Gravity plays a crucial role in the formation of a black hole. When a massive star exhausts its nuclear fuel, it can no longer produce the outward pressure needed to counterbalance the inward pull of gravity. As a result, gravity overwhelms all other forces, causing the star to collapse under its immense self-gravitational force. The collapse is a catastrophic event known as a supernova.
During the supernova explosion, the outer layers of the star are expelled into space, leaving behind a dense, compact core called a stellar remnant. If the core's mass is above a specific threshold known as the Tolman-Oppenheimer-Volkoff (TOV) limit, which is roughly 3 times the mass of the Sun (the exact threshold depends on various factors), the gravitational force becomes so intense that even light cannot escape from its surface. This highly dense and compact object is what we call a black hole.
The collapse of a massive star into a black hole occurs because the gravitational force becomes extremely concentrated in a small region. As matter collapses inward, it becomes denser and denser, causing space-time to curve more and more. Eventually, the curvature becomes so extreme that a region called an event horizon forms around the collapsed core. The event horizon is the boundary beyond which nothing, not even light, can escape the black hole's gravitational pull.
Inside the event horizon, the gravitational pull is so strong that it distorts space and time, creating a region of infinite density known as a singularity at the center of the black hole. Our current understanding of physics breaks down at the singularity, and we don't yet have a complete theory that describes the behavior of matter under such extreme conditions.
In summary, gravity is responsible for collapsing a massive star into a black hole by overcoming all other forces and causing the star's core to become so dense and compact that it forms an event horizon from which nothing can escape, leading to the creation of a singularity at the center.