Galaxy merger

A galaxy merger is an event in which two or more galaxies interact gravitationally and combine into a single galaxy. It can reshape their stars, gas, and central black holes without requiring many stars to collide directly.

Dynamical friction: A drag-like effect in which a moving massive object loses momentum through gravitational interactions with surrounding matter. It drains orbital energy from merging galaxies and helps bring them together.
Antennae Galaxies: A pair of interacting galaxies in Corvus, joined by long tidal tails and undergoing vigorous star formation. Their overlapping disks and tails show a nearby merger in progress.
Elliptical galaxy: A galaxy with a smooth, rounded appearance and little organized disk structure. Repeated mergers can scramble stellar orbits and help build massive elliptical galaxies.
Hierarchical structure formation: A cosmological model in which small structures form first and combine into progressively larger ones. It places galaxy mergers within the broader assembly of cosmic structure.
Galaxy merger rate: The frequency of galaxy mergers as a function of cosmic time and galaxy properties. Its measured value tests models of how rapidly galaxies assemble.
Tidal interaction: A gravitational disturbance caused by differences in force across an extended object. Uneven gravity pulls stars and gas into tails, bridges, and distorted shapes.
Mice Galaxies: A pair of interacting galaxies in Coma Berenices, each drawn into a long tidal tail. Their pronounced tails illustrate how gravity rearranges stars during close encounters.
Galactic bulge: A dense central concentration of stars within a galaxy, often surrounding its central black hole. Redistributed stars and inflowing gas can enlarge a galaxy’s central bulge.
Dark matter halo: An extended, gravitationally dominant distribution of dark matter surrounding a galaxy or galaxy group. Merging halos bring galaxies together and influence their orbits before the visible systems combine.
Merger tree: A branching record of how a galaxy’s progenitors combine through cosmic history. Reconstructing merger histories links present-day galaxies to their earlier components.

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