Initial Stellar Model
In each of the three simulations, the initial stars are differentially rotating polytropes, with n = 1:
P = K ρ0Γ, Γ = 1 + 1/n
with K and Γ constant. They each have a rest mass M0 = 0.20 in units where the maximum nonrotating mass is 0.17. The rotation law is given relativistically by:
utuφ = Req2 A2 (Ωc - Ω)
where Ω is the angular velocity of the fluid, Ωc is the value of Ω on the rotation axis, and Req is the equatorial coordinate radius. A is a parameter that measures the degree of differential rotation, chosen to be 1 in the simulations. In the Newtonian limit, the rotation law is given by
Ω ≈ Ωc/(1 + ϖ2/Req2)
where ϖ is the cylindrical radius. Collapse is induced by depleting the initial pressure by a factor of 0.01.