Constraints on extragalactic transmitters via Breakthrough Listen observations of background sources

Monthly Notices of the Royal Astronomical Society, vol. 519, pp. 4581–4588

Abstract

ABSTRACT The Breakthrough Listen Initiative has embarked on a comprehensive Search for Extraterrestrial Intelligence (SETI) survey of nearby stars in the Milky Way that is vastly superior to previous efforts as measured by a wide range of different metrics. SETI surveys traditionally ignore the fact that they are sensitive to many background objects, in addition to the foreground target star. In order to better appreciate and exploit the presence of extragalactic objects in the field of view, the aladin sky atlas and NASA/IPAC Extragalactic Database (NED) were employed to make a rudimentary census of extragalactic objects that were serendipitously observed with the 100-m Green Bank Telescope observing at 1.1–1.9 GHz. For 469 target fields [assuming a full width at half-maximum (FWHM) radial field of view of 4.2 arcmin], NED identified a grand total of 143 024 extragalactic objects, including various astrophysical exotica e.g. active galactic nuclei (AGN) of various type, radio galaxies, interacting galaxies, and one confirmed gravitational lens system. Several nearby galaxies, galaxy groups, and galaxy clusters are identified, permitting the parameter space probed by SETI surveys to be significantly extended. Constraints are placed on the luminosity function of potential extraterrestrial transmitters assuming it follows a simple power law and limits on the prevalence of very powerful extraterrestrial transmitters associated with these vast stellar systems are also determined. It is demonstrated that the recent Breakthrough Listen Initiative, and indeed many previous SETI radio surveys, places stronger limits on the prevalence of extraterrestrial intelligence in the distant Universe than is often fully appreciated.

Authors 2

1. M. A. Garrett corresponding Aachen Leiden Observatory

   Leiden University · University of Manchester · Leiden Observatory

   Affiliation as printed

   Jodrell Bank Centre for Astrophysics (JBCA), Department of Physics and Astronomy, The University of Manchester , Alan Turing Building, Manchester M13 9PL, UK

   Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden, the Netherlands

2. Andrew P. V. Siemion

   University of Manchester · University of California, Berkeley · Search for Extraterrestrial Intelligence

   Affiliation as printed

   Berkeley SETI Research Center, University of California Berkeley , Berkeley, CA 94720, USA

   Jodrell Bank Centre for Astrophysics (JBCA), Department of Physics and Astronomy, The University of Manchester , Alan Turing Building, Manchester M13 9PL, UK

   SETI Institute , Mountain View, CA 94043, USA