Regular black hole motion and stellar orbital resonances |
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Authors: | C M Boily T Padmanabhan A Paiement |
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Institution: | Observatoire astronomique &CNRS UMR 7550, Universitéde Strasbourg I, 11 rue de l'université, F-67000 Strasbourg, France;IUCAA, Ganeshkhind Post Bag 4, Pune, India;ENSP de Strasbourg, Parc d'innovation, Bd. Sébastien Brant BP 10413, F-67412 Illkirch, France |
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Abstract: | The motion of a black hole about the centre of gravity of its host galaxy induces a strong response from the surrounding stellar population. We treat the case of a harmonic potential analytically and show that half of the stars on circular orbits in that potential shift to an orbit of lower energy, while the other half receive a positive boost and recede to a larger radius. The black hole itself remains on an orbit of fixed amplitude and merely acts as a catalyst for the evolution of the stellar energy distribution function f ( E ). We show that this effect is operative out to a radius of approximately three to four times the hole's influence radius, R bh. We use numerical integration to explore more fully the response of a stellar distribution to black hole motion. We consider orbits in a logarithmic potential and compare the response of stars on circular orbits, to the situation of a 'warm' and 'hot' (isotropic) stellar velocity field. While features seen in density maps are now wiped out, the kinematic signature of black hole motion still imprints the stellar line-of-sight mean velocity to a magnitude ?13 per cent the local rms velocity dispersion σ. A study in three dimensions suggests a reduced effect for polar orbits. |
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Keywords: | gravitation stellar dynamics Galaxy: centre galaxies: nuclei |
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