Survival of Planets Around Shrinking Stellar Binaries

TL;DR

This paper investigates how planets can survive or be affected during the orbital decay of binary stars caused by the Lidov-Kozai mechanism, predicting possible configurations of circumbinary planets around compact binaries.

Contribution

It introduces a model for the orbital evolution of planets around decaying binaries, highlighting survival and misalignment outcomes during binary orbital decay.

Findings

Planets can survive binary orbital decay and become misaligned.

Eccentricity oscillations can lead to planet ejection or consumption.

Circumbinary planets around compact binaries may still exist.

Abstract

The discovery of transiting circumbinary planets by the Kepler mission suggests that planets can form efficiently around binary stars. None of the stellar binaries currently known to host planets has a period shorter than 7 days, despite the large number of eclipsing binaries found in the Kepler target list with periods shorter than a few days. These compact binaries are believed to have evolved from wider orbits into their current configurations via the so-called Lidov-Kozai migration mechanism, in which gravitational perturbations from a distant tertiary companion induce large-amplitude eccentricity oscillations in the binary, followed by orbital decay and circularization due to tidal dissipation in the stars. Here we explore the orbital evolution of planets around binaries undergoing orbital decay by this mechanism. We show that planets may survive and become misaligned from their host binary, or may develop erratic behavior in eccentricity, resulting in their consumption by the stars or ejection from the system as the binary decays. Our results suggest that circumbinary planets around compact binaries could still exist, and we offer predictions as to what their orbital configurations should be like.