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Galactic traversability: a new concept for extragalactic SETI

Published online by Cambridge University Press:  04 October 2021

Brian C. Lacki Open the ORCID record for Brian C. Lacki [Opens in a new window]
Brian C. Lacki*
Affiliation:
Breakthrough Listen, Astronomy Department, University of California, Berkeley, CA, USA
*
Author for correspondence: Brian C. Lacki, E-mail: astrobrianlacki@gmail.com
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Abstract

Interstellar travel in the Milky Way is commonly thought to be a long and dangerous enterprise, but are all galaxies so hazardous? I introduce the concept of galactic traversability to address this question. Stellar populations are one factor in traversability, with higher stellar densities and velocity dispersions aiding rapid spread across a galaxy. The interstellar medium (ISM) is another factor, as gas, dust grains and cosmic rays all pose hazards to starfarers. I review the current understanding of these components in different types of galaxies, and conclude that red quiescent galaxies without star formation have favourable traversability. Compact elliptical galaxies and globular clusters could be ‘super-traversable’, because stars are packed tightly together and there are minimal ISM hazards. Overall, if the ISM is the major hindrance to interstellar travel, galactic traversability increases with cosmic time as gas fractions and star formation decline. Traversability is a consideration in extragalactic surveys for the Search for Extraterrestrial Intelligence (SETI).

Keywords

Search for extraterrestrial intelligenceinterstellar travelgalaxiesinterstellar medium
Type
Research Article
Information
International Journal of Astrobiology , Volume 20 , Issue 5 , October 2021 , pp. 359 - 376
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Copyright
Copyright © The Author(s), 2021. Published by Cambridge University Press

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