Discovery of the Coldest Imaged Companion of a Sun-Like Star

TL;DR

This paper reports the discovery of GJ 758 B, the coldest imaged companion around a Sun-like star, with a unique position between typical formation zones, providing insights into substellar companion formation.

Contribution

First direct imaging of a very cold, T-type substellar companion at an intermediate orbit around a Sun-like star, expanding understanding of planetary and brown dwarf formation.

Findings

GJ 758 B has a temperature of 550-640 K.

It is one of the coldest companions imaged in thermal light.

An additional candidate companion was detected.

Abstract

We present the discovery of a brown dwarf or possible planet at a projected separation of 1.9" = 29 AU around the star GJ 758, placing it between the separations at which substellar companions are expected to form by core accretion (~5 AU) or direct gravitational collapse (typically >100 AU). The object was detected by direct imaging of its thermal glow with Subaru/HiCIAO. At 10-40 times the mass of Jupiter and a temperature of 550-640 K, GJ 758 B constitutes one of the few known T-type companions, and the coldest ever to be imaged in thermal light around a Sun-like star. Its orbit is likely eccentric and of a size comparable to Pluto's orbit, possibly as a result of gravitational scattering or outward migration. A candidate second companion is detected at 1.2" at one epoch.