Asymmetrical thermonuclear supernovae triggered by the tidal disruption of white dwarfs

¹ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St George St, Toronto, ON, M5S 3H8, Canada
² Institut d’Astrophysique de Paris, CNRS-Sorbonne Université, 98 bis boulevard Arago, F-75014, Paris, France
³ JILA, University of Colorado and National Institute of Standards and Technology, 440 UCB, Boulder, 80308, CO, USA
⁴ Department of Astrophysical and Planetary Sciences, 391 UCB, Boulder, 80309, CO, USA
⁵ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85748, Garching bei München, Germany

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 28 January 2026
Accepted: 30 March 2026

Abstract

In a dense star cluster core, a tidal disruption event (TDE) of a white dwarf (WD) can occur if the WD passes within the tidal radius of an intermediate-mass black hole (IMBH). Very close encounters cause extreme tidal compression in the WD, raising temperatures enough to induce runaway fusion and produce a thermonuclear supernova (SN). Using the hydrodynamics code AREPO augmented with a 55-isotope nuclear reaction network, we performed high-resolution simulations of the TDE of a 0.6 M_⊙ C/O WD by a 500 M_⊙ IMBH for different values of the scaled impact parameter b (i.e., the ratio of periapsis distance to tidal radius). Closer encounters produce combined TDE+SN events, with a partial burning of ¹²C and ¹⁶O into heavier isotopes – the ⁵⁶Ni fractions of the disrupted WD material vary from 1% at b = 0.19 to 82% at b = 0.10, while wider ones (b ≳ 0.20) lead to standard TDEs. In all cases, the material away from the denser regions remains unburnt, spanning a wide range of radial velocities. Such WD TDEs also exhibit a central cavity, wherein little material is found below a radial velocity of several 1000 km s⁻¹. We also performed 1D and 2D radiative-transfer calculations for these WD-TDEs using the codes CMFGEN and LONG_POL, respectively, covering epochs from a few days to one hundred days. We recover the typical rise times and peak luminosities of SNe Ia, but with an extremely strong viewing-angle dependence of both light curves and spectra. At nebular times, isolated strong emission lines such as [Ca II] λλ 7291,  7323 may appear both displaced and skewed by many 1000 km s⁻¹ – such extreme offsets are harder to identify at earlier times due to optical depth effects and line overlap. WD TDEs may produce a diverse set of transients with extreme asymmetry and peculiar composition.