Gravitational collapse

Core collapse scenario

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NGC 6745

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Gravitational collapse is a phenomenon of astrophysical scale where an astronomical object collapses under its own gravity. This process is fundamental in the formation of stars, black holes, and galaxies, marking a critical event in the life cycle of many celestial bodies. Gravitational collapse occurs when an object's internal pressure is insufficient to resist the object's own gravity, leading to a catastrophic collapse.

Overview

The concept of gravitational collapse is rooted in Newton's law of universal gravitation and general relativity. It plays a pivotal role in stellar evolution, where it can lead to various outcomes depending on the mass and composition of the collapsing object. For instance, the gravitational collapse of a massive interstellar cloud can initiate star formation, while for a sufficiently massive star, it can result in a supernova explosion, leaving behind a neutron star or a black hole.

Mechanism

The mechanism of gravitational collapse begins when the internal pressure (caused by thermal energy, nuclear reactions, or degeneracy pressure) of an astronomical object can no longer support its own weight against gravitational forces. This imbalance may be triggered by external factors such as the loss of energy through radiation, or internal processes like the exhaustion of nuclear fuel in a star's core.

Stages of Collapse

1. Initial Instability: The object becomes unstable to small perturbations due to an imbalance between gravitational forces and internal pressure.
2. Free-fall Collapse: The object's parts start moving inward under gravity, with the collapse rate possibly differing across its structure.
3. Core Collapse: In stars, the core collapses first, leading to high temperatures and pressures that can ignite further nuclear reactions or form a compact object.
4. Final State: The outcome of the collapse depends on the mass and composition of the collapsing object, ranging from a new star to a black hole.

Critical Mass and the Jeans Instability

The Jeans Instability criterion determines the conditions under which a cloud of gas will begin to collapse under its own gravity. This is characterized by the Jeans mass, above which gravitational forces overcome internal pressures, leading to collapse. The concept is crucial in understanding the formation of stars and other astronomical structures from interstellar gas clouds.

Outcomes

1. 1. 1. Stars

The gravitational collapse of gas clouds is the precursor to star formation. The process compresses the material, increasing its temperature until nuclear fusion reactions begin, marking the birth of a new star.

1. 1. 1. Neutron Stars and Black Holes

For stars with masses several times that of the Sun, gravitational collapse can continue beyond the formation of a white dwarf, leading to the creation of either a neutron star or a black hole, depending on the initial mass of the star.

1. 1. 1. Galaxies and Larger Structures

Gravitational collapse also plays a role in the formation of galaxies and larger structures in the universe. The collapse of vast clouds of gas and dark matter in the early universe led to the formation of galaxies, within which stars and planetary systems formed.

See Also

• Stellar nucleosynthesis
• Chandrasekhar limit
• Tolman–Oppenheimer–Volkoff limit
• Fermi gas
• Hydrostatic equilibrium