Mechanism for generation of angular momentum in an astrophysical system

Why astrophysical entities rotate and so have angular momentum has long been a mystery. As a resolution to this mystery we present a mechanism for the spontaneous generation of angular momentum in astrophysical contexts. This mechanism depends on the combined presence of gravitational and magnetic fields and generates angular momentum via collisions between small numbers of charged particles and numerous, free-falling neutral particles. The mechanism is demonstrated by a 2D simulation of an N-body weakly-ionized system where ions and electrons, because of their different masses, develop different mean radial velocities upon colliding with free-falling neutrals. This velocity difference causes ions and electrons to decrease their canonical angular momentum P_θ = mv_θ +qψ/2π while at the same time the neutrals gain ordinary angular momentum L = mv_θ. The net result is that the total system canonical angular momentum is conserved as predicted by Lagrangian mechanics for an axisymmetric system. This shows that an initially non-rotating cloud of neutral particles will spontaneously start rotating when infalling neutral particles collide with a very small number of charged particles. Quantitative scaling predicts an angular momentum generation rate sufficient to convert neutral infall motion into neutral Keplerian rotation in the outer region of a protoplanetary accretion disk.