SETI & Technosignatures

Constraints On Extragalactic Transmitters Via Breakthrough Listen

By Keith Cowing
Press Release
September 19, 2022
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Constraints On Extragalactic Transmitters Via Breakthrough Listen
A plot of the Transmission Rate against EIRPmin for a range of SETI studies. The gray line is defined by the two most constraining values – this work (the results for NGC 7714/NGC 7715, the 3C402 galaxy group, and the nearby AGN WISEA J080816.59+210857.0) and that of Wlodarczyk-Sroka et al. (2020) – these data extend the parameter space into a new region of smaller transmission rates and larger EIRPmin. If extraterrestrial transmitters follow a power-law distribution, the region below this line represents a “terra incognita” for SETI surveys. The error bars of this work (red symbols) are presented at the 2-sigma level for clarity.

The Breakthrough Listen Initiative has embarked on a comprehensive 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 NED were employed to make a rudimentary census of extragalactic objects that were serendipitously observed with the 100-m Greenbank telescope observing at 1.1-1.9 GHz. For 469 target fields (assuming a FWHM radial field-of-view of 4.2 arcminutes), NED identified a grand total of 143024 extragalactic objects, including various astrophysical exotica e.g. AGN of various types, 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, place stronger limits on the prevalence of extraterrestrial intelligence in the distant Universe than is often fully appreciated.

M.A. Garrett, A.P.V. Siemion

Comments: 9 Pages, 5 figures, accepted by MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA); Popular Physics (physics.pop-ph)
Cite as: arXiv:2209.08147 [astro-ph.HE] (or arXiv:2209.08147v1 [astro-ph.HE] for this version)
Submission history
From: Andrew Siemion
[v1] Fri, 16 Sep 2022 19:36:07 UTC (8,847 KB)

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