SETI & Technosignatures

Upper Limits On Transmitter Rate Of Extragalactic Civilizations Placed By Breakthrough Listen Observations

By Keith Cowing
Status Report
April 10, 2023
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Upper Limits On Transmitter Rate Of Extragalactic Civilizations Placed By Breakthrough Listen Observations
Upper limits on the transmitter rates as a function of EIRPmin in this work and previous studies are presented. The dot-dash lines show our result for the case of GBT-L, using the statistical method described in Section 3.2.1. The results based on the crossmatching method are shown in arrows, with different colours corresponding to different surveys. Other markers in different colours represent the upper limits presented in previous studies (Gray & Mooley 2017; Enriquez et al. 2017; Price et al. 2020; Wlodarczyk-Sroka et al. 2020; Garrett & Siemion 2023). The grey dotted line connecting the previous most constraining values reported by Wlodarczyk-Sroka et al. (2020) and Garrett & Siemion (2023) was introduced as terra incognita (Garrett & Siemion 2023). The terra incognita indicates the line below which the parameter space needs to be explored at better sensitivity and a broader search area. — astro-ph.HE

The Search for Extra-Terrestrial Intelligence (SETI) has been conducted for over sixty years, yet no technosignatures have been identified. Previous studies have focused on stars in our galaxy, with few searches in the extragalactic Universe despite a larger volume being available.

Civilizations capable of harvesting energy from a star or a galaxy are classified as KII or KIII on the Kardashev scale, respectively. Technosignatures from such advanced civilizations would be extremely luminous and detectable by current radio telescopes, even from distant galaxies. To explore the frontier of extragalactic SETI, we investigate the likely prevalence of extragalactic civilizations possessing a radio transmitter, known as the transmitter rate, based on observational results from the Breakthrough Listen (BL) observations.

We calculated the transmitter rate by considering the background galaxies in the field of view of target stars in BL observations. We used a statistical method to derive the total mass of stars in those background galaxies from a galaxy stellar mass function.

Our statistical method suggests that less than one in hundreds of trillions of extragalactic civilizations within 969 Mpc possess a radio transmitter above 7.7×1026 W of power, assuming one civilization per one-solar-mass stellar system. Additionally, we cross-matched the BL survey fields with the WISE×SuperCOSMOS Photometric Redshift Catalogue and compared with the statistical method.

Our result sets the strictest limits to date on the transmitter rate at such high power levels, emphasizing the high efficiency of searching for radio transmitters in galaxies and the rarity of technologically advanced civilizations in our Universe.

Yuri Uno, Tetsuya Hashimoto, Tomotsugu Goto, Simon C.-C. Ho, Tzu-Yin Hsu, Ross Burns

Comments: 5 pages, 1 figure, accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2304.02756 [astro-ph.HE] (or arXiv:2304.02756v1 [astro-ph.HE] for this version)
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Submission history
From: Yuri Uno
[v1] Wed, 5 Apr 2023 21:39:43 UTC (307 KB)

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