A search for monochromatic light towards the Galactic Centre

Abstract

A region 140 square degrees towards the Galactic Centre was searched for monochromatic optical light, both pulses shorter than 1 s and continuous emission. A novel instrument was constructed that obtains optical spectra of every point within 6 square deg every second, able to distinguish lasers from astrophysical sources. The system consists of a modified Schmidt telescope, a wedge prism over the 0.28-m aperture, and a fast CMOS camera with 9500 × 6300 pixels. During 2021, a total of 34 800 exposures were obtained and analysed for monochromatic sources, both subsecond pulses and continuous in time. No monochromatic light was found. A benchmark laser with a 10-m aperture and located 100 light years (ly) away would be detected if it had a power more than ∼60 megawatt (MW) during 1 s, and from 1000 ly 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.