Unusual fossil galaxy discovered on the outskirts of Andromeda may reveal the history of the universe

Ultra-Faint Dwarf Galaxy Pegasus V
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The Gemini North telescope shows a relic of the earliest galaxies.

A unique, ultra-faint dwarf galaxy has been discovered on the outer fringes of the Andromeda Galaxy thanks to the insightful eye of an amateur astronomer studying archival data processed by the NSF NOIRLab Center for Social Science and Data. It turned out that the dwarf galaxy Pegasus V contains very few heavy elements and is probably a fossil of the first galaxies in f.follow-up observations by professional astronomers using the International Gemini Observatory, NSF’s NOIRLab program.

An unusual ultra-faint dwarf galaxy has been detected at the edge of the Andromeda Galaxy with the help of several National Science Foundation NOIRLab facilities. Named Pegasus V, the galaxy was first discovered as part of a systematic search for Andromeda dwarfs coordinated by David Martínez-Delgado of the Institute of Astrophysics of Andalusia, Spain, when amateur astronomer Giuseppe Donatiello discovered a curious “spot” in the data in[{” attribute=””>ДЕЗИ Изображение Legacy Imaging Surveys.” width=”777″ height=”396″ srcset=”” sizes=”” ezimgfmt=”rs rscb1 src ng ngcb1 srcset” loading=”eager” importance=”high”/>

Изображение было получено с помощью камеры темной энергии, изготовленной Министерством энергетики США, на 4-метровом телескопе Виктора М. Бланко в Межамериканской обсерватории Серро-Тололо (CTIO). Данные были обработаны через Community Pipeline, которым управляет Центр науки и данных сообщества NOIRLab (CSDC).

Faint stars in Pegasus V were discovered in subsequent deeper observations by astronomers using the larger 8.1-meter Gemini North telescope with the GMOS instrument, confirming that it is an ultra-faint dwarf galaxy on the outskirts of the Andromeda Galaxy. Gemini North in Hawaii is half of the International Gemini Observatory.

Observations with Gemini have shown that this galaxy is extremely low in heavy elements compared to similar dwarf galaxies, meaning it is very old and likely a fossil of the first galaxies in the universe.

“We have discovered an extremely dim galaxy whose stars formed very early in the history of the universe,” commented Michelle Collins, an astronomer at the University of Surrey, UK, and lead author of the paper announcing the discovery. “This discovery marks the first time that such a dim galaxy has been detected around the Andromeda Galaxy by an astronomical survey that was not specifically designed for this task.”

The ultra-faint dwarf galaxy Pegasus V

A unique, ultra-faint dwarf galaxy has been discovered on the outer fringes of the Andromeda Galaxy thanks to the keen eye of an amateur astronomer studying archival data from the US Department of Energy’s Dark Energy Camera on the 4-meter Victor M. Blanco Telescope. Telescope at Cerro Tololo Inter-American Observatory (CTIO) and processed by the Social Science and Data Center (CSDC). Follow-up observations by professional astronomers with the International Gemini Observatory have shown that the Pegasus V dwarf galaxy contains very few heavy elements and is likely a fossil of the first galaxies. All three entities involved are NOIRLab NSF programs. Credit & Copyright: International Gemini Observatory/NOIRLab/NSF/AURA. Acknowledgment: Image Processing: TA Chancellor (University of Alaska Anchorage/NOIRLab NSF), M. Zamani (NOIRLab NSF), and D. de Martin (NOIRLab NSF)

The faintest galaxies are thought to be fossils of the very first galaxies to form, and these galactic relics hold clues about the formation of the earliest stars. While astronomers expect the universe to be teeming with faint galaxies like Pegasus V,[2] they have yet to discover almost as much as their theories predict. If there are indeed fewer faint galaxies than predicted, this will mean a serious problem with astronomers’ understanding of cosmology and dark matter.

Thus, finding examples of these faint galaxies is important, but also difficult. Part of the problem is that these dim galaxies are extremely difficult to spot, as they look like a few rare stars hidden in vast sky images.

“The problem with these extremely faint galaxies is that they have very few of the bright stars that we normally use to identify them and measure their distances,” said Emily Charles, a University of Surrey PhD student who also took part in the study. . “The 8.1-meter Gemini mirror allowed us to find faint old stars, which allowed us to measure the distance to Pegasus V and determine that its stellar population is very old.”

The strong concentration of old stars the team found in Pegasus V suggests the object is likely a fossil of the first galaxies. Compared to other faint galaxies around Andromeda, Pegasus V appears to be uniquely old and metal-poor, indicating that its star formation did indeed cease very early.

“We hope that further study of the chemical properties of Pegasus V will provide a clue to understanding the earliest periods of star formation in the universe,” Collins concluded. “This small fossil galaxy from the early universe could help us understand how galaxies form and whether our understanding of dark matter is correct.”

“The Gemini North public telescope provides many opportunities for community astronomers,” said Martin Still, Gemini Program Manager at the National Science Foundation. “In this case, the Gemini supported this international team to confirm the presence of the dwarf galaxy, physically link it to the Andromeda Galaxy, and determine the metal deficiency in its evolved stellar population.”

Future astronomical objects should shed more light on faint galaxies. Pegasus V witnessed a period in the history of the universe known as reionization, and other objects dating back to this time will soon be observed by NASA’s James Webb Space Telescope. Astronomers also hope to discover other such faint galaxies in the future using the Vera S. Rubin Observatory, the National Science Foundation’s NOIRLab program. The Rubin Observatory will conduct an unprecedented ten-year survey of the optical sky called the Legacy Survey of Space and Time (LSST).


  1. The DESI Legacy Imaging Surveys were conducted to define targets for Dark Energy Spectroscopic Instrument (DESI) operations. These surveys are a unique combination of three projects that observed a third of the night sky: The Legacy Dark Energy Camera (DECaLS), observations with the Department of Energy Built Dark Energy Camera (DECam) on the 4-meter Victor M. Blanco Telescope. Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile; Mayall’s legacy z-band survey (MzLS) with the Mosaic3 camera on the 4-m Nicholas W. Mayall Telescope at Kitt Peak National Observatory (KPNO); and the Beijing-Arizona Sky Survey (BASS) with the 90Prime camera on the 2.3-meter Bok Telescope, owned and operated by the University of Arizona and located at KPNO. CTIO and KPNO are NOIRLab NSF programs.
  2. Pegasus V is so named because it is the fifth dwarf galaxy discovered, located in the constellation Pegasus. The distance between Pegasus V and the Andromeda galaxy in the sky is about 18.5 degrees.

Additional Information

This research was presented in a paper titled “Pegasus V is a newly discovered ultra-faint dwarf galaxy on the outskirts of Andromeda.” Royal Astronomical Society Monthly Notices.

Reference: “Pegasus V – A newly discovered ultra-faint dwarf galaxy on the outskirts of Andromeda” Michelle L. M. Collins, Emily J. E. Charles, David Martinez-Delgado, Matteo Monelli, Noushin Karim, Giuseppe Donatiello, Eric J. Tollerud, and Walter Boskin . , Received, Royal Astronomical Society Monthly Notices.
archive: 2204.09068

The group includes Michelle L. M. Collins (Department of Physics, University of Surrey, UK), Emily J. E. Charles (Department of Physics, University of Surrey, UK), David Martínez-Delgado (Institute of Astrophysics of Andalusia, Spain), Matteo Monelli (Instituto de Astrofísica de Canarias (IAC) and Universidad de La Laguna, Spain), Noushin Karim (Department of Physics, University of Surrey, UK), Giuseppe Donatiello (UAI – Unione Astrofili Italiani, Italy), Eric J. Tollerud (Space Science) Telescope Institute, USA), Walter Boskin (Institute of Astrophysics of the Canary Islands (IAC), University of La Laguna and Fundación G. Galilei – INAF (Telescopio Nazionale Galileo), Spain).

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