Primordial Obliquities of Brown Dwarfs and Super-Jupiters from Fragmenting Gravito-Turbulent Discs

TL;DR

This paper uses numerical simulations to show that objects forming in gravito-turbulent discs can have a wide range of spin orientations, explaining observed obliquities of super-Jupiters and brown dwarfs.

Contribution

It demonstrates that gravito-turbulent disc fragmentation naturally produces objects with large and varied obliquities, a novel insight into their formation processes.

Findings

Obliquities up to 45° in newly formed fragments.

Collisions can alter obliquities up to 90°.

Fragments can have inclined orbits up to 20° relative to discs.

Abstract

Super-Jupiters, brown dwarfs, and stars can form from the collapse of self-gravitating discs. Such discs are turbulent, with flocculent spiral arms accelerating gas to transonic speeds horizontally and vertically. Objects that fragment from gravito-turbulent discs should spin with a wide range of directions, reflecting the random orientations of their parent eddies. We show by direct numerical simulation that obliquities of newly collapsed fragments can range up to 45$^\circ$. Subsequent collisions between fragments can further alter the obliquity distribution, up to 90$^\circ$ or down to near-zero. The large obliquities of newly discovered super-Jupiters on wide orbits around young stars may be gravito-turbulent in origin. Obliquely spinning fragments are born on orbits that may be inclined relative to their parent discs by up to 20$^\circ$, and gravitationally stir leftover material to many times the pre-fragmentation disc thickness.