Radial (cylindrical) acceleration due to thermal pressure gradient (top panel), centrifugal acceleration (middle panel), and gravitational acceleration (bottom panel) at distinct epochs to study the density bump formation, which is responsible for the first fragmentation. Only the radial gravitational acceleration is directed inward. In the zoom-in view of the bottom panel, it can be seen that the inward gravitational acceleration weakens around 30 AU at t≲2 kyr, so that gas accumulates into a bump.