Prograde spin-up during gravitational collapse

Asteroids, planets, stars in some open clusters, and molecular clouds appear to possess a preferential spin-orbit alignment, pointing shared processes that tie their rotation at birth larger parent structures. We present new mechanism describes how collections of particles, or “clouds”, gain prograde rotational component when they collapse contract while subject an external, central force. The effect is geometric origin, as relative shear on curved orbits moves center-of-mass slightly inward toward the external potential during collapse, transferring orbital angular momentum into aligned (prograde) rotation. perform illustrative analytical N -body calculations show this process spin-up proceeds quadratically time ( δL rot ∝ t 2 ) until nears completion. total increases with size cloud prior its /L H R cl /R 5 , typically distance source L r 0 ). For form interface self-gravity ~ ), means even setups large initial retrograde prograde-spinning objects. Being effect, persists around any triggers shear, those where strongly retrograde. highlight application Solar System, can explain frequency binary objects Kuiper belt