Formation of Supermassive Black Hole Seeds in the First Galaxies
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AbstractFrontier observations of quasars at redshifts z > 6 suggest the existence of supermassive black holes of masses 1,000,000,000 solar masses when the Universe was less than a billion years old. These objects most likely grew from smaller black hole seeds, although the origin of these seeds still remains unclear. We investigate the process of formation and evolution of supermassive black hole seeds in the first galaxies. First, we perform the highest-resolution hydrodynamical simulation to date to analyze the formation of a supermassive protostar of 0.1 solar masses at the center of an atomic cooling halo. We show that, although the gas fragments and forms a protostellar system, the system still accretes mass at rates high enough to become a massive black hole seed within a few hundred thousand years. Unfortunately, due to the high resolution achieved, these simulations become prohibitively expensive after 20 years and we are not able to follow its development at later times. Instead, we describe the subsequent evolution using analytical methods and a one-zone model. We deduce a mass-radius relation for the growth of the protostar and utilize such relation to derive a sub-grid recipe for the accretion radius of sink particles in numerical simulations. Then, we use this sub-grid model in cosmological simulations where the maximum resolution has been limited in order to follow the growth of the protostar for a longer time. We present a suite of six simulations using three different thresholds for the resolution and two methods to model the central object. Using this approach, we describe the early, intermediate, and late stages of the buildup of black hole seeds, from its formation as a massive protostar of 10 solar masses and until it becomes a massive black hole seed of 100,000 solar masses. Finally, we complement this picture by adding the effect of radiative feedback from the central source in the surrounding gas. We outline the implementation of the radiative transfer equations in our hydrodynamical simulations and show preliminary results of our calculations. Fully coupled radiation-hydrodynamical simulations will give us a complete description of the assembly of supermassive black hole seeds in the early Universe.
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