Giant Planets, Tiny Stars: Producing Short-Period Planets around White Dwarfs with the Eccentric Kozai-Lidov Mechanism

TL;DR

This paper proposes that the Eccentric Kozai-Lidov mechanism, combined with stellar evolution and tides, explains how giant planets can migrate to close orbits around white dwarfs, supported by observed systems.

Contribution

It demonstrates that the EKL mechanism can account for the formation of short-period planets around white dwarfs, aligning with recent observational discoveries.

Findings

EKL mechanism can produce observed planetary orbits around white dwarfs.

Constraints on potential stellar companions for WD J0914 and WD 1856.

Initial orbital parameters for the systems are determined.

Abstract

The recent discoveries of WD J091405.30+191412.25 (WD J0914 hereafter), a white dwarf likely accreting material from an ice giant planet, and WD 1856+534 b (WD 1856 b hereafter), a Jupiter-sized planet transiting a white dwarf, are the first direct evidence of giant planets orbiting white dwarfs. However, for both systems the observations indicate that the planets' current orbital distances would have put them inside the stellar envelope during the red giant phase, implying that the planets must have migrated to their current orbits after their host stars became white dwarfs. Furthermore, WD J0914 is a very hot white dwarf with a short cooling time that indicates a fast migration mechanism. Here, we demonstrate that the Eccentric Kozai-Lidov (EKL) Mechanism, combined with stellar evolution and tidal effects, can naturally produce the observed orbital configurations, assuming that the white dwarfs have distant stellar companions. Indeed, WD 1856 is part of a stellar triple system, being a distant companion to a stellar binary. We provide constraints for the orbital and physical characteristics for the potential stellar companion of WD J0914 and determine the initial orbital parameters of the WD 1856 system.