A systematic study of carbon–oxygen white dwarf mergers: Mass combinations for type Ia supernovae

Mergers of two carbon–oxygen (CO) white dwarfs (WDs) have been considered to be progenitors of Type Ia supernovae (SNe Ia). Based on smoothed particle hydrodynamics (SPH) simulations, previous studies have claimed that mergers of CO WDs lead to SN Ia explosions either in the dynamical merger phase or the stationary rotating merger remnant phase. However, the mass range of CO WDs that lead to SNe Ia has not yet been clearly identified. In the present work, we perform systematic SPH merger simulations for the WD masses ranging from $0.5M_{\odot }$ to $1.1M_{\odot }$ 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 SNe Ia explosions and estimate the mass range of CO WDs that lead to SNe Ia. We found that when both WDs are massive, i.e., in the mass range of $0.9M_{\odot }⩽M_{1,2}⩽1.1M_{\odot }$, 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 $0.7M_{\odot }⩽M_1⩽0.9M_{\odot }$ and the total mass exceeds $1.38M_{\odot }$, 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 $\lesssim 9\%$. Thus, it might be difficult to explain all galactic SNe Ia with CO WD mergers.