Capture into Apsidal Resonance and the Decimation of Planets around In-spiraling Binaries

TL;DR

This paper investigates how a secular resonance caused by general relativity in tightening binary star systems can lead to the destruction or ejection of circumbinary planets, explaining their observed scarcity.

Contribution

It introduces a new dynamical mechanism involving relativistic precession resonance that explains the decimation of circumbinary planets around close binaries.

Findings

Most CBPs encounter the resonance during binary tightening.

A significant fraction of CBPs are destroyed or ejected due to this resonance.

Surviving CBPs are on low-probability, distant orbits.

Abstract

Transiting circumbinary planets (CBPs) are conspicuously rare, and entirely absent around stellar binaries with periods $\leq 7$ days. Here, we exploit a secular resonance to stimulate the orbit of a CBP into strong, disruptive interactions with the host binary. The process requires no tertiary companion and is triggered when the general-relativistic precession of a tightening binary matches the Newtonian precession it induces in its companion planet. Adiabatic capture in this resonance sees the binary draining angular momentum from the CBP's orbit which grows steadily in eccentricity until destabilization, and eventual ejection or engulfment. We map this resonance in phase space, then investigate the dynamical outcomes of encounter in the course of tidally shrinking binaries. With the help of orbit averaged simulations of a suite of systems, we find that, around tightening binaries: eight out of ten CBPs encounter and are captured in the resonance; three out of four are `destroyed'; and survivors lurk on remote, low-transit-probability orbits. This suggests that the very process which forms tight binaries effectively clears the region where transiting CBPs could reside.