. Researchers combed through six years of archived data reported no brief optical flashes from the tantalizing star. Still, their search revealed that existing telescopes could help in the Search for Extraterrestrial Intelligence (SETI) without interrupting existing science.
“The detection of nanosecond optical pulses from the night sky requires large-aperture mirrors instrumented with fast photon detectors,” the international group of researchers declare in their paper, which appeared the in the Astrophysical Journal Letters.
“Ground-based gamma-ray telescopes have identical requirements and can be used to search for SETI-like signals.”
First detected by NASA’s Kepler spacecraft, KIC 8462852 vaulted into the public eye last fall when a scientist suggested one potential cause for its unusual signals could be alien megastructures. The famous star quickly became a SETI object of interest, targeted by new observations with radio telescopes. Last winter, a team of astronomers turned the Boquete Optical SETI Observatory in Panama toward the star in search of any laser signals at the time, with no success.
But one team of scientists took a different approach. Instead of taking a new look at the star, they instead combed through six years of archived observations made by VERITAS, an array of four telescopes set up at the Fred Lawrence Whipple Observatory in southern Arizona. VERITAS was built to search for the interaction of high-energy gamma ray signals with Earth’s atmosphere, rather than alien laser signals, but its ability to detect short optical bursts makes it ideal. Though radio signals have dominated in SETI searches, scientists have also considered optical observations to be a promising method of communication between stars.
Like other gamma-ray telescopes, VERITAS searches for the high-powered signals indirectly, by registering images of cascades of particles moving through Earth’s atmosphere at near-light speeds. When a promising signal is captured by at least two of the four VERITAS telescopes, observations are recorded every two nanoseconds.
Since 2007, VERITAS registered approximately nine hours of observations with the intriguing star in the background. To weed out potential laser bursts from cosmic rays and other background events, the astronomers determined that they were looking for a point-like signal that appeared in the same place with the same intensity in all four telescope cameras.
“The most convincing signal would be given by multiple occurrences of such images at different times, each matching the star’s position,” they said.
With these criteria, the number of potential signals dropped from over 7 million to only 28. None appeared to originate from the star.
But the scientists don’t seem dismayed. Instead, they point to detections that they characterized as falling meteors and reflections off satellites as providing strong evidence that gamma-ray telescopes are capable of capturing point-like images at large distances. Between VERITAS and two other existing telescopes, they calculated that there are approximately 30,000 hours of archived observations covering a substantial fraction of the sky. These instruments, known as imaging atmospheric Cherenkov telescopes (IACTs) are making ongoing observations, and other similar instruments will soon be online. All of them should be capable of registering brief laser flashes that could be signals from another world while searching for gamma-ray bursts.
“Perhaps the most important conclusion of this work is that modern IACT arrays are effective tools to search for faint optical transients, with durations as brief as a few nanoseconds,” the researchers said.
“The observations are complementary to, and have no impact on, the scientific program in the gamma-ray domain.”