Breakthrough Listen found no artificial radio signals in 97 galaxies

Astronomers from the Breakthrough Listen Project surveyed trillions of stars in 97 galaxies and compiled the results of the largest survey of radio signals from extraterrestrial civilizations. All discovered events are related to man-made signals. This article was published in Astronomy Journal. Breakthrough Listen started in 2015. Search for techno-signatures of extraterrestrial civilizations across a wide range of wavelengths, from light to radio. Various telescopes around the world are participating in the observations. Observations include exoplanets, stars near the Sun, the Milky Way, and other galaxies.

A team of astronomers led by Carmen Choza of the University of California, Berkeley, is investigating new sources of extraterrestrial radio signals of an artificial nature as part of Breakthrough Listen, one of the largest surveys of the sky of any kind. The results of the survey were announced. The scientists searched for a narrowband drifting frequency signal (drift rate ±4 Hertz/second) with a minimum threshold of 33 for the signal-to-noise parameter.

Observations were carried out in 2019 and 2022 using the 100-meter Green Bank Radio Telescope in the frequency ranges 1.1-2.7 GHz and 4-11.2 GHz with high spectral and temporal resolution. The target sample consisted of the central regions of 97 galaxies of various types, including spiral galaxies, elliptical galaxies, irregular galaxies, and dwarf spheroidal galaxies. The distance to the galaxy varies between 60 kiloparsecs (dwarf galaxy Ursa Minor) and 29.2 megaparsecs (NGC 5813). A total of 1,519 signals were detected, but further investigation did not reveal a single case that was not related to various types of human RF interference.

This places a maximum limit of about 3 percent on the number of nearby galaxies that can have narrowband transmitters with detectable equivalent isotropic radiation power of about 1024 watts.