Peculiar galaxy

A galaxy with unusual structure, morphology, or activity that distinguishes it from typical galaxies. Its peculiarities may result from interactions, mergers, or unusual internal processes.

Antennae Galaxies: A pair of colliding galaxies whose long tidal tails resemble insect antennae. Their distorted shapes and active star formation make them a classic interacting example.
Galaxy merger: The process in which two or more galaxies combine through gravitational interaction. Mergers can distort a galaxy's structure and trigger bursts of star formation.
Halton Arp: An American astronomer who published a landmark atlas of peculiar galaxies in 1966. His atlas made strikingly unusual galaxies a systematic subject of observation.
Galaxy evolution: The changes in galaxies' properties and structures over cosmic time. Peculiar systems expose episodes of transformation that regular galaxies may conceal.
Mice Galaxies: A pair of interacting galaxies with long, narrow tidal tails. Their dramatic tails illustrate how gravity can produce peculiar morphology.
Tidal tail: An elongated stream of stars and gas pulled from a galaxy by gravitational forces. Tidal tails are visible signatures of strong interactions behind many peculiar forms.
Atlas of Peculiar Galaxies: A 1966 catalog by Halton Arp documenting 338 unusual galaxies and galaxy groups. It supplied many of the canonical examples associated with this label.
Tidal dwarf galaxy: A small galaxy formed from gas and stars pulled out during a larger galaxy's interaction. Some peculiar tidal structures can condense into new, self-gravitating galaxies.
Cartwheel Galaxy: A ring galaxy formed after a smaller galaxy passed through its central region. Its expanding ring and spokes give it an unusually distinctive structure.
Starburst galaxy: A galaxy forming stars at a rate far above the typical rate for its mass. Interaction-driven starbursts can make a galaxy unusually bright and active.

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Irregular galaxyRelated: The term can describe disturbed galaxies without making irregularity their formal morphological class.