Unexplained starlight pulses found in optical SETI searches

Years spent searching more than 1300 sun-like stars for optical SETI signals have finally yielded unexpected results. A “signal” of two fast identical pulses, separated by 4.4s, was discovered in the light of HD89389. No single pulses, even remotely resembling these, have been found in these searches. Close examination of this signal reveals that several unique features of the first pulse are repeated almost exactly in the second. Comparison of this signal with those of airplanes, satellites, meteors, lightning, atmospheric scintillation and system noise, emphasizes their uniqueness. During the re-examination of historical data, another pair of similar pulses was found in an observation of HD217014 made four years earlier. Not fully explained at the time, this signal had been dismissed simply as “birds.” After all pulses were examined in detail, and shown that they could not have been made by birds, several theories are proposed that might explain their origin. A theory based on edge diffraction is discussed in some detail. If correct, this theory should enable future observations to measure the distance to the occulting object, and using arrays of telescopes, determine its size, shape and velocity. • Fast optical photometry of stars, 100 microsecond samples, reveals strange signals. • Unknown source modulates starlight brighter and fainter in fraction of a second. • Source of starlight modulation invisible in photographs. • Arrays of synchronized optical telescopes could to explain dual starlight pulses. • More fast optical searches needed of sun-like stars.