Which event triggers the start of a black hole formation

Answer 1

The most common trigger for the formation of a black hole is the gravitational collapse of a massive star at the end of its lifecycle. When a very massive star (about 20 times or more the mass of our Sun) runs out of fuel, it can no longer sustain the inward pressure due to nuclear fusion in its core, and gravity takes over, causing the star to collapse under its own weight. As the star collapses, its outer layers are ejected in a supernova explosion, while its core continues to collapse further under the influence of gravity, ultimately forming a black hole.