When fusion stops, a stellar core is held up only by quantum degeneracy pressure or, past a mass limit, nothing at all. Which endpoint it becomes depends purely on remnant mass:
M < 1.44 M☉ → white dwarf (electron degeneracy)
1.44 ≤ M < ~3 M☉ → neutron star (neutron degeneracy)
M ≥ ~3 M☉ → black hole (total collapse)
A white dwarf's radius shrinks as it gains mass, R ∝ M^(-1/3), until the Chandrasekhar limit (1.44 M☉) is reached and electron degeneracy pressure can no longer win against gravity. A neutron star is instead held up by neutron degeneracy pressure at nuclear density, so its radius stays near 11 km almost regardless of mass — until the Tolman–Oppenheimer–Volkoff limit is crossed and even that fails. Beyond it, gravity wins completely and the surface falls inside the Schwarzschild radius:
R_s = 2GM / c²
v_esc = √(2GM / r)
Escape velocity is shown at the object's own surface (or event horizon for a black hole, where it saturates at exactly the speed of light). The grid below the object visualizes spacetime curvature — deeper and narrower as compactness (M/R) increases — and the accretion disk shows companion gas heating by friction as it spirals toward the remnant, the same mechanism that makes real neutron stars and black holes visible.