Evolution of galaxy habitability

TL;DR

This study combines galaxy evolution models with habitable zone data to assess how galaxy properties influence the potential for habitable planets over cosmic time, finding that habitability varies weakly with galaxy mass and has remained relatively stable for the last 8 billion years.

Contribution

It introduces a novel integration of galaxy evolution and planetary habitability models to evaluate how galaxy characteristics affect habitable planet occurrence and evolution.

Findings

Habitability peaks at galaxy mass ~4e10 Msun.

Approximately 0.7% of stars in Milky Way-like galaxies host habitable planets.

Most habitable planets in local galaxies formed about 1.5 Gyr before Earth.

Abstract

We combine a semi-analytic model of galaxy evolution with constraints on circumstellar habitable zones and the distribution of terrestrial planets to probe the suitability of galaxies of different mass and type to host habitable planets, and how it evolves with time. We find that the fraction of stars with terrestrial planets in their habitable zone (known as habitability) depends only weakly on galaxy mass, with a maximum around 4e10 Msun. We estimate that 0.7% of all stars in Milky Way type galaxies to host a terrestrial planet within their habitable zone, consistent with the value derived from Kepler observations. On the other hand, the habitability of passive galaxies is slightly but systematically higher, unless we assume an unrealistically high sensitivity of planets to supernovae. We find that the overall habitability of galaxies has not changed significantly in the last ~8 Gyr, with most of the habitable planets in local disk galaxies having formed ~1.5 Gyr before our own solar system. Finally, we expect that ~1.4e9 planets similar to present-day Earth have existed so far in our galaxy.