A Search for Laser Emission with Megawatt Thresholds from 5600 FGKM Stars

TL;DR

This study conducted a high-resolution spectroscopic search for extraterrestrial laser emissions from 5600 nearby stars, setting detection thresholds and finding no evidence of such lasers, thus constraining the prevalence of advanced civilizations.

Contribution

First large-scale spectroscopic survey targeting laser emissions from a diverse set of 5600 stars, establishing detection thresholds and ruling out certain models of extraterrestrial civilizations.

Findings

No laser emissions detected from any of the 5600 stars.

Detection thresholds ranged from 3 kW to 13 MW depending on wavelength and star.

Constraints placed on the fraction of Earth-like planets with civilizations beaming lasers.

Abstract

We searched high resolution spectra of 5600 nearby stars for emission lines that are both inconsistent with a natural origin and unresolved spatially, as would be expected from extraterrestrial optical lasers. The spectra were obtained with the Keck 10-meter telescope, including light coming from within 0.5 arcsec of the star, corresponding typically to within a few to tens of au of the star, and covering nearly the entire visible wavelength range from 3640 to 7890 angstroms. We establish detection thresholds by injecting synthetic laser emission lines into our spectra and blindly analyzing them for detections. We compute flux density detection thresholds for all wavelengths and spectral types sampled. Our detection thresholds for the power of the lasers themselves range from 3 kW to 13 MW, independent of distance to the star but dependent on the competing "glare" of the spectral energy distribution of the star and on the wavelength of the laser light, launched from a benchmark, diffraction-limited 10-meter class telescope. We found no such laser emission coming from the planetary region around any of the 5600 stars. As they contain roughly 2000 lukewarm, Earth-size planets, we rule out models of the Milky Way in which over 0.1 percent of warm, Earth-size planets harbor technological civilizations that, intentionally or not, are beaming optical lasers toward us. A next generation spectroscopic laser search will be done by the Breakthrough Listen initiative, targeting more stars, especially stellar types overlooked here including spectral types O, B, A, early F, late M, and brown dwarfs, and astrophysical exotica.