Perhaps there is no brown dwarf desert? A study of sub-stellar companions with Gaia DR3

TL;DR

This study uses Gaia DR3 data and Bayesian analysis to investigate the brown dwarf desert, suggesting a higher occurrence rate of brown dwarf companions in close orbits around Sun-like stars than previously thought, with implications for future Gaia data releases.

Contribution

It provides the first large-scale Bayesian analysis of Gaia DR3 data to estimate brown dwarf companion occurrence rates in the brown dwarf desert period range.

Findings

Approximately 10.4% of nearby Sun-like stars may have brown dwarf companions within 5 years.

High-mass brown dwarfs (>50MJ) are relatively rare in this period range.

Predictions for future Gaia DR4 data suggest more discoveries of brown dwarf companions.

Abstract

The brown dwarf desert describes a range of orbital periods (<5 years) in which fewer brown dwarf-mass companions have been observed around Sun-like stars, when compared to planets and low mass stellar companions. It is therefore theorised that brown dwarf companions are unlikely to form or remain in this period range. The Gaia space telescope is uniquely sensitive to companions in this period range, making it an ideal tool to conduct a survey of the brown dwarf desert. In this study, we use Bayesian inference to analyse data from nearby (<200pc) Sun-like stars in Gaia's DR3 catalogue, assuming single companions. From this, we identify 2673 systems (2.41% of the sample) with possible brown dwarf companions in this period range. Accounting for observational biases, we find that 10.4+0.8-0.6% of nearby Sun-like stars have astrometric errors consistent with a brown dwarf-mass companion with a period less than 5 years, significantly higher than previous studies which reported occurrence rates of <1%. However, we acknowledge the limitations of DR3 and are unable to make a definitive statement without epoch data. By simulating epoch data with multiple companions, we find that, while some of the data can be explained by multiple low-mass brown dwarf companions and high-mass planets (>10MJ), high-mass brown dwarfs (>50MJ) in this period range are comparatively rare. Finally, we used our studies of the brown dwarf distribution to predict the number of companions in the brown dwarf desert we can expect to discover in DR4.