A hot subdwarf-white dwarf super-Chandrasekhar candidate supernova Ia progenitor

TL;DR

This paper reports the discovery of a binary system with a total mass exceeding the Chandrasekhar limit, likely to merge and produce a supernova Ia, providing new insights into supernova progenitors.

Contribution

It presents the first detailed observation of a hot subdwarf-white dwarf binary exceeding the Chandrasekhar limit as a supernova Ia progenitor candidate.

Findings

Total system mass exceeds Chandrasekhar limit

System will merge in 70 million years

Constraints on hot subdwarf-white dwarf binaries as progenitors

Abstract

Supernova Ia are bright explosive events that can be used to estimate cosmological distances, allowing us to study the expansion of the Universe. They are understood to result from a thermonuclear detonation in a white dwarf that formed from the exhausted core of a star more massive than the Sun. However, the possible progenitor channels leading to an explosion are a long-standing debate, limiting the precision and accuracy of supernova Ia as distance indicators. Here we present HD265435, a binary system with an orbital period of less than a hundred minutes, consisting of a white dwarf and a hot subdwarf -- a stripped core-helium burning star. The total mass of the system is 1.65+/-0.25 solar-masses, exceeding the Chandrasekhar limit (the maximum mass of a stable white dwarf). The system will merge due to gravitational wave emission in 70 million years, likely triggering a supernova Ia event. We use this detection to place constraints on the contribution of hot subdwarf-white dwarf binaries to supernova Ia progenitors.