Populations of planets in multiple star systems

TL;DR

This paper reviews the abundance, formation, and characteristics of planets in multi-star systems, highlighting recent findings on their distribution, formation mechanisms, and the influence of stellar multiplicity on planet occurrence.

Contribution

It provides a comprehensive overview of observational data and theoretical insights into planets in multi-star systems, emphasizing new findings on their frequency and formation processes.

Findings

Most planets are circumstellar, with close binaries (<50 AU) having fewer planets.

Hot Jupiters are more common in wider binaries (>100 AU), but not due to Kozai-Lidov migration.

Circumbinary planets are found around main sequence and evolved binaries, with a high frequency of gas giants around main sequence binaries.

Abstract

Astronomers have discovered that both planets and binaries are abundant throughout the Galaxy. In combination, we know of over 100 planets in binary and higher-order multi-star systems, in both circumbinary and circumstellar configurations. In this chapter we review these findings and some of their implications for the formation of both stars and planets. Most of the planets found have been circumstellar, where there is seemingly a ruinous influence of the second star if sufficiently close (<50 AU). Hosts of hot Jupiters have been a particularly popular target for binary star studies, showing an enhanced rate of stellar multiplicity for moderately wide binaries (>100 AU). This was thought to be a sign of Kozai-Lidov migration, however recent studies have shown this mechanism to be too inefficient to account for the majority of hot Jupiters. A couple of dozen circumbinary planets have been proposed around both main sequence and evolved binaries. Around main sequence binaries there are preliminary indications that the frequency of gas giants is as high as those around single stars. There is however a conspicuous absence of circumbinary planets around the tightest main sequence binaries with periods of just a few days, suggesting a unique, more disruptive formation history of such close stellar pairs.