The Fate of Exoplanets and the Red Giant Rapid Rotator Connection

TL;DR

This study models the orbital decay of exoplanets around evolving stars, suggesting many are ingested during the red giant phase and potentially explain some rapid rotators, with implications for exoplanet demographics.

Contribution

It introduces a combined stellar evolution and tidal friction model to predict exoplanet ingestion and explores its connection to red giant rapid rotators, a novel approach in the field.

Findings

Most planets within 2 AU are expected to be ingested during red giant evolution.

Planet accretion may explain some red giant rapid rotators.

Not all rapid rotators can be accounted for by planetary ingestion.

Abstract

We have computed the fate of exoplanet companions around main sequence stars to explore the frequency of planet ingestion by their host stars during the red giant branch evolution. Using published properties of exoplanetary systems combined with stellar evolution models and Zahn's theory of tidal friction, we modeled the tidal decay of the planets' orbits as their host stars evolve. Most planets currently orbiting within 2 AU of their star are expected to be ingested by the end of their stars' red giant branch ascent. Our models confirm that many transiting planets are sufficiently close to their parent star that they will be accreted during the main sequence lifetime of the star. We also find that planet accretion may play an important role in explaining the mysterious red giant rapid rotators, although appropriate planetary systems do not seem to be plentiful enough to account for all such rapid rotators. We compare our modeled rapid rotators and surviving planetary systems to their real-life counterparts and discuss the implications of this work to the broader field of exoplanets.