[Paper Review] Models and inlists for "Thermonuclear explosion criteria for direct and indirect collisions of CO white dwarfs: a study of the impact-parameter threshold for detonation"

Hila Glanz, Hagai B. Perets+1 more|arXiv (Cornell University)|Sep 6, 2023

Gamma-ray bursts and supernovae5 citations

TL;DR

This study uses high-resolution 3D hydrodynamic simulations with the AREPO code to determine the critical impact parameter threshold for detonation in collisions of carbon-oxygen white dwarfs. It finds that only collisions with sufficiently small impact parameters—dependent on density profile, composition, and velocity—lead to full detonation and significant 56Ni production, challenging prior assumptions that all physical collisions produce Type Ia supernovae.

ABSTRACT

The models used to produce Fig. 4 in the manuscript, and the inlist from that were used from make_co_wd package in the test-suit. Primary model of 0.8 COWD is added, and was originally created by Dr. Yossef Zenati for Pakmor et al. 2021.

Motivation & Objective

• To determine the critical impact parameter beyond which direct collisions of CO white dwarfs fail to produce detonation and Type Ia supernovae.
• To investigate how collision velocity, density profile, and composition influence the onset of detonation and 56Ni production.
• To assess the sensitivity of 56Ni yields to numerical resolution and burning limiters in 3D simulations.
• To provide an analytic criterion for the detonation threshold that aligns with numerical results, improving supernova rate estimates.
• To quantify the differences in ejecta structure, light curves, and nucleosynthesis between direct and indirect collisions.

Proposed method

• Performs 3D hydrodynamic simulations using the AREPO adaptive mesh-free Voronoi-type Eulerian code with high spatial resolution.
• Models equal-mass CO white dwarf collisions at varying impact parameters and relative velocities (from terminal to hyper-velocity regimes).
• Applies the Rankine-Hugoniot relations to derive an analytic estimate for the critical density and corresponding impact parameter threshold.
• Uses multiple burning limiters (Kushnir, default, and no limiter) to assess numerical sensitivity of 56Ni yields.
• Compares simulation results with analytic predictions to validate the detonation threshold criterion.
• Analyzes ejecta structure, element production (especially 56Ni), and shock dynamics to identify explosion conditions.

Experimental results

Research questions

• RQ1 What is the critical impact parameter beyond which a collision between two CO white dwarfs fails to produce a detonation?
• RQ2 How does the initial relative velocity of the colliding white dwarfs affect 56Ni production and the likelihood of explosion?
• RQ3 To what extent do numerical resolution and burning limiter choices influence the simulated 56Ni yields in white dwarf collision models?
• RQ4 How do indirect collisions (non-zero impact parameter) differ in nucleosynthesis and ejecta morphology from head-on collisions?
• RQ5 Can an analytic criterion based on shock compression and critical density accurately predict the detonation threshold observed in 3D simulations?

Key findings

• A critical impact parameter threshold exists beyond which collisions fail to produce detonation, even at high velocities, due to insufficient compression and heating.
• The 56Ni yield is highly sensitive to both collision velocity and numerical resolution, with high-velocity head-on collisions producing up to 0.34 M⊙ of 56Ni, while low-velocity runs produce only 0.185 M⊙.
• Simulations with lower resolution and different burning limiters show a factor of 5 variation in 56Ni production, highlighting strong numerical dependence.
• The analytic detonation threshold based on Rankine-Hugoniot relations agrees well with numerical results, enabling improved supernova rate estimates.
• Indirect collisions produce asymmetric ejecta and lower 56Ni yields than head-on collisions, with some cases showing only minor perturbations and no explosion.
• The study suggests that previous estimates of Type Ia SN rates from white dwarf collisions are overestimated by a factor of 2–3, as not all physical collisions lead to detonation.