Minimal conditions for survival of technological civilizations in the face of stellar evolution

TL;DR

This paper explores how patience and stellar encounters can significantly reduce interstellar travel times, impacting the survival strategies of civilizations facing stellar evolution, and suggests many civilizations may exist as dispersed populations rather than around original stars.

Contribution

It demonstrates that waiting for close stellar passages greatly reduces interstellar travel times, influencing the potential longevity and dispersal of technological civilizations.

Findings

Interstellar travel time can be reduced by two orders of magnitude by waiting for close star passages.

Civilizations may survive stellar evolution by migrating to lower-mass stars or becoming dispersed.

The fraction of civilizations as diaspora can be comparable to those remaining around original stars.

Abstract

The ease of interstellar rocket travel is an issue with implications for the long term fate of our own and other civilizations and for the much-debated number of technological civilizations in the Galaxy. We show that the physical barrier to interstellar travel can be greatly reduced if voyagers are patient, and wait for the close passage of another star. For a representative time of $\sim$1 Gyr, characteristic of the remaining time that Earth will remain habitable, one anticipates a passage of another star within $\sim 1500$~AU. This lowers the travel time for interstellar migration by $\sim$ two orders of magnitude compared with calculated travel times based on distances comparable to average interstellar separations (i.e., $\sim$1 pc) in the solar vicinity. We consider the implications for how long-lived civilizations may respond to stellar evolution, including the case of stars in wide binaries, and the difficulties of identifying systems currently undergoing a relevant close encounter. Assuming that life originates only around G-type stars, but migrates primarily to lower mass hosts when the original system becomes uninhabitable, the fraction of extant technological civilizations that exist as diaspora can be comparable to the fraction that still orbit their original host stars.