| Astrophysics (Index) | About |
Gravitational collapse is the shrinking of an object due to the force of gravity not being fully counteracted. The term is commonly used regarding clouds collapsing to form stars, and regarding stars shrinking, in some cases collapsing into compact objects. Gravitational collapse releases energy (gravitational collapse energy, via the Kelvin-Helmholtz mechanism), which, at one time, was thought to be the source of the Sun's energy (that the Sun is powered by a lengthy, drawn-out collapse) and is still considered a significant energy source during some phases of a star's lifetime, such as pre-main-sequence stars that have yet to trigger fusion. The energy available for such released if a body (star, cloud, etc.) collapses can be determined through the virial theorem which states a specific balance between thermal/kinetic energy versus potential energy within a system in hydrostatic equilibrium. Gravitational-collapse energy can be extreme, i.e., in strong-field gravity, and produces significant energy during the formation of compact objects.
An object balancing the inward force of gravity with the outward force of internal pressure is in hydrostatic equilibrium. An object likely first reached hydrostatic equilibrium through previous gravitational collapse, and if the internal pressure for some reason is reduced (slowly through cooling, or more quickly, as through the exhaustion of fuel for the fusion that maintains the internal temperature within stars), gravitational collapse will resume.
Some globular clusters show signs that they have undergone a type of core collapse, a gravitational collapse of the center that can raise the center's stellar number density to the point that stars there are generally no more than a few thousand AU separated.