Stars shine because atoms fuse in their interiors, releasing energy. When a very massive star has exhausted its nuclear fuel, radiation pressure can no longer provide sufficient counterforce to gravity. The star then collapses under its own mass until only a single point remains: the singularity.
While the formation of a black hole appears plausible, black holes themselves continue to pose major challenges for science. How can 10 billion solar masses concentrate at a single tiny point? How can spacetime be curved infinitely at that point, the singularity? At this stage, the laws of physics break down, making it impossible to predict what happens. Moreover, black holes conceal all information from observation: Everything, including light, disappears irretrievably beyond the event horizon.