Equation Icon  ∂ρ ---+ ∇ ⋅ (ρu ) = 0, (39 ) ∂t ∂u-+ (u ⋅ ∇ )u = − 1-∇p − ∇ Φ, (40 ) ∂t ρ ∇2 Φ = 4πG ρ. (41 )