Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of gravity. Gravitational collapse is a fundamental mechanism for structure formation in the universe. Over time an initial, relatively smooth distribution of matter, after sufficient accretion, may collapse to form pockets of higher density, such as stars or black holes.

Star formation involves a gradual gravitational collapse of interstellar medium into clumps of molecular clouds and potential protostars. The compression caused by the collapse raises the temperature until thermonuclear fusion occurs at the center of the star, at which point the collapse gradually comes to a halt as the outward thermal pressure balances the gravitational forces. The star then exists in a state of thermodynamic equilibrium. During the star's evolution a star might collapse again and reach several new states of equilibrium.

An interstellar cloud of gas will remain in hydrostatic equilibrium as long as the kinetic energy of the gas pressure is in balance with the potential energy of the internal gravitational force. Mathematically this is expressed using the virial theorem, which states that to maintain equilibrium, the gravitational potential energy must equal twice the internal thermal energy. If a pocket of gas is massive enough that the gas pressure is insufficient to support it, the cloud will undergo gravitational collapse. The critical mass above which a cloud will undergo such collapse is called the Jeans mass. This mass depends on the temperature and density of the cloud but is typically thousands to tens of thousands of solar masses.

At what is called the star's death (when a star has consumed its supply of fuel), it will undergo a contraction that can be halted only if it reaches a new state of equilibrium. Depending on the mass during its lifetime, these stellar remnants can take one of three forms:

Theoretically, there are compact exotic stars made from forms of exotic matter such as quarks or preons, but these objects remain hypothetical.

For isolated stars that formed with one to seven times the mass of the Sun, the final stage in their evolution is a white dwarf. The collapse of the stellar core to a white dwarf takes place over tens of thousands of years, while the star blows off its outer envelope to form a planetary nebula. A white dwarf can have a magnetic field, which may be a fossil remnant of its original stellar magnetic field. As gravitational contraction and the remaining nuclear burning contribute only a negligible amount to the energy output of a white dwarf, nearly all of the radiated luminosity comes from stored thermal energy. Thus, over time scales of billions of years, the temperature of the white dwarf will continue to decrease.

If it has a close orbiting companion star, a white dwarf-sized object can accrete matter from the companion, increasing the mass and potentially spinning it up. When sufficient hydrogen has been accumulated along the outer shell, it can detonate to form a nova. Since the white dwarf is not disrupted by the explosion, this cycle can occur repeatedly. Despite the thermonuclear explosion, some of the accumulated matter can be retained, allowing the white dwarf to continue to grow in mass.

The upper mass limit on the growth of a white dwarf is called the Chandrasekhar limit. This is about one and a half times the mass of the Sun, at which point gravitational collapse would start again. Before reaching this limit, the increasing density and temperature within a carbon-oxygen white dwarf initiates a new round of nuclear fusion, which is not regulated because the star's weight is supported by degeneracy rather than thermal pressure, allowing the temperature to rise exponentially. The resulting runaway carbon detonation completely blows the star apart in a Type Ia supernova.