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

41 Scopus citations


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 languageEnglish (US)
Pages (from-to)L146-L150
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
StatePublished - May 1 2019
Externally publishedYes


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

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Thawing the frozen-in approximation: Implications for self-gravity in deeply plunging tidal disruption events'. Together they form a unique fingerprint.

Cite this