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The First Stars and Galaxies: Challenges for the Next Decade Participants
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Talk
Title: Disc Fragmentation around Primordial Stars Author(s): Paul Clark Abstract: The formation of the first stars in dark matter minihalos has been well studied, and we now have models than can follow the evolution of the baryons to protostellar densities (e.g. Yoshida et al 2008). In our present study we shift our focus to somewhat lower densities, aiming to capture the evolution of the infalling gas over several thousand years. Using sink particles, we can replace the gravitationally bound gas at densities higher than 10$^{15}$ cm${-3}$ and radii greater than 4 AU from the central protostellar core, with an accreting point mass that is able to gravitationally interact with the surrounding gas. This enables us to capture the formation of the discs around primordial stars for the first time. We study in detail the early stages of the subsequent disc buildup, showing that, after several hundred years, the disc becomes gravitationally unstable. Furthermore, it becomes sufficiently extended that the cooling time is eventually shorter than the orbital period, such that the `Gammie Criteria' are satisfied and the disc can fragment. Although our current calculations are unable to capture the effects of the accretion luminosity from the central core, we show that this cannot significantly alter the heat balance in the regions of the disc where fragmentation takes place. We therefore predict that the first stars in the universe are binaries.
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