Astronomers have discovered a new ultra-faint dwarf galaxy in the constellation of Pegasus and characterized it using deep imaging with the Gemini Multi-Object Spectrograph (GMOS) instrument on the 8.1-m Gemini North telescope at the International Gemini Observatory.
The newly-discovered dwarf galaxy is located 260,000 parsecs (848,000 light-years) from the Andromeda galaxy in the outskirts of its halo.
Named Pegasus V, the galaxy appears to be extremely deficient in heavier elements compared to similar dwarf galaxies, meaning that it is very old and likely to be a fossil of the first galaxies in the Universe.
“We have found an extremely faint galaxy whose stars formed very early in the history of the Universe,” said Dr. Michelle Collins, an astronomer at the University of Surrey.
“This discovery marks the first time a galaxy this faint has been found around the Andromeda galaxy using an astronomical survey that wasn’t specifically designed for the task.”
The faintest galaxies are considered to be fossils of the very first galaxies that formed, and these galactic relics contain clues about the formation of the earliest stars.
While astronomers expect the Universe to be teeming with faint galaxies like Pegasus V, they have not yet discovered nearly as many as their theories predict.
If there are truly fewer faint galaxies than predicted this would imply a serious problem with astronomers’ understanding of cosmology and dark matter.
Discovering examples of these faint galaxies is therefore an important endeavor, but also a difficult one.
Part of the challenge is that these faint galaxies are extremely tricky to spot, appearing as just a few sparse stars hidden in vast images of the sky.
“The trouble with these extremely faint galaxies is that they have very few of the bright stars which we typically use to identify them and measure their distances,” said Emily Charles, a Ph.D. student at the University of Surrey.
“Gemini’s 8.1-m mirror allowed us to find faint, old stars which enabled us both to measure the distance to Pegasus V and to determine that its stellar population is extremely old.”
“We hope that further study of Pegasus V’s chemical properties will provide clues into the earliest periods of star formation in the Universe,” Dr. Collins said.
“This little fossil galaxy from the early Universe may help us understand how galaxies form, and whether our understanding of dark matter is correct.”
The team’s paper will be published in the Monthly Notices of the Royal Astronomical Society.
Michelle L.M. Collins et al. 2022. Pegasus V — a newly discovered ultra-faint dwarf galaxy on the outskirts of Andromeda. MNRAS, in press; arXiv: 2204.09068
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