TY - JOUR

T1 - Thawing the frozen-in approximation

T2 - Implications for self-gravity in deeply plunging tidal disruption events

AU - Steinberg, Elad

AU - Coughlin, Eric R.

AU - Stone, Nicholas C.

AU - Metzger, Brian D.

N1 - Funding Information:
ES and BDM are supported in part by the National Science Foundation (grant number AST-1615084) and the NASA Fermi Guest Investigator Program (grant number 80NSSC18K1708). ERC acknowledges support from NASA through the Einstein Fellowship Program, Grant PF6-170170. NCS and BDM are supported in part by the NASA Astrophysics Theory Program (grant number NNX17AK43G).

PY - 2019/5/1

Y1 - 2019/5/1

N2 - The tidal destruction of a star by a massive black hole, known as a tidal disruption event (TDE), is commonly modelled using the 'frozen-in' approximation. Under this approximation, the star maintains exact hydrostatic balance prior to entering the tidal sphere (radius rt), after which point its internal pressure and self-gravity become instantaneously negligible and the debris undergoes ballistic free fall. We present a suite of hydrodynamical simulations of TDEs with high penetration factors β rt/rp = 5-7, where rp is the pericentre of the stellar centre of mass, calculated using a Voronoi-based moving-mesh technique. We show that basic assumptions of the frozen-in model, such as the neglect of self-gravity inside rt, are violated. Indeed, roughly equal fractions of the final energy spread accumulate exiting and entering the tidal sphere, though the frozen-in prediction is correct at the order-of-magnitude level. We also show that an $\mathcal {O}(1)$ fraction of the debris mass remains transversely confined by self-gravity even for large β which has implications for the radio emission from the unbound debris and, potentially, for the circularization efficiency of the bound streams.

AB - The tidal destruction of a star by a massive black hole, known as a tidal disruption event (TDE), is commonly modelled using the 'frozen-in' approximation. Under this approximation, the star maintains exact hydrostatic balance prior to entering the tidal sphere (radius rt), after which point its internal pressure and self-gravity become instantaneously negligible and the debris undergoes ballistic free fall. We present a suite of hydrodynamical simulations of TDEs with high penetration factors β rt/rp = 5-7, where rp is the pericentre of the stellar centre of mass, calculated using a Voronoi-based moving-mesh technique. We show that basic assumptions of the frozen-in model, such as the neglect of self-gravity inside rt, are violated. Indeed, roughly equal fractions of the final energy spread accumulate exiting and entering the tidal sphere, though the frozen-in prediction is correct at the order-of-magnitude level. We also show that an $\mathcal {O}(1)$ fraction of the debris mass remains transversely confined by self-gravity even for large β which has implications for the radio emission from the unbound debris and, potentially, for the circularization efficiency of the bound streams.

KW - black hole physics

KW - galaxies: nuclei

KW - hydrodynamics

KW - methods: numerical

KW - stars: kinematics and dynamics

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U2 - 10.1093/mnrasl/slz048

DO - 10.1093/mnrasl/slz048

M3 - Article

AN - SCOPUS:85079456567

VL - 485

SP - L146-L150

JO - Monthly Notices of the Royal Astronomical Society: Letters

JF - Monthly Notices of the Royal Astronomical Society: Letters

SN - 1745-3925

IS - 1

ER -