The impact of gravitational microlensing on searches for extraterrestrial intelligence at optical wavelengths

Abstract

The search for extraterrestrial intelligence (SETI) at optical wavelengths counts photons from target stars. The rationale is that the number of photons received from a solar-type star in a nanosecond is typically much less than unity and that an excess number of photons may be indicative of a laser pulse from a technological civilization. Extreme magnification gravitational microlensing is a possible contaminant to optical SETI programs as it would increase the photon rate and could masquerade as an optical pulse. We show that extreme magnification gravitational microlensing is unimportant, both because the required amplifications are difficult to obtain and because the time scales are too large. This conclusion holds both for the case of background stars in the field of view of the target star and from objects (such as planets) orbiting the target star.