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Hyperaccretion during tidal disruption events: weakly bound debris envelopes and jets
After the destruction of the star during a tidal disruption event (TDE), the
cataclysmic encounter between a star and the supermassive black hole (SMBH) of
a galaxy, approximately half of the original stellar debris falls back onto the
hole at a rate that can initially exceed the Eddington limit by orders of
magnitude. We argue that the angular momentum of this matter is too low to
allow it to attain a disk-like configuration with accretion proceeding at a
mildly super-Eddington rate, the excess energy being carried away by a
combination of radiative losses and radially distributed winds. Instead, we
propose that the infalling gas traps accretion energy until it inflates into a
weakly-bound, quasi-spherical structure with gas extending nearly to the poles.
We study the structure and evolution of such "Zero-Bernoulli accretion" flows
(ZEBRAs) as a model for the super-Eddington phase of TDEs. We argue that such
flows cannot stop extremely super-Eddington accretion from occurring, and that
once the envelope is maximally inflated, any excess accretion energy escapes
through the poles in the form of powerful jets. We compare the predictions of
our model to Swift J1644+57, the putative super-Eddington TDE, and show that it
can qualitatively reproduce some of its observed features. Similar models,
including self-gravity, could be applicable to gamma-ray bursts from collapsars
and the growth of supermassive black hole seeds inside quasi-stars.Comment: 19 pages, 14 figures. Accepted for publication in Ap
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