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What evidence shows that the Andromeda Galaxy absorbed smaller galaxies?
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Galaxy
The Whirlpool Galaxy (left), also known as M51, an Sc galaxy accompanied by a small irregular companion galaxy, NGC 5195 (right).
Evidence indicates that the Andromeda Galaxy has a history of absorbing smaller galaxies through collisions and accretion. Key findings include:
- Stellar Structures: Deep surveys of Andromeda’s outer regions have revealed massive, coherent structures consisting of star streams and clouds. These are identified as the remnants of smaller galaxies that were consumed by the central galaxy, alongside stars ejected from Andromeda itself due to intense tidal forces.12
- Companion Galaxy M32: The structure of M32, a close companion to Andromeda, suggests it was once a more massive, normal galaxy. It appears to have lost its outer layers and potentially all of its globular clusters to Andromeda during a past encounter.12
These observations support the broader understanding that large galaxies grow over time by merging with and accreting smaller neighboring systems.2