Life in Elliptical Galaxies: Hot Spheroids, Fast Stars, Deadly Comets?

TL;DR

Elliptical galaxies' hot stellar populations lead to high-velocity minor bodies, causing frequent impacts that may limit the development of intelligent life within their central regions.

Contribution

This study estimates impact rates of minor bodies in elliptical galaxies and explores their implications for habitability and intelligent life evolution.

Findings

Impact rates are generally low (~0.01-0.1 Gyr$^{-1}$) in most elliptical galaxies.

Certain compact galaxies have impact rates exceeding 10 Gyr$^{-1}$, potentially hindering life.

An exclusion zone of about 100 parsecs around galaxy centers may prevent life development.

Abstract

Elliptical galaxies have dynamically hot ($\sigma_{1D}$ ~ 100 -- 300 km s$^{-1}$) populations of stars, and presumably, smaller objects like comets. Because interstellar minor bodies are moving much faster, they hit planets harder and more often than in the local Galaxy. I estimate the rates for Chicxulub-scale impacts on an Earth-size planet in elliptical galaxies as a potential habitability constraint on intelligent life. Around most stars in a normal elliptical galaxy, these planets receive only ~0.01 -- 0.1 Gyr$^{-1}$, although hazardous rates may be common in certain compact early-type galaxies and red nuggets. About 5% of the stellar mass is in a region where the rate is >10 Gyr$^{-1}$, large enough to dominate the mass extinction rate. This suggests that elliptical galaxies have an exclusion zone of order one hundred parsecs in radius around their centers for the evolution of intelligent life.