Which event triggers the start of black hole formation?
A small to medium mass star explodes as supernova
The gravitational forces acting on a massive star push it outward rapidly
A massive star depletes its stories of hydrogen and helium
Radiation emitted by a massive star increse
A small to medium mass star exploding as a supernova does not trigger the start of black hole formation. It can, however, result in the formation of a neutron star.
The gravitational forces acting on a massive star pushing it outward rapidly also do not trigger black hole formation. This scenario is often associated with the end of a star's life, but it does not lead directly to black hole formation.
A massive star depleting its stores of hydrogen and helium is also not the event that triggers black hole formation. This phase usually occurs before the actual formation of a black hole.
The correct answer is "Radiation emitted by a massive star increases." When a massive star runs out of nuclear fuel and starts burning heavier elements through nuclear fusion, it generates an enormous amount of energy in the form of radiation. This intense radiation causes the core of the star to collapse under its own gravity, leading to the formation of a black hole.