The Tidal Disruption of Sun-like Stars by Massive Black Holes

Abstract

We present the first simulations of the tidal disruption of stars with realistic structures and compositions by massive black holes (BHs). We build stars in the stellar evolution code MESA and simulate their disruption in the 3D adaptive-mesh hydrodynamics code FLASH, using an extended Helmholtz equation of state and tracking 49 elements. We study the disruption of a 1M star and 3M star at zero-age main sequence (ZAMS), middle-age, and terminal-age main sequence (TAMS). The maximum BH mass for tidal disruption increases by a factor of ∼2 from stellar radius changes due to MS evolution; this is equivalent to varying BH spin from 0 to 0.75. The shape of the mass fallback rate curves is different from the results for polytropes of Guillochon & Ramirez-Ruiz (2013). The peak timescale t peak increases with stellar age, while the peak fallback rateṀ peak decreases with age, and these effects diminish with increasing impact parameter β. For a β = 1 disruption of a 1M star by a 10 6 M BH, from ZAMS to TAMS, t peak increases from 30 to 54 days, whileṀ peak decreases from 0.66 to 0.14 M /yr. Compositional anomalies in nitrogen, helium, and carbon can occur before the peak timescale for disruptions of MS stars, which is in contrast to predictions from the "frozen-in" model. More massive stars can show stronger anomalies at earlier times, meaning that compositional constraints can be key in determining the mass of the disrupted star. The abundance anomalies predicted by these simulations provide a natural explanation for the spectral features and varying line strengths observed in tidal disruption events.

The Art of Modeling Stellar Mergers and the Case of the B[e] Supergiant R4 in the Small Magellanic Cloud

“…To conclude, the proposed numerical formalism may be applied to model the outcomes of mergers, collisions, and tidal disruptions (Law-Smith et al 2019. On the timescale of the study, we could only hope to explore in detail merely some subset of the interesting possible encounters that could have given rise to the R4 system (Figure 1).…”

“…Our setup is adapted from Guillochon & Ramirez-Ruiz (2013), but it uses an extended Helmholtz equation of state (Timmes & Swesty 2000) instead of a polytropic equation of state. In addition, we track the composition of elements as described in Law-Smith et al (2019).…”

Simulations of Tidal Disruption Events

“…Care should be taken in this context only for very deeply penetrating events, for which relativistic effects and thermonuclear detonation (for white dwarfs disruption) could play an important role. As a result, most of the numerical work done in this context, rather than improving the numerics, is aimed at including progressively more complex geometries, for example exploring disruption by binary black holes Vigneron et al 2018) or the role of stellar spin (Golightly et al 2019a;Sacchi and Lodato 2019), or that of realistic stellar structure (Law-Smith et al 2019).…”

“…If the local simulation follows the debris to this point, then an estimate of the return rate of debris to the black hole can be derived from the numerical results . While the star is typically modeled as a polytrope given by a single adiabatic index, the use of stellar profiles derived from the open source code MESA, Modules for Experiments in Stellar Astrophysics, enables a study of the effects of tidal disruptions on stellar cores and tidal stripping of stellar envelopes (MacLeod et al 2012(MacLeod et al , 2013Law-Smith et al 2017;Anninos et al 2018;Law-Smith et al 2019;Goicovic et al 2019). It is interesting to note that for some partial disruptions, the remnant core receives a "kick" into an unbound orbit (Manukian et al 2013).…”

What causes the fragmentation of debris streams in TDEs?

“…The actual lightcurve of TDEs will depend on several other physical effects. The internal structure of the star may modify the long term evolution of the stream (Lodato et al 2009;Guillochon & Ramirez-Ruiz 2013;Law-Smith et al 2019;Ryu et al 2020). The possible influence of a secondary black hole (Liu et al 2009;Coughlin et al 2017;Coughlin & Armitage 2018;Vigneron et al 2018; will affect the orbital evolution of the debris.…”