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.
Source: [Phys.org](https://phys.org/news/2026-06-collapsing-stars-spawn-mini-universes.html)