The entry geometry and velocity of planetary debris into the Roche sphere of a white dwarf

TL;DR

This study uses extensive simulations to analyze how asteroid entry points, angles, and velocities into a white dwarf's Roche sphere depend on planetary characteristics, impacting debris geometry and accretion.

Contribution

It provides the first comprehensive analysis of asteroid injection geometry into white dwarf Roche spheres across different planetary masses and eccentricities.

Findings

Lower planetary masses lead to more anisotropic asteroid injection.

Reduced planetary mass decreases the likelihood of head-on asteroid encounters.

Dynamical activity within the Roche sphere can reveal hidden planetary system architectures.

Abstract

Our knowledge of white dwarf planetary systems predominately arises from the region within a few Solar radii of the white dwarfs, where minor planets break up, form rings and discs, and accrete onto the star. The entry location, angle and speed into this Roche sphere has rarely been explored but crucially determines the initial geometry of the debris, accretion rates onto the photosphere, and ultimately the composition of the minor planet. Here we evolve a total of over 10^5 asteroids with single-planet N-body simulations across the giant branch and white dwarf stellar evolution phases to quantify the geometry of asteroid injection into the white dwarf Roche sphere as a function of planetary mass and eccentricity. We find that lower planetary masses increase the extent of anisotropic injection and decrease the probability of head-on (normal to the Roche sphere) encounters. Our results suggest that one can use dynamical activity within the Roche sphere to make inferences about the hidden architectures of these planetary systems.