A tidal disruption event occurs when a star wanders close enough to a black hole to be disrupted by its tidal force. The debris of a tidally disrupted star are expected to form an accretion disc around the supermassive black hole. The light curves of these events sometimes show a quasi-periodic modulation of the flux that can be associated with the precession of the accretion disc due to the Lense-Thirring ('frame-dragging') effect. Since the initial star orbit is in general inclined with respect to the black hole spin, this misalignment combined with the Lense-Thirring effect leads to a warp in the disc. In this paper, we provide a simple model of the system composed by a thick and narrow accretion disc surrounding a spinning supermassive black hole, with the aim to: (a) compute the expected precession period as a function of the system parameters, (b) discuss the conditions that have to be satisfied in order to have rigid precession, (c) investigate the alignment process, highlighting how different mechanisms play a role leading the disc and the black hole angular momenta into alignment.
Franchini, A., Lodato, G., Facchini, S. (2016). Lense-Thirring precession around supermassive black holes during tidal disruption events. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 455(2), 1946-1956 [10.1093/mnras/stv2417].
Lense-Thirring precession around supermassive black holes during tidal disruption events
Franchini A.
;
2016
Abstract
A tidal disruption event occurs when a star wanders close enough to a black hole to be disrupted by its tidal force. The debris of a tidally disrupted star are expected to form an accretion disc around the supermassive black hole. The light curves of these events sometimes show a quasi-periodic modulation of the flux that can be associated with the precession of the accretion disc due to the Lense-Thirring ('frame-dragging') effect. Since the initial star orbit is in general inclined with respect to the black hole spin, this misalignment combined with the Lense-Thirring effect leads to a warp in the disc. In this paper, we provide a simple model of the system composed by a thick and narrow accretion disc surrounding a spinning supermassive black hole, with the aim to: (a) compute the expected precession period as a function of the system parameters, (b) discuss the conditions that have to be satisfied in order to have rigid precession, (c) investigate the alignment process, highlighting how different mechanisms play a role leading the disc and the black hole angular momenta into alignment.File | Dimensione | Formato | |
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