Dynamical friction

Dynamical friction is the drag-like loss of orbital energy and momentum experienced by a massive body moving through a background of particles. It arises from the gravitational wake that the body induces in that background.

Gravitational wake: An overdense region of matter formed behind a gravitating object moving through a medium. The wake pulled behind a massive body exerts the gravitational force responsible for its deceleration.
Orbital decay: The gradual shrinking of an orbit as a body's orbital energy or angular momentum is removed. Dynamical friction is one mechanism that drives orbital decay in stellar and galactic systems.
Subrahmanyan Chandrasekhar: An Indian-American astrophysicist whose work established major results in stellar dynamics and compact-star theory. His 1943 analysis derived the standard estimate for drag from a distribution of field stars.
Mass segregation: The tendency for more massive stars in a cluster to become more centrally concentrated than lighter stars. Dynamical friction transfers energy from massive stars to lighter ones, promoting inward migration.
Chandrasekhar dynamical friction formula: A formula estimating gravitational drag on a massive object moving through a homogeneous background of collisionless particles. It quantifies how drag depends on the object's mass, speed, and the background's density and velocity distribution.
Galaxy merger: The gravitationally driven collision and eventual coalescence of two galaxies. Friction acting on satellite galaxies and their components helps remove orbital energy during a merger.
Stellar dynamics: The study of the motions and gravitational interactions of stars in stellar systems. Dynamical friction became a central tool for predicting long-term changes in stellar systems.
Core stalling: The slowing or cessation of a satellite's inward orbital decay near the center of a constant-density core. It marks a regime where standard dynamical-friction predictions can fail or weaken sharply.
Coulomb logarithm: A logarithmic factor describing the range of encounter scales contributing to cumulative long-range interactions. In Chandrasekhar's formula, it summarizes contributions from gravitational encounters at different impact parameters.
Globular cluster: A dense, gravitationally bound group of old stars orbiting a galaxy. Dynamical friction can make massive clusters lose orbital energy and sink toward galactic centers.

Linked from 45 pages