Galaxy interaction

Galaxy interaction is the gravitational influence galaxies exert on one another during close encounters or mergers. It can distort their shapes, alter star formation, and reshape their structure.

Tidal force: A difference in gravitational force across an extended object, which can stretch or disrupt it. Uneven gravity across each galaxy pulls stars and gas into extended tidal features.
Antennae Galaxies: A pair of colliding galaxies in Corvus whose long tidal tails give them an insect-like appearance. Their prominent tails and star-forming regions show an ongoing merger.
Starburst galaxy: A galaxy forming stars at a rate far above the long-term average for its mass. Tidal forces can drive gas inward and trigger a brief surge of star formation.
Galaxy: A gravitationally bound system of stars, gas, dust, and dark matter. Interactions act on whole galaxies and their extended matter distributions.
Major merger: A merger between galaxies of comparable mass, commonly defined by a mass ratio no more unequal than about 3:1. Comparable masses can strongly disrupt both galaxies and erase their disks.
Dynamical friction: The loss of orbital energy by a massive body moving through a background of matter. It drains orbital energy from interacting galaxies, helping bring them together.
Cartwheel Galaxy: A ring galaxy whose structure is thought to have formed after a smaller galaxy passed through its center. Its expanding ring illustrates the effects of a near-central collision.
Galaxy morphology: The classification and structural description of galaxies by features such as disks, bars, and spheroids. Mergers can transform orderly disks into more spheroidal remnants.
Dark matter halo: An extended distribution of dark matter surrounding a galaxy or galaxy group. Halo gravity influences encounter orbits and helps bind galaxies before their visible parts collide.
Minor merger: A merger in which a much less massive galaxy joins a larger one. A small companion can alter its host while leaving much of the host disk intact.

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