Spherical gravitational collapse: Tangential pressure and related equations of state

We derive an equation for the acceleration of a fluid element in the spheri cal gravitational collapse of a bounded compact object made up of an imperf ect fluid. We show that non-singular as well as singular solutions arise in the collapse of a fluid initially at rest and having only a tangential pre ssure. We obtain an exact solution of the Einstein equations, in the form o f an infinite series, for collapse under tangential pressure with a linear equation of state. We show that if a singularity forms in the tangential pr essure model, the conditions for the singularity to be naked are exactly th e same as in the model of dust collapse.