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What evidence suggests that the Andromeda Galaxy has merged with smaller galaxies?
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Cosmology
Learn about defining and measuring the observable universe within the “whole” universe.
Evidence suggests that the Andromeda Galaxy (M31) has a history of colliding with and accreting smaller galaxies through several observable features:
- Companion Galaxy M32: This close companion exhibits a structure indicating it was once a more massive, normal galaxy. It appears to have lost much of its outer material and potentially all of its globular clusters to M31 during a past encounter.12
- Star Streams and Clouds: Deep surveys of the Andromeda Galaxy's outer regions have revealed massive, coherent structures consisting of star streams and clouds. These features are interpreted as the remnants of smaller galaxies that were consumed by M31, alongside stars ejected from the main galaxy due to the intense tidal forces generated during these collisions.12
These findings support the broader understanding in cosmology that galaxies are not static entities but evolve through the ongoing process of merging with smaller systems.2