I am carrying out a research work and I am stuck at the first page where there is an introduction to the angular momentum and its relationship in the formation of the solar system. According to that paper, stars are formed by the accretion of interstellar cloud (or nebulla) into a young star and that when central part of the cloud will collapse to the proto-star, the sorrounding cloud will rotate even more faster since angular momentum is conserved in Nebula.* Furthermore, it is also mentioned that '...it is not clear how the angular momentum in the accretion disk is transported out of the system in order to allow the dusts and gases collapse into the proto star.** My question is why is the transfer of mass in this case being looked upon as the transfer of angular momentum? As far as I know angular momentum has something to do with motion rather than the transfer of mass. Also how to visualize physically the transfer of angular momentum. I am stuck!
I think the problem is that, given conservation of angular momentum it's hard to see how stuff gets close to the centre of the system at all: as the cloud collapses its moment of inertia decreases and so its angular velocity should increase. So if you took a big cloud and collapsed the whole cloud down to a star then you'd end up with a star with an enormous rate of spin, or in fact you'd not get a star at all because it just would not collapse far enough.
So what needs to happen is that some of the material collapses to form the star, and in doing so it must transfer angular momentum to the remaining material, so the star can form. And the mechanism for transferring angular momentum seems not to be known.
In the Solar system, for instance, the Sun accounts for essentially all the known mass, but only a tiny proportion of the angular momentum of the whole system, so somehow a lot of the angular momentum got transferred to the planets (which probably really means 'to Jupiter' as to a reasonable approximation it's the only planet).
This is a very hand-wavy argument but I think you can see what I mean.