Stars originate as large bodies of slowly rotating gas. because of gravity, these clumps of gas slowly decrease in size. the angular velocity of a star increases as it shrinks because of

Stars originate as large bodies of slowly rotating gas. because of gravity, these clumps of gas slowly decrease in size. the angular velocity of a star increases as it shrinks because of the angular momentum conservation.

This is because in a rotary system with decreasing diameter, the angular momentum should be conserved (as long as the net torque is zero) based on physics conservation laws