The Final Collapse

Stars above roughly 25 solar masses face a different fate than neutron stars. When the core collapses after a supernova, the remaining mass exceeds the Tolman-Oppenheimer-Volkoff limit of about 2 to 3 solar masses. No known force can halt the collapse.

The formation happens fast. Once the core crosses the mass threshold, collapse to a black hole takes less than a second. The event is often hidden inside the supernova explosion itself. Black holes are not cosmic vacuum cleaners.