Abstract
What makes a planet habitable? This is quite a complex question to approach, and one that does not have anything that resembles a simple answer. Is it the proximity of a planet to its host star? How massive a planet is, where habitability is limited by surface gravity? Perhaps it comes down to a combination of all these factors and more. An obvious place to start answering this question is to look for what is familiar. The streetlight effect or the drunkard’s search principle refers to this idea, specifically the observational bias of looking where it is familiar or easiest to look. Venturing no further than the Earth gives us a benchmark on which to base habitability, and perhaps the most striking feature when looking at the Earth is the vast abundance of water. As there is yet any evidence to the contrary, water is an essential requirement for the presence of life. Although rocky exoplanets have been discovered in high abundance already, some even with water spectral lines, the challenge remains to discover when the earliest time and in what conditions the first of these worlds formed. The epoch of first metal enrichment presents an obvious place to start looking. Population III supernovae out of the first generation of massive stars were the first great nucleosynthetic engines in the Universe, forging the first metals within their cores that exploded and disseminated their contents throughout the interstellar medium. The introduction of metals into the Universe had huge implications for the continued chemo-thermal evolution of a system. In this thesis, we will employ a variety of methods to approach this question. We start by simulating the collapse of primordial minihaloes in the mass regime of 105 M⊙ of dark matter at redshift 20, firstly using the built-in Enzo hydrodynamical simulation code chemical solver, and then extending this to the well-known astrochemical solver KROME. Initially, we limit the chemical species to the 12-species primordial model, beforeusing KROME to extend this to carbon, oxygen, and silicon-bearing species.
We also present 3 hydrodynamical cosmological simulations using the Grackle chem- istry solver within Enzo where we test various configurations of Population III progenitor masses (13 M⊙ and 200 M⊙) and host halo masses (105 M⊙, 106 M⊙, and 107 M⊙). We find that the mass of the host halo plays a significant role in the ability of metal ejecta to collect and collapse in significant quantities to trigger water formation. The metals released by the explosion are expelled from the core as the HII region breaks out within the Pop III star’s main sequence lifetime due to the low mass of the minihalo. Additionally, these metals are unable to mix into the nearby dense clump that falls into the central region shortly after the explosion. Moreover, in the remnant of a 13 M⊙ CCSN (Core-Collapse Supernova), we see the collapse of a dense, wet, and dusty cloud. This metal-enriched cloud (Z = 1 × 10−4 Z⊙) reaches densities of nH > 108 cm−3 and a peak water abundance of yH O = 3.05 × 10−8, suggesting the possibility of the for- mation of a protoplanetary disc and a second generation protostar at this location. If these circumstances can result in the formation of a wet, rocky planet, further research using specialised planetary formation codes will help confirm this.
We conclude with a simulation that attempts to probe the largest Population III progenitor masses and supernovae energies with a 200 M⊙ PISN (Pair-Instability Su- pernova) in a 107 M⊙ halo. At the time of simulation conclusion, we are unable to make any claims about water formation, however, we can speculate that the vast quantity of metals ejected may provide the best opportunity for water formation and the collapse of a system with a significant water abundance.
| Date of Award | 26 May 2023 |
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| Original language | English |
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| Supervisor | Daniel Whalen (Supervisor), Daniel Thomas (Supervisor) & Claudia Maraston (Supervisor) |