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Title: Dynamical friction on star clusters : implications for the galactic centre
Author: Petts, James A.
ISNI:       0000 0004 6494 5724
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2017
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I present a new semi-analytic dynamical friction model built upon Chandrasekhar's formalism (Petts et al., 2015, 2016), and its first scientific application regarding the origin of the young stellar populations in the Galactic Centre (Petts and Gualandris, 2017). The model is accurate for spherical potentials of varying inner slope, gamma=[0,2], due to a few key novelties. Firstly, I use physically motivated, radially varying maximum and minimum impact parameters, that describe the range over which interactions are important. Secondly, I use the self-consistent velocity distribution as derived from the distribution function of the galactic potential, including the effect of stars moving faster than satellite. Finally, I reproduce the core-stalling effect seen in simulations of cored galaxies with a ``tidal-stalling'' prescription, which describes when the satellite disrupts the galaxy and forms a steady-state. I implemented dynamical friction analytically in the direct summation N-body code, NBODY6, excellently reproducing the orbital decay of clusters as compared with full N-body models. Since only cluster stars need be modelled in an N-body fashion, my method allows for simulation possibilities that were previously prohibited (e.g. Contenta et al., 2017; Inoue, 2017; Cole et al., 2017). Using this new method, I explore the scenario in which the young stellar populations in the central parsec of the Milky Way were formed by infalling star clusters. I find that clusters massive enough to reach the central parsec within the lifetime of these populations form very massive stars via collisions. Using up to date - yet conservative - mass loss recipes, I find that these very massive stars lose most of their mass via strong stellar winds, forming large stellar mass black holes incapable of bringing stars to the central parsec. A star cluster infalling in the Galactic Centre within the last 15 Myr would leave an observable population of massive stars from ~1-10 pc, contradicting observations. Thus, I rule out the star cluster inspiral scenario, favouring in-situ formation and/or binary disruption for the origin of the young stars.
Supervisor: Gualandris, Alessia ; Gieles, Mark Sponsor: Department of Physics, University of Surrey
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available