What causes a star to turn into a black hole
A star turns into a black hole when it undergoes a gravitational collapse. This collapse occurs when a massive star runs out of nuclear fuel in its core and can no longer generate enough energy to counterbalance the force of gravity pushing it inward.
The collapse process depends on the initial mass of the star. For stars that are several times more massive than our Sun (about 3-20 times), the collapse triggers a supernova explosion. The explosion blasts away the outer layers of the star, leaving behind a dense core called a neutron star. If the remaining core is more than about three times the mass of the Sun, it will continue to collapse under its own gravity, forming a black hole.
As the core collapses, its density increases to an extreme degree, and its gravitational pull becomes so strong that it creates a region in space where the escape velocity exceeds the speed of light. This region is known as the event horizon, which marks the boundary of a black hole. Once the core collapses within the event horizon, it becomes a singularity, a point of infinite density where the laws of physics as we know them break down.
Therefore, a black hole is formed when a massive star reaches a critical mass during its gravitational collapse, leading to an infinitely dense singularity enclosed within its event horizon.