Self-gravitation

Self-gravity is the gravitational force exerted on a body, or a group of bodies, by the body(ies) that allows it/them to be held together. Self-gravity (self-gravitation) has important effects in the fields of astronomy, physics, seismology, geology, and oceanography. Self-gravity has important impacts in regard to the physical behavior on large scale (planet size or larger) objects, such as the oceans on Earth or the rings of Saturn. The equation to calculate the effects of self-gravitation were made exact by Lynden-Bell for the purpose of giving an exact description of models for rotating flattened globular clusters, which was a crucial step in understanding how clusters of stars interact with each other. Self-gravity deals with large-scale observations in fields outside of astronomy as well. Self-gravity does not typically appear as the central focus of scientific research, but understanding it and being able to include its effects mathematically increases the accuracy of models and understanding large-scale systems.

Self-gravity must be taken into account for astronomers because the bodies being dealt with are large enough to have gravitational effects on each other and within the bodies themselves. Self-gravity affects bodies passing each other in space within the sphere defined by the Roche limit because relatively small bodies could be torn apart by differential attraction, but typically the effects of self-gravitation keep the smaller body intact because the smaller body becomes elongated and the gravity of the body is able to overcome the momentum from this interaction between bodies. This has been demonstrated on Saturn because the rings are a function of inter-particle self-gravity. Self-gravity is also necessary to understand quasi-stellar object discs and how accretionary discs form and are stable and the role of self-gravity, as well as the importance of other factors in stabilizing these discs around quasi-stellar objects. Self-gravitational forces are very important in the formation of planetesimals, and indirectly the formation of planets, which is critical to understanding how planets and planetary systems form and develop with time. Self-gravity is very important on a range of scales, from the formation of rings around individual planets to the formation of planetary systems, and without fully understanding how to account for self-gravity, we will not be able to fully understand the system we live in on large scales.

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