James Guillochon, Haik Manukian, Enrico Ramirez-Ruiz
When a star comes within a critical distance to a supermassive black hole (SMBH), immense tidal forces can remove a significant fraction of the star's mass, resulting in a stream of debris that falls back onto the black hole and powers a luminous flare. In this paper, we perform two hydrodynamical simulations of the disruption of a main-sequence star by a SMBH to characterize the evolution of the debris stream after a tidal disruption. We demonstrate that this debris stream is confined by self-gravity in the two directions perpendicular to the original direction of the star's travel, restricting its width and height to be only a factor of a few larger than its original size. As a consequence, the stream has a negligible surface area and makes almost no contribution to either the continuum or line emission. We propose that any observed emission lines are not the result of photoionization in the unbound debris, but are produced in the region above and below the forming elliptical accretion disk, the same region in which the broad-line region is expected to be produced in steadily-accreting active galactic nuclei. As each line within a broad-line region is observationally linked to a particular location in the accretion disk, we suggest that the absence of a line indicates that the accretion disk does not yet extend to the distance required to produce that line. This model can be used to understand the spectral properties of the tidal disruption event PS1-10jh, for which HeII lines are observed, but the Balmer series and HeI are not. Using a maximum likelihood analysis, we go on to show that a partial disruption of a main-sequence star of near-solar composition can reproduce this event. [abridged]
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http://arxiv.org/abs/1304.6397
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