A universal brown dwarf desert formed between planets and stars

TL;DR

This study analyzes a large sample of giant planets and brown dwarfs to identify a distinct brown dwarf desert around 30 Jupiter masses, supporting the idea of dual formation mechanisms for these objects.

Contribution

It provides the first rigorous statistical analysis of a large, unified sample, confirming the brown dwarf desert and proposing dual formation scenarios supported by population synthesis models.

Findings

Identification of a brown dwarf desert at ~30 M_J

Discovery of a new population of giant planets beyond the water-ice line

Evidence for two different formation pathways based on metallicity and eccentricity trends

Abstract

Giant planets and brown dwarfs play a crucial role in star and planet formation, as they are situated at the boundary between planets and stars with uncertain formation mechanisms. Previous observational searches for the formation boundary were hampered by the lack of large unified samples of wide-orbit giant planets and substellar companions. A combined analysis of radial velocity and astrometry mitigates this problem and has significantly enlarged the sample. Here we present a rigorous statistical analysis of the sample of 55 giant planets, brown dwarfs and low-mass stellar companions orbiting FGK stars. We quantitatively analyze the occurrence rates of brown dwarfs and identify a distinct brown dwarf desert at approximately $30\,M_\mathrm{J}$, with no evidence of disappearance up to 20 au. Unlike previous studies that predicted a declining planet occurrence rate beyond the water-ice line, we identify a new population of giant planets and low-mass brown dwarfs in this region. The metallicity and eccentricity trends in our sample suggest that these are the consequences of two different formation scenarios. Our combined population synthesis model successfully accounts for the observed brown dwarf desert, supporting the dual formation hypothesis.