Surprise ‘fossil galaxy’ spotted near mighty Andromeda

An amateur astronomer has found a fossilized surprise in the well-studied skies near the bright Andromeda Galaxy.

Skywatcher Giuseppe Donatiello spotted an ultra-faint dwarf galaxy, now dubbed Pegasus V, in archival data from a US Department of Energy camera designed to hunt dark energy. Intrigued astronomers who heard of his observations then studied the area using a larger Hawaiian telescope, called the Gemini North. Scientists now think that Pegasus V could be a “fossil” of the first galaxies, stuffed with very old stars.

“This discovery marks the first time such a faint galaxy has been discovered around the Andromeda Galaxy using an astronomical survey that was not specifically designed for this task,” said astronomer Michelle Collins. at the University of Surrey in the UK who led the new research, said in a statement (opens in a new tab) from the National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab), which operates Gemini North.

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Pegasus V (in circle) is an ultra-faint dwarf galaxy located on the edge of the famous Andromeda galaxy, M31. The discovery was announced on June 30, 2022. (Image credit: International Gemini Observatory/NOIRLab/NSF/AURA Acknowledgment: Image processing: TA Rector (University of Alaska Anchorage/NSF’s NOIRLab), M. Zamani (NSF’s NOIRLab) & D. de Martin (NSF’s NOIRLab))

The galaxy was first detected in data collected by the Víctor M. Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile. Donatiello was participating in a search for the dwarf galaxies of Andromeda led by David Martinez-Delgado of the Instituto de Astrofísica de Andalucía, Spain, when his keen eyes spotted Perseus V.

The new discovery, which contains only very small amounts of heavy elements, must therefore be a particularly old galaxy, the scientists say.

Finding such an object is critical because astronomers expect many faint galaxies to exist but have actually observed very few. Scientists aren’t sure why this discovery gap for these faint, fossilized galaxies might exist, though their faint glow certainly makes them hard to spot, even by professionals.

But if future research proves relatively empty, astronomy could face a judgment call. “If there are really fewer faint galaxies than expected, this would imply a serious problem with astronomers’ understanding of cosmology and dark matter,” NOIRLab said.

The Andromeda Galaxy, close to where the faint new galaxy was discovered, sits on the edges of the Andromeda constellation. (Image credit: Alan Dyer/VW PICS/Universal Images Group via Getty Images)

Dark matter is thought to make up much of the underlying structure of the universe, but the challenge astronomers face in their search is that dark matter is invisible to telescopic surveys. We can only see it through its effects on other objects.

The hope is that the keen eyes of NASA’s James Webb Space Telescope will shed more light on early galaxies when this deep-space observatory goes live in mid-July.

“This tiny fossil galaxy from the early universe can help us understand how galaxies form and whether our understanding of dark matter is correct,” Collins said.

A pre-printed version of the study is available at (opens in a new tab). The study will appear shortly in the monthly peer-reviewed notices of the Royal Astronomical Society, according to NOIRLab.

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