An ultra-massive fast-spinning white dwarf in a peculiar binary system

TL;DR

This paper reports the discovery of an ultra-massive, fast-spinning white dwarf in a binary system, which could potentially reach the Chandrasekhar limit and explode as a Type Ia supernova.

Contribution

It provides dynamical measurements confirming the existence of an ultra-massive white dwarf in a binary, highlighting its potential to become a supernova.

Findings

White dwarf mass > 1.2 Msun confirmed by dynamical measurements

The system is a post-common envelope binary with a hot subdwarf

Potential to reach Chandrasekhar limit and explode as a Type Ia supernova

Abstract

White dwarfs typically have masses in a narrow range centered at about 0.6 solar masses (Msun). Only a few ultra-massive white dwarfs (M>1.2 Msun) are known. Those in binary systems are of particular interest because a small amount of accreted mass could drive them above the Chandrasekhar limit, beyond which they become gravitationally unstable. Using data from the XMM-Newton satellite, we show that the X-ray pulsator RX J0648.0-4418 is a white dwarf with mass > 1.2 Msun, based only on dynamical measurements. This ultra-massive white dwarf in a post-common envelope binary with a hot subdwarf can reach the Chandrasekhar limit, and possibly explode as a Type Ia supernova, when its helium-rich companion will transfer mass at an increased rate through Roche lobe overflow.