The best place and time to live in the Milky Way

Abstract

Context. Counted 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 from terrestrial planets (TPs). Nearby high-energy transient astrophysical events have been proposed as possible triggers of mass extinctions on Earth. Aims. We assess the habitability of the Milky Way (MW) throughout its cosmic history against potentially disruptive astrophysical transients with the aim of identifying the safest places and epochs within our Galaxy. We also test the hypothesis that one long GRB played a leading role in the late Ordovician mass-extinction event (∼445 Myr ago). Methods. We characterised the habitability of the MW throughout its cosmic history as a function of galactocentric distance of TPs. We estimated the dangerous effects of transient astrophysical events (long and short GRBs and SNe) with a model that connects their rate to the specific star formation and metallicity evolution within the Galaxy throughout its cosmic history. Our model also accounts for the probability that TPs form around FGK and M stars. Results. Until about six billion years ago, the outskirts of the Galaxy were the safest places to live, despite the relatively low density of TPs. In the last about four billion years, regions between 2 and 8 kpc from the center, which had a higher density of TPs, became the best places for a relatively safer biotic life growth. We confirm the hypothesis that one long GRB played a leading role in the late Ordovician mass-extinction event. In the last 500 Myr, the safest neighborhood in the Galaxy was a region at a distance of 2 to 8 kpc from the Galactic center, whereas the MW outskirts were sterilized by two to five long GRBs.

If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare

“…A literature on a galactic habitable zone tries to estimate star habitability as a function of galactic position and time, in part by considering rates of nearby sterilizing explosions such as supernovae and gamma-ray bursts (Ward & Brownlee 2000;Gonzalez et al 2001;Lineweaver et al 2004;Vukotic & Cirkovic 2007;Prantzos 2008;Vukotic 2010;Gowanlock et al 2011;Legassick 2015;Morrison & Gowanlock 2015;Forgan et al 2017;Cai et al 2021;Spinelli et al 2021). While such explosions are much less damaging to simpler life (Sloan et al 2017), in this paper we accept the usual assumption of no panspermia, and thus require habitable planets to support complex life, which is more fragile.…”

“…Our grabby alien model can explain a striking empirical puzzle: why have we humans appeared so early in the universe? Yes, many calculations often find our date to be not greatly atypical of habitable durations undisturbed by nearby sterilizing explosions, for both short and long durations (Ward & Brownlee 2000;Gonzalez et al 2001;Lineweaver et al 2004;Vukotic & Cirkovic 2007;Prantzos 2008;Vukotic 2010;Gowanlock et al 2011;Legassick 2015;Morrison & Gowanlock 2015;Forgan et al 2017;Cai et al 2021;Spinelli et al 2021). Other calculations find us to be early, even if not extremely early, when planets at many lower mass stars are considered habitable (Gale & Wandel 2017;Haqq-Misra et al 2018;Wandel & Gale 2020).…”

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. Spinelli et al (2020) 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.…”

The impact of AGN outflows on the surface habitability of terrestrial planets in the Milky Way

“…Moreover, it is important to recognise that analyses of the effects of central black hole activity on habitability are not merely interesting in their own right but also because they can be selfconsistently incorporated into state-of-the-art numerical simulations of galactic habitability (Dayal et al 2015;Gobat & Hong 2016;Vukotić et al 2016;Forgan et al 2017;Spitoni et al 2017;Stanway et al 2018;Jošović et al 2019;Stojković et al 2019;Spinelli et al 2021) -which have built on earlier works (e.g., Gonzalez et al 2001;Lineweaver et al 2004) -and include high-energy phenomena such as supernovae or gamma-ray bursts. These statistical models enable us to trace how the habitability of the Universe as a whole has evolved with cosmic time.…”