Recently published the study: “Searching for chemical signatures of brown dwarf formation” of J. Maldonado (INAF-OAPA)

There is a type of stars connecting giant planets and stars: the brown dwarfs. These “failed stars” have a mass ranging from 13 to 80 Jupiter masses, enough to ignite deuterium burning, but not hydrogen such as main sequence stars.

 

 

It is still not clear whether brown dwarfs form like planets or like stars. Planets form in protoplanetary disks around young stars. In particular, two formation mechanisms have been proposed for giant planets: gas accretion onto a massive rocky core (core-accretion) or after gravitational fragmentation of the discs (disc instability). Stars form instead after the gravitational collapse of gaseous clouds.

 

The study “Searching for chemical signatures of brown dwarf formation” of J. Maldonado (Astronomical Observatory of Palermo) and E. Villaver (Universidad Autónoma de Madrid), recently published on Astronomy & Astrophysics, shed some light on the formation process of brown dwarfs. The authors have analyzed high-resolution spectra of 53 FGK stars known to host a brown dwarf companion, with the aim of determine their chemical abundances and look for differences between those hosting a brown dwarf companion more and less massive  than 42.5 Jupiter masses.

 

The main result of the paper is the evidence that stars with massive brown dwarf companion share similar chemical abundances of stars without known planetary companion, while stars with low mass brown dwarf companion have slightly larger abundance of heavy elements, similarly to stars with planets. This suggests that massive brown dwarfs form like stars, just not massive enough to start burning hydrogen, while low mass brown dwarfs likely form from protoplanetary disks such as planets do.

 

The figure (link) compares the size of low-mass stars, brown dwarfs, and planets