# Thawing the frozen-in approximation: Implications for self-gravity in deeply plunging tidal disruption events

Elad Steinberg, Eric R. Coughlin, Nicholas C. Stone, Brian D. Metzger

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

## Abstract

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.

Original language English (US) L146-L150 Monthly Notices of the Royal Astronomical Society: Letters 485 1 https://doi.org/10.1093/mnrasl/slz048 Published - May 1 2019 Yes

## Keywords

• black hole physics
• galaxies: nuclei
• hydrodynamics
• methods: numerical
• stars: kinematics and dynamics

## ASJC Scopus subject areas

• Astronomy and Astrophysics
• Space and Planetary Science

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