Extending Galactic Habitable Zone Modeling to Include the Emergence of Intelligent Life

Abstract

Previous studies of the galactic habitable zone have been concerned with identifying those regions of the Galaxy that may favor the emergence of complex life. A planet is deemed habitable if it meets a set of assumed criteria for supporting the emergence of such complex life. In this work, we extend the assessment of habitability to consider the potential for life to further evolve to the point of intelligence--termed the propensity for the emergence of intelligent life, φI. We assume φI is strongly influenced by the time durations available for evolutionary processes to proceed undisturbed by the sterilizing effects of nearby supernovae. The times between supernova events provide windows of opportunity for the evolution of intelligence. We developed a model that allows us to analyze these window times to generate a metric for φI, and we examine here the spatial and temporal variation of this metric. Even under the assumption that long time durations are required between sterilizations to allow for the emergence of intelligence, our model suggests that the inner Galaxy provides the greatest number of opportunities for intelligence to arise. This is due to the substantially higher number density of habitable planets in this region, which outweighs the effects of a higher supernova rate in the region. Our model also shows that φI is increasing with time. Intelligent life emerged at approximately the present time at Earth's galactocentric radius, but a similar level of evolutionary opportunity was available in the inner Galaxy more than 2 Gyr ago. Our findings suggest that the inner Galaxy should logically be a prime target region for searches for extraterrestrial intelligence and that any civilizations that may have emerged there are potentially much older than our own.

‘Grandeur in this view of life’:N-body simulation models of the Galactic habitable zone

“…The present model results are in discrepancy with the studies of Gowanlock, Patton & McConnell (2011) and Morrison & Gowanlock (2015), who obtain much more centrally concentrated GHZ. While the exact reasons will require a separate study to ascertain, we find that one or more of the following played an important part in creating the discrepancy: (i) the model of Gowanlock, Patton & McConnell (2011) applies specifically to the Milky Way, and uses a semi-analytic stellar density and star-formation history models specifically geared toward the local observations.…”

Relative Likelihood of Success in the Search for Primitive versus Intelligent Extraterrestrial Life

“…11 Another possible phenomenon that can raise the value of α is panspermia (Arrhenius, 1908;Wickramasinghe, 2010), which is expected to be particularly effective in certain astrophysical environments such as globular clusters (Di Stefano and Ray, 2016), the Galactic centre (Morrison and Gowanlock, 2015;Chen et al, 2018), and M-dwarfs (Lingam and Loeb, 2017a).…”

Stellar encounters with giant molecular clouds

“…Additionally, authors argue (Gonzalez et al 2001;Vukotić et al 2016) that the high metallicity will make terrestrial planets with such high surface densities as to be inhospitable for organic life. Another way of setting the bound is by looking at the hazards posed by the Galaxy, primarily nearby supernovae (Gowanlock et al 2011;Spitoni et al 2014;Morrison & Gowanlock 2015).…”

“…Carrera et al (2016) that a high multiplicity of gas giants cause problems for habitable systems as they destabilize the system. The other way of determining the boundary is to look at supernova rates (Gowanlock et al 2011;Spitoni et al 2014;Morrison & Gowanlock 2015), and then calculate how often a star would experience a nearby supernova. One then sets a threshold for the acceptable supernova rate (usually a factor of the nearby Solar supernova rate) and find the boundary.…”