Primordial obliquities of brown dwarfs and super-Jupiters from fragmenting gravito-turbulent 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 - . Subsequent collisions between fragments can further alter the obliquity distribution, up to 90 - 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 - , and gravitationally stir leftover material to many times the pre-fragmentation disc thickness.