Binary orbits as the driver of gamma-ray emission and mass ejection in classical novae

TL;DR

This study uses high-resolution radio imaging to show that the shape of nova ejecta, influenced by binary star motion, drives shock formation and gamma-ray emission in classical novae.

Contribution

It demonstrates that binary interaction shapes nova ejecta and creates internal shocks, explaining gamma-ray emission in classical novae, a novel insight into their mass ejection mechanisms.

Findings

Ejecta shaped by binary motion with polar winds and equatorial material.

Synchrotron emission observed at shock interfaces indicating relativistic particles.

Binary shaping likely common, explaining widespread gamma-ray emission in novae.

Abstract

Classical novae are the most common astrophysical thermonuclear explosions, occurring on the surfaces of white dwarf stars accreting gas from companions in binary star systems. Novae typically expel ~10^(-4) solar masses of material at velocities exceeding 1,000 kilometres per second. However, the mechanism of mass ejection in novae is poorly understood, and could be dominated by the impulsive flash of thermonuclear energy, prolonged optically thick winds, or binary interaction with the nova envelope. Classical novae are now routinely detected in gigaelectronvolt gamma-ray wavelengths, suggesting that relativistic particles are accelerated by strong shocks in the ejecta. Here we report high-resolution radio imaging of the gamma-ray-emitting nova V959 Mon. We find that its ejecta were shaped by the motion of the binary system: some gas was expelled rapidly along the poles as a wind from the white dwarf, while denser material drifted out along the equatorial plane, propelled by orbital motion. At the interface between the equatorial and polar regions, we observe synchrotron emission indicative of shocks and relativistic particle acceleration, thereby pinpointing the location of gamma-ray production. Binary shaping of the nova ejecta and associated internal shocks are expected to be widespread among novae, explaining why many novae are gamma-ray emitters.