Microlensing Discovery of a Tight, Low Mass-ratio Planetary-mass Object around an Old, Field Brown Dwarf

TL;DR

This paper reports the discovery of a planetary-mass object orbiting a brown dwarf via microlensing, with a low mass ratio and close separation, indicating possible planet-like formation around brown dwarfs.

Contribution

It presents the first microlensing detection of a low mass-ratio planetary-mass object around an old, field brown dwarf, suggesting planet formation processes around substellar objects.

Findings

Discovered a 1.9 Jupiter-mass object orbiting a brown dwarf.

The system has a low mass ratio of 0.080 and a separation of ~0.87 AU.

Indicates possible planet formation in a protoplanetary disk around brown dwarfs.

Abstract

Observations of accretion disks around young brown dwarfs have led to the speculation that they may form planetary systems similar to normal stars. While there have been several detections of planetary-mass objects around brown dwarfs (2MASS 1207-3932 and 2MASS 0441-2301), these companions have relatively large mass ratios and projected separations, suggesting that they formed in a manner analogous to stellar binaries. We present the discovery of a planetary-mass object orbiting a field brown dwarf via gravitational microlensing, OGLE-2012-BLG-0358Lb. The system is a low secondary/primary mass ratio (0.080 +- 0.001), relatively tightly-separated (~0.87 AU) binary composed of a planetary-mass object with 1.9 +- 0.2 Jupiter masses orbiting a brown dwarf with a mass 0.022 M_Sun. The relatively small mass ratio and separation suggest that the companion may have formed in a protoplanetary disk around the brown dwarf host, in a manner analogous to planets.