M32p
Hypothesized former galaxy merged into Andromeda 2 billion years ago.
Andromeda’s thick disk and most of its halo stars likely came from a long-lost sibling galaxy, now called M32p. This hypothesized former galaxy was once the third or fourth largest member of the Local Group, rivaling the Milky Way and Andromeda themselves, before it collided with Andromeda roughly 2 billion years ago. That merger also triggered a burst of star formation in Andromeda at the time. Astronomers at the University of Michigan proposed M32p’s existence in 2018, noting that its surviving dense core may be the satellite galaxy Messier 32 (M32). M32’s unusual compactness and its own star-formation spike 2 billion years ago fit this picture, as such traits are rare among similarly sized elliptical galaxies. The original galaxy is estimated to have had a stellar mass of about 2.5×10¹⁰ times that of the Sun.
- type
- Hypothesized former galaxy
- stellar_mass
- 2.5×10^10 M☉
- merger_time
- Estimated 2 billion years ago
- previous_rank
- Third or fourth largest in Local Group
- associated_remnant
- Messier 32 (M32)
- described_by
- Scientists at the University of Michigan (2018)
Lore & Background
M32p is hypothesized to have been a large galaxy, a sister to the Milky Way and Andromeda, before being incorporated into the Andromeda Galaxy. The merger is estimated to have occurred 2 billion years ago, and it is thought to have created the thick disc and contributed the majority of the halo stars of Andromeda, as well as triggering a burst of star formation. The former galaxy is likely associated with the Andromeda satellite galaxy Messier 32 (M32), which may be the remains of its dense core.
Reader's Guide
M32p is significant as a hypothesized major building block of the Andromeda Galaxy, explaining key features such as its thick disc, halo stars, and a past burst of star formation. The model, described in 2018 by scientists at the University of Michigan, proposes that M32p was once the third or fourth largest galaxy in the Local Group, a sister to both the Milky Way and Andromeda. Its remnant may be the dense, compact satellite galaxy Messier 32 (M32), whose unusual characteristics—dense compactness and a burst of star formation 2 billion years ago—are explained by this model, as M32 is unlike other similarly sized elliptical galaxies. This merger paradigm helps clarify the formation history of the Andromeda Galaxy and its outskirts, analogous to the Sausage Galaxy's role in the Milky Way's thick disc and halo stars.
Did You Know?
- M32p is hypothesized to have been the third or fourth largest galaxy in the Local Group before merging into Andromeda.
- The merger is estimated to have occurred 2 billion years ago.
- The Andromeda satellite galaxy Messier 32 (M32) may be the remains of M32p's dense core.
- M32p's stellar mass is thought to have been around 2.5×10^10 M☉.
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