The quest for cradles of life: using the fundamental metallicity relation to hunt for the most habitable type of galaxy

TL;DR

This paper introduces a cosmobiological framework utilizing the fundamental metallicity relation to identify the most habitable galaxy types, revealing that massive elliptical galaxies may host vastly more habitable planets than the Milky Way.

Contribution

It develops a novel method linking galaxy properties through the fundamental metallicity relation to assess galactic habitability on a large scale.

Findings

Massive elliptical galaxies can host up to 10,000 times more habitable planets than the Milky Way.

Metal-rich, large elliptical galaxies are the most probable cradles of life in the universe.

Galactic habitability correlates strongly with the fundamental metallicity relation.

Abstract

The field of astrobiology has made huge strides in understanding the habitable zones around stars (Stellar Habitable Zones) where life can begin, sustain its existence and evolve into complex forms. A few studies have extended this idea by modelling galactic-scale habitable zones (Galactic Habitable Zones) for our Milky Way and specific elliptical galaxies. However, estimating the habitability for galaxies spanning a wide range of physical properties has so far remained an outstanding issue. Here, we present a "cosmobiological" framework that allows us to sift through the entire galaxy population in the local Universe and answer the question "Which type of galaxy is most likely to host complex life in the cosmos"? Interestingly, the three key astrophysical criteria governing habitability (total mass in stars, total metal mass and ongoing star formation rate) are found to be intricately linked through the "fundamental metallicity relation" as shown by SDSS (Sloan Digital Sky Survey) observations of more than a hundred thousand galaxies in the local Universe. Using this relation we show that metal-rich, shapeless giant elliptical galaxies at least twice as massive as the Milky Way (with a tenth of its star formation rate) can potentially host ten thousand times as many habitable (earth-like) planets, making them the most probable "cradles of life" in the Universe.