If neutron stars don't produce energy from fusion, like normal stars, how can they shine in visible light?

Although it is true that neutron stars have, for the most part, consumed all their internal thermonuclear fuel, they tap into other energy sources to produce light. Indeed, neutron stars are remarkably "resourceful" and employ a variety of physical mechanisms to make themselves visible.A newborn neutron star is incredibly hot — it is, after all, the surviving core of a star that has just collapsed and exploded as a supernova. Gravitational energy released during the star's collapse represen...