A systematic study of carbon-oxygen white dwarf mergers: mass combinations for Type Ia supernovae

TL;DR

This study systematically investigates carbon-oxygen white dwarf mergers through high-resolution simulations to identify the mass ranges leading to Type Ia supernovae, revealing that only a small fraction of such mergers can produce SNe Ia.

Contribution

It provides a detailed, systematic analysis of WD mass combinations for SN Ia progenitors, clarifying the conditions under which mergers lead to explosions.

Findings

Massive WD mergers (0.9-1.1 M_sun) can explode during merger.

Less massive WD mergers require total mass >1.38 M_sun for explosion.

Estimated contribution of WD mergers to galactic SN Ia rate is less than 9%.

Abstract

Mergers of two carbon-oxygen (CO) white dwarfs (WDs) have been considered as progenitors of Type Ia supernovae (SNe Ia). Based on smoothed particle hydrodynamics (SPH) simulations, previous studies claimed that mergers of CO WDs lead to an SN Ia explosion either in the dynamical merger phase or stationary rotating merger remnant phase. However, the mass range of CO WDs that lead to an SN Ia has not been clearly identified yet. In the present work, we perform systematic SPH merger simulations for the WD masses ranging from $0.5~M_{\odot}$ to $1.1~M_{\odot}$ with higher resolutions than the previous systematic surveys and examine whether or not carbon burning occurs dynamically or quiescently in each phase. We further study the possibility of SN Ia explosion and estimate the mass range of CO WDs that lead to an SN Ia. We found that when the both WDs are massive, i.e., in the mass range of $0.9~M_{\odot} {\le} M_{1,2} {\le} 1.1~M_{\odot}$, they can explode as an SN Ia in the merger phase. On the other hand, when the more massive WD is in the range of $0.7~M_{\odot} {\le} M_{1} {\le} 0.9~M_{\odot}$ and the total mass exceeds $1.38~M_{\odot}$, they can finally explode in the stationary rotating merger remnant phase. We estimate the contribution of CO WD mergers to the entire SN Ia rate in our galaxy to be of ${\lt} 9\%$. So, it might be difficult to explain all galactic SNe Ia by CO WD mergers.