Extremely heavy stars collapse directly into black holes when their fuel runs out because they cannot fight their own gravity.

Stars are in a constant tug-of-war. The heat from nuclear fusion pushes outward, while gravity pulls inward. When a giant star—one that is at least 25 times heavier than our Sun—runs out of fuel, the outward push stops. Gravity wins instantly. With nothing left to hold it up, the star's core crushes down under its own massive weight, collapsing completely into a black hole in less than a second.