Globular Clusters as Cradles of Life and Advanced Civilizations

TL;DR

Globular clusters, being ancient and densely packed stellar systems, may serve as promising sites for life and advanced civilizations due to their stable habitable zones, proximity, and potential for interstellar communication, despite some risks.

Contribution

This paper models globular clusters to identify stable habitable zones and evaluates their potential for hosting advanced civilizations, highlighting their suitability for SETI efforts.

Findings

Large regions in globular clusters can support long-term habitable planetary orbits.

Globular clusters may host more advanced civilizations than the Galactic disk.

Wide-orbit and free-floating planets increase habitable opportunities in clusters.

Abstract

Globular clusters are ancient stellar populations with no star formation or core-collapse supernovae. Several lines of evidence suggest that globular clusters are rich in planets. If so, and if advanced civilizations can develop there, then the distances between these civilizations and other stars would be far smaller than typical distances between stars in the Galactic disk. The relative proximity would facilitate interstellar communication and travel. However, the very proximity that promotes interstellar travel also brings danger, since stellar interactions can destroy planetary systems. However, by modeling globular clusters and their stellar populations, we find that large regions of many globular clusters can be thought of as "sweet spots" where habitable-zone planetary orbits can be stable for long times. We also compute the ambient densities and fluxes in the regions within which habitable-zone planets can survive. Globular clusters are among the best targets for searches for extraterrestrial intelligence (SETI). We use the Drake equation to compare globular clusters to the Galactic disk, in terms of the likelihood of housing advanced communicating civilizations. We also consider free-floating planets, since wide-orbit planets can be ejected and travel freely through the cluster. A civilization spawned in a globular cluster may have opportunities to establish self-sustaining outposts, thereby reducing the probability that a single catastrophic event will destroy the civilization or its descendants. Although individual civilizations within a cluster may follow different evolutionary paths, or even be destroyed, the cluster may always host some advanced civilization, once a small number of them have managed to jump across interstellar space.