Galaxy Mergers and Stellar Evolution
Summary
Galaxy mergers are fundamental events in the hierarchical assembly of structure, in which two or more gravitationally bound systems coalesce to form a single, more massive galaxy. Such interactions reshape stellar orbits, redistribute gas and dust, and trigger bursts of star formation that profoundly influence the subsequent life cycles of stellar populations. Major mergers, involving partners of comparable mass, can drive the rapid growth of central bulges and supermassive black holes, often leading to quenching of star formation and morphological transformation into early‐type systems. Minor mergers, by contrast, contribute to the gradual accretion of stars and gas (‘ex situ’ assembly) and may preserve or regrow disc structures through the accretion of fresh material. Stellar evolution within the merger remnant proceeds under conditions of enhanced turbulence, elevated pressure and altered metallicity, thereby affecting the initial mass function, stellar lifetimes and the chemical enrichment of the interstellar medium. Across cosmic time, the balance between in situ star formation in quiescent discs and ex situ accretion via mergers shapes the global stellar mass function, the Hubble sequence and the evolution of galaxy scaling relations. Observational campaigns with facilities such as the James Webb Space Telescope have revealed the morphological diversity of mergers at high redshift, while cosmological simulations and machine‐learning techniques are refining our understanding of merger rates, environmental dependence and the connection to stellar feedback processes. Together, these approaches illuminate the interplay between gravitational dynamics and stellar physics that underpins galaxy evolution worldwide.
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Galaxy Mergers and Stellar Evolution publication trend
The graph below shows the total number of articles in galaxy mergers and stellar evolution across all publications each year (not limited to Nature Index journals).
Technical terms
Galaxy merger: The coalescence of two or more galaxies under mutual gravity, classified by mass ratio into major (comparable masses) and minor (disparate masses) events.
In situ star formation: The formation of stars from gas that is already part of the main progenitor galaxy, as opposed to accreted from external sources.
Ex situ accretion: The incorporation of stars or gas formed outside the main galaxy, typically delivered during merger events.
Major merger: A merger between galaxies whose stellar masses differ by less than a factor of four, often inducing strong dynamical and starburst activity.
Minor merger: A merger in which a smaller satellite (mass ratio greater than four to one) is assimilated by a more massive host, leading to more modest morphological and star formation effects.
References
- CEERS Key Paper. III. The Diversity of Galaxy Structure and Morphology at z = 3–9 with JWST. The Astrophysical Journal Letters (2023).
- Identifying Mergers in the Legacy Surveys with Few-shot Learning. The Astrophysical Journal Supplement Series (2024).
- A chronicle of galaxy mass assembly in the EAGLE simulation. Monthly Notices of the Royal Astronomical Society (2016).
- The role of mergers in driving morphological transformation over cosmic time. Monthly Notices of the Royal Astronomical Society (2018).
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