Because of the increasing ratio of surface area/mass with decreasing particle size, it can be appreciated that the 'gravitrational bonds' formed by the accumulation of gravitrons and subsequent particulate matter would be very strong.

By comparison to the Earth/Moon system, so that 40 moons were enclosed within a volume equivalent to that of the Earth, it can be imagined that although the surface gravity would not be substantially different to half that of the Earth, the combined gravitrational bonds between the Moons would be much greater. This I believe is the mechanism of atomic and sub-atomic forces.