Gravitational Collapse is the destruction of a planet or a star due to the massive power of its own gravity. In any stable object, this gravitational force is counterbalanced by the internal pressure of the object. If the inwards pointing gravitational force, however, is stronger than all outward pointing forces, this equilibrium is disturbed and a collapse occurs until the internal pressure might rise sufficiently to counterbalance again the gravity.
Gravitational collapse is at the heart of structure formation in the universe. An initial smooth distribution of matter will eventually collapse and cause the hierarchy of structures, such as clusters of galaxies, stellar groups, stars and planets. For example, a star is born through the gradual gravitational collapse of a cloud of interstellar matter. The compression caused by the collapse raises the temperature until nuclear fuel ignites in the center of the star and the collapse comes to a halt. The thermal pressure gradient (leading to expansion) compensates the gravity (leading to compression) and a star is in dynamical equilibrium between these two forces.
Gravitational collapse of a star occurs at the end of its lifetime, also called the death of the star. When all stellar energy sources are exhausted, the star will go through a gravitational collapse.This means that a star is in a "temporary" equilibrium state between a gravitational collapse at stellar birth and a further gravitational collapse at stellar death. The end states are called compact stars.
The types of compact stars are:
- White dwarfs, in which gravity is opposed by electron degeneracy pressure;
- Neutron stars, in which gravity is opposed by neutron degeneracy pressure and short-range repulsive neutron-neutron interactions mediated by the strong force;
- Black holes, in which the physics at the center is unknown.