[Paper Review] Type Ia Supernovae Can Arise from the Detonations of Both Stars in a Double Degenerate Binary

Samuel J. Boos, Dean M. Townsley+1 more|arXiv (Cornell University)|Jan 15, 2024

Gamma-ray bursts and supernovae4 citations

TL;DR

This paper presents 2D hydrodynamic simulations showing that Type Ia supernovae can result from sequential detonations in a double degenerate binary, where the primary white dwarf undergoes a double detonation that triggers a secondary detonation in the companion. Synthetic light curves and spectra from these triple- and quadruple-detonation scenarios match observed SNe Ia as well as isolated double detonation models, despite drastically different ejecta masses and elemental yields.

ABSTRACT

The precise origin of Type Ia supernovae (SNe Ia) is unknown despite their value to numerous areas in astronomy. While it is a long-standing consensus that they arise from an explosion of a carbon/oxygen white dwarf, the exact progenitor configurations and explosion mechanisms that lead to SNe Ia are still debated. One popular theory is the double detonation in which a helium layer, accreted from a binary companion, detonates on the surface of the primary star, leading to a converging shock-induced detonation of the underlying core. It has recently been seen in simulations that a helium-rich degenerate companion may undergo its own explosion triggered by the impact from the ejecta of the primary star. We show 2D simulations that approximate a white dwarf undergoing a double detonation which triggers the explosion of the degenerate companion, leading to either a triple or quadruple detonation. We also present the first multi-dimensional radiative transfer results from the triple and quadruple detonation scenario. We find that within a range of mass configurations of the degenerate binary, the synthetic light curves and spectra of these events match observations as well as theoretical models of isolated double detonations do. Notably, double and quadruple detonations that are spectrally similar and reach the same peak brightnesses have drastically different ejection masses and produce different amounts of Si- and Fe-group elements. Further understanding of this scenario is needed in order to determine if at least some observed SNe Ia actually originate from two stars exploding.

Motivation & Objective

• To investigate whether both stars in a double degenerate binary can undergo detonation, leading to a Type Ia supernova.
• To determine if the resulting synthetic observables—light curves and spectra—can match observed SNe Ia as well as isolated double detonation models.
• To explore the impact of companion detonation on ejecta mass, elemental abundances, and nebular-phase features.
• To assess the viability of this two-star explosion scenario as a viable channel for SNe Ia, particularly in explaining observational scatter and peculiar features.
• To provide a foundation for future non-LTE radiative transfer and 3D simulations to distinguish this scenario from other SN Ia progenitor models.

Proposed method

• Conducted 2D simulations using the FLASH code to model the hydrodynamics of a carbon-oxygen white dwarf undergoing a double detonation.
• Tracked the propagation of the detonation wave through the primary star’s core and its impact on the degenerate companion.
• Simulated the subsequent detonation of the companion star, resulting in either a triple or quadruple detonation scenario.
• Performed multi-dimensional radiative transfer calculations using the Sedona code to generate synthetic light curves and spectra up to ~50 days post-explosion.
• Varied progenitor mass configurations (e.g., 0.40 M☉ He companion, 0.90 M☉ CO primary) to explore parameter space and assess observational degeneracy.
• Compared synthetic observables with observed SNe Ia, including peak brightness, decline rates, and spectral features, to evaluate model fidelity.

Figure 1: Multiband light curves from the detonation of an isolated 1.00 $M_{\odot}$ WD, compared with that of a double detonation of a thin helium shell 1.02 $M_{\odot}$ WD (Boos et al., 2021 ; Shen et al., 2021b ) . Three lines of sight from each model are shown, where the dotted, solid, and dashe

Experimental results

Research questions

• RQ1 Can a double detonation in a primary white dwarf trigger a secondary detonation in its degenerate companion in a double degenerate binary?
• RQ2 Do the synthetic light curves and spectra from such a two-star explosion scenario match observed SNe Ia as well as isolated double detonation models?
• RQ3 How do the ejecta masses and elemental yields (especially 56Ni, 56Fe, and 40Ca) differ between one-star and two-star explosion scenarios with similar observables?
• RQ4 What observable differences might emerge in the nebular phase between single and double detonation scenarios, particularly in the distribution of Fe-group elements?
• RQ5 Can this scenario explain bimodal Fe-line features in nebular spectra, such as the 5,000 km s⁻¹ peak separation seen in some SNe Ia?

Key findings

• The triple and quadruple detonation scenarios produce synthetic light curves and spectra that match observed SNe Ia as well as isolated double detonation models.
• Despite similar peak brightness and spectral morphology, the two-star explosion scenario produces significantly different ejecta masses—e.g., 0.40 M☉ for the companion in the quadruple detonation case—compared to isolated models.
• The two-star scenario results in drastically different nucleosynthetic yields: the 0.40 M☉ He companion leaves behind 0.16 M☉ of unburnt helium, and the total 56Ni and 56Fe production differs substantially from isolated double detonation models.
• The models show non-monotonic stratification of core ejecta abundances, which may lead to observable differences in the nebular phase, including bimodal Fe-line features.
• The scenario can produce a bimodal distribution of high-mass material along the line of sight, potentially explaining double-peaked Fe lines observed in some SNe Ia, such as those reported by Dong et al. (2015).
• The full post-processed yields, ejecta profiles, and synthetic spectra are publicly available on Zenodo (10.5281/zenodo.10515767) for further analysis and comparison.

Figure 2: Spectral comparison between the 1.02 $M_{\odot}$ shelled double detonation model from Boos et al. ( 2021 ) and a bare 1.00 $M_{\odot}$ C/O WD 42 o above the equatorial plane, the line of sight at which these models disagree the most. Each pair of spectra are at the labeled time relative to