The best place and time to live in the Milky Way

Abstract

Context. Among the most powerful cosmic events, supernovae (SNe) and γ´ray bursts (GRBs) can be highly disruptive for life: their radiation can be harmful for biota or induce extinction by removing most of the protective atmospheric ozone layer on terrestrial planets. Nearby high-energy transient astrophysical events have been proposed as possible triggers of mass extinctions on Earth. Aims. We aim at assessing the habitability of the Milky Way (MW) along its cosmic history against potentially disruptive astrophysical transients with the scope of identifying the safest places and epochs within our Galaxy. We also test the hypothesis that long GRBs had a leading role in the late Ordovician mass extinction event (" 440 Myrs ago). Methods. We characterise the habitability of the MW along its cosmic history as a function of galactocentric distance of terrestrial planets. We estimate the dangerous effects of transient astrophysical events (long/short GRBs and SNe) with a model which binds their rate to the specific star formation and metallicity evolution within the Galaxy along its cosmic history. Our model also accounts for the probability of forming terrestrial planets around FGK and M stars. Results. Until "6 billion years ago the outskirts of the Galaxy were the safest places to live, despite the relatively low density of terrestrial planets. In the last "4 billion years, regions between 2 and 8 kpc from the center, featuring a higher density of terrestrial planets, became the best places for a relatively safer biotic life growth. We confirm the hypothesis that one long GRB had a leading role in the late Ordovician mass extinction event. In the last 500 Myrs, the safest galactic region is comprised between 2 and 8 kpc from the center of the MW, whereas the outskirts of the Galaxy have been sterilized by 2-5 long GRBs.

Dynamics of the spiral-arm corotation and its observable footprints in the Solar Neighborhood

“…Still another approach is to map the regions of the Galactic disk where powerful cosmic events, like supernovae and γ-ray bursts, able to destroy the life of Terrestrial Planets, have larger or smaller probability to take place. [129] compute the rate of the events as being proportional to star formation rate and metallicity. They use an axisymmetric model for these parameters, ignoring the spiral arms.…”