Detectable close-in planets around white dwarfs through late unpacking

TL;DR

This study uses long-term simulations to show how planetary systems around stars evolve into configurations with close-in planets after the star becomes a white dwarf, explaining observed phenomena and potential detectability.

Contribution

It demonstrates how stable, multi-planet systems can become dynamically unpacked and produce detectable close-in planets during white dwarf cooling, a novel insight into post-main-sequence planetary evolution.

Findings

Unpacked planetary systems can produce temporary close-in planets.

Simulations span the age of the Universe for various stellar masses.

Provides a mechanism for planetary system dynamical evolution after stellar death.

Abstract

Although 25%-50% of white dwarfs (WDs) display evidence for remnant planetary systems, their orbital architectures and overall sizes remain unknown. Vibrant close-in (~1 Solar radius) circumstellar activity is detected at WDs spanning many Gyrs in age, suggestive of planets further away. Here we demonstrate how systems with 4 and 10 closely-packed planets that remain stable and ordered on the main sequence can become unpacked when the star evolves into a WD and experience pervasive inward planetary incursions throughout WD cooling. Our full-lifetime simulations run for the age of the Universe and adopt main sequence stellar masses of 1.5, 2.0 and 2.5 Solar masses, which correspond to the mass range occupied by the progenitors of typical present-day WDs. These results provide (i) a natural way to generate an ever-changing dynamical architecture in post-main-sequence planetary systems, (ii) an avenue for planets to achieve temporary close-in orbits that are potentially detectable by transit photometry, and (iii) a dynamical explanation for how residual asteroids might pollute particularly old WDs.