A previously unknown dwarf galaxy has been discovered on the outskirts of the Andromeda Galaxy, adding to the growing list of mysterious satellite galaxies lurking in our cosmic neighborhood. Named Pegasus VII, this newly identified low-luminosity galaxy is one of the faintest Andromeda satellites ever detected, suggesting that many more galaxies may be hiding in the shadows of larger cosmic structures. This discovery not only expands our understanding of galaxy formation but also raises intriguing questions about how these small, ancient stellar systems interact with their giant galactic hosts.
A Hidden Galaxy Uncovered in Deep Space
A new study published on February 13, 2025, on the arXiv preprint server details the discovery of Pegasus VII, a dwarf galaxy located 2.4 million light-years away. The research, led by Simon E. T. Smith from the University of Victoria, Canada, used data from the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) to detect an unusual stellar overdensity in the halo of Andromeda (Messier 31).
Follow-up imaging from the Canada-France-Hawaii Telescope and Gemini-North Telescope confirmed that Pegasus VII is a true dwarf galaxy, not just a faint star cluster. The study revealed that Pegasus VII is just now approaching the Andromeda Galaxy, meaning it has likely remained isolated for billions of years before being drawn into Andromeda’s gravitational influence.
A Faint and Ancient Remnant of the Early Universe
Dwarf galaxies are among the oldest structures in the universe, serving as fossil records of the earliest star-forming epochs. Pegasus VII is no exception—it has been estimated to be around 10 billion years old, meaning it has existed since the early days of galaxy formation.
Despite its age, Pegasus VII is extremely faint, with an absolute magnitude of −5.7 and a stellar mass of only 26,000 solar masses. For comparison, this makes it five times larger than the biggest known globular clusters in Andromeda, yet it is still one of the smallest and faintest galaxies ever discovered.
The study also found that Pegasus VII is elongated, with an ellipticity of 0.5—a possible sign that it has already experienced gravitational interactions with Andromeda. This means that Pegasus VII may be slowly being stretched and distorted as it falls into Andromeda’s orbit.
What Makes Pegasus VII Unique?
While many dwarf galaxies have been found in the halo of Andromeda, Pegasus VII stands out for several reasons:
- It is one of the faintest Andromeda satellites ever discovered, indicating that many more may still be undetected.
- It is just beginning to enter Andromeda’s gravitational pull, providing a rare snapshot of a dwarf galaxy before it merges with a larger host.
- Its stellar population and chemical composition suggest that it has been largely untouched for billions of years, making it an excellent laboratory for studying ancient star formation.
A Growing Population of Hidden Galaxies
The discovery of Pegasus VII supports the idea that many more dwarf galaxies remain undiscovered around Andromeda and the Milky Way. These galaxies are difficult to detect because of their low brightness and small size, but advanced surveys like UNIONS are helping astronomers spot these hidden structures.
“The discovery of Pegasus VII complements both the empirical and theoretical claim that a wealth of dwarf galaxy satellites remain undetected towards M31,” the study states. This means that in the coming years, we may uncover even more small galaxies, shedding light on how large galaxies like Andromeda grow by absorbing smaller companions.
