A Spectroscopic Quadruple As a Possible Progenitor of Sub-Chandrasekhar Type Ia Supernovae

Binaries have received much attention as possible progenitors of type Ia supernova explosions1, but long-term gravitational effects2,3 in tight triple or quadruple systems could also play a key role in producing type Ia supernovae. Here we report on the properties of a spectroscopic quadruple found within a star cluster: the 2 + 2 hierarchical system HD 744384. Its membership in the open cluster IC 2391 makes it the youngest (43 Myr) spectroscopic quadruple known to us, and among the quadruple systems with the shortest outer orbital period. The eccentricity of the 6 yr outer period is 0.46, and the two inner orbits, with periods of 20.6 d and 4.4 d and eccentricities of 0.36 and 0.15, are not coplanar. Using an innovative combination of ground-based high-resolution spectroscopy5–7 and Gaia/Hipparcos astrometry8–11, we show that this system is undergoing secular interaction, which probably pumped the eccentricity of one of the inner orbits higher than expected for the spectral types of its components. We compute the future evolution of HD 74438 and show that this system is an excellent candidate progenitor of sub-Chandrasekhar type Ia supernovae through white dwarf mergers. Taking into account the contribution of this specific type of type Ia supernova accounts for the chemical evolution of iron-peak elements in the Galaxy better than considering only near Chandrasekhar-mass type Ia supernovae12. Spectroscopic and astrometric characterization of a quadruple star system composed of a pair of binary stars shows that the components will eventually merge to form white dwarfs, before potentially generating a sub-Chandrasekhar type Ia supernova.