Images of the open dwarf galaxies taken by the Magellanic Telescope and Hubble. Credit: Burçin Mutlu-Pakdil et al. / arXiv: 2108.09312v1

Hubble Spots 3 “Fossil” Galaxies from Early Universe–10 Things You Need To Know

The three new dwarf galaxies are among the dimmest systems found outside the Local Group to date.

Astronomers using the Hubble Space Telescope have discovered three new ultra-low dwarf galaxies that are satellites of the large spiral galaxy NGC 253. Their study is expected to help understand the mechanisms of formation and evolution of galaxies and the role of dark matter in them.

Everything you need to know about dwarf galaxies and their importance for science

What are dwarf galaxies?

Dwarf galaxies are among the most common star systems in the universe. The study of the dimmest and least massive representatives of this class of galaxies helps scientists understand the nature of dark matter and the mechanisms of galaxy formation.

Dominated by dark matter

That is because ultra-faint dwarf galaxies are the ones that are mostly dominated by dark matter. At the same time, they are less chemically evolved than galaxies like the Milky Way, for example.


In particular, two problems of the accepted cosmological model of ΛCDM are associated with dwarf galaxies: the problem of the deficit of dwarf galaxies and the TBTF problem (Too Big To Fail).

More detailed tests

New and more detailed tests of the ΛCDM model require new observational data from dwarf galaxies, not only those associated with the Milky Way but others in the Local Group or beyond.

The area around the galaxy NGC 253, explored within the PISCeS program. Snapshot from DSS survey. Previously discovered dwarf galaxies are marked with blue circles, new ones - with red ones. Credit: Burçin Mutlu-Pakdil et al. /
The area around the galaxy NGC 253, explored within the PISCeS program. Snapshot from DSS survey. Previously discovered dwarf galaxies are marked with blue circles, new ones – with red ones. Credit: Burçin Mutlu-Pakdil et al. /

Three new dwarf galaxies

A group of astronomers led by Burçin Mutlu-Pakdil of the University of Chicago reported the discovery of three new ultra-low dwarf galaxies associated with spiral galaxy NGC 253 (Sculptor Galaxy), which is the brightest in the Sculptor group (adjacent to the Local Group) and located in the distance 11.5 million light-years from the Sun.

Instruments used

The discoveries were made in the framework of the PISCeS (Panoramic Imaging Survey of Centaurus and Sculptor) program; the Hubble Space Telescope and one of the ground-based Magellanic telescopes took part in the observations.


The results of the observations bring the total number of dwarf satellites of NGC 253 discovered by PISCeS to five. All five systems contain mainly an old (∼12 billion years old), metal-poor stellar population, are characterized by low luminosities (M V from −7 to −12), and are comparable to the dwarf galaxies of the Milky Way and the Andromeda Nebula.

Some of the dimmest systems

Three new companion galaxies of NGC 253 are among the dimmest systems found outside the Local Group. Scl-MM-dw3 is the smallest of these, with an effective radius of 362 light-years.

Locations and mass

The galaxy is located 264 thousand light-years from NGC 253 (Sculptor Galaxy), and its stellar mass is 110 thousand solar masses. The mass of Scl-MM-dw4 is comparable to Scl-MM-dw3, but its effective radius is greater – 613 light-years.


The distance between Scl-MM-dw4 and NGC 253 is estimated at about 280.3 thousand light-years. Finally, Scl-MM-dw5 lies 313,000 light-years from NGC 253, has an effective radius of 1167 light-years, and has a stellar mass of about 140,000 solar masses.

Future observations

Scientists believe that many satellite systems may exist at large distances from NGC 253, it is expected that they will be discovered as part of further observations under the PISCeS program.

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Clarke, A. (2021, September 1). NASA’s Hubble Space Telescope Detects ultra Weak Galactic fossils Near Sculptor’s Galaxy. Science Times.
Florida News Times. (2021, August 31). Three new ULTRA-WEAK dwarf galaxies have been discovered.
Mutlu-Pakdil, B., Sand, D. J., Crnojević, D., Jones, M. G., Caldwell, N., Guhathakurta, P., Seth, A. C., Simon, J. D., Spekkens, K., Strader, J., & Toloba, E. (2021, August 20). Hubble space telescope observations of NGC 253 DWARF Satellites: Discovery of three Ultra-faint dwarf galaxies.
Nowakowski, T. (2021, August 31). Three new ULTRA-FAINT dwarf galaxies discovered.

Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. My experience as a freelance writer began in 2018 but I have been part of the Curiosmos family since mid-2020. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

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