A Search for Monochromatic Light Toward the Galactic Centre

TL;DR

This study conducted an extensive optical survey of the Galactic Centre using a novel instrument to detect monochromatic laser signals, but found no evidence of extraterrestrial optical communication, adding to the SETI non-detection record.

Contribution

The paper introduces a new high-resolution, wide-field optical instrument capable of detecting monochromatic signals, and applies it to a large region of the Galactic Centre for SETI.

Findings

No monochromatic optical signals detected in 34800 exposures

Detected laser signals would be observable from 100 light years with 60 MW power

Results extend the non-detection record in optical SETI searches

Abstract

A region 140 square degrees toward the Galactic Centre was searched for monochromatic optical light, both pulses shorter than 1 sec and continuous emission. A novel instrument was constructed that acquires optical spectra of every point within 6 square degrees every second, able to distinguish lasers from astrophysical sources. The system consists of a modified Schmidt telescope, a wedge prism over the 0.28-meter aperture, and a fast CMOS camera with 9500 x 6300 pixels. During 2021, a total of 34800 exposures were obtained and analyzed for monochromatic sources, both sub-second pulses and continuous in time. No monochromatic light was found. A benchmark laser with a 10-meter aperture and located 100 light years away would be detected if it had a power more than ~60 megawatt during 1 sec, and from 1000 light years away, 6000 MW is required. This non-detection of optical lasers adds to previous optical SETI non-detections from more than 5000 nearby stars of all masses, from the Solar gravitational lens focal points of Alpha Centauri, and from all-sky searches for broadband optical pulses. These non-detections, along with those of broadband pulses, constitute a growing SETI desert in the optical domain.