Ultra-faint dwarf galaxies (UFDs) are the least luminous known clusters of stars, where
Panoramic Imaging Survey of Centaurus andSculptor (PISCeS) is one of the astronomical surveys that aims to find such faint galaxies. As part of the PISCeS program, a team of astronomers led by Burcin Mutlu-Pakdil from the University of Chicago observed the field around the galaxy NGC 253 using the Hubble Telescope. They looked for interconnected dwarf star systems near it. NGC 253 is located 11.4 million light-years from Earth. It is one of the brightest galaxies outside the Local Group.
photo: Mutlu-Pakdil et al., 2021
Scientists visually examined all the images insearches for spatially compact clusters of stars around NGC 253 and discovered three new UFDs - Scl-MM-dw3, Scl-MM-dw4, and Scl-MMdw5 - in addition to the two known ones discovered in 2014 and 2016. All three galaxies are equally old, with an estimated age of about 12 billion years. According to modern concepts, the observable Universe originated 13.799 ± 0.021 billion years ago.
Among the three galaxies, Scl-MM-dw3 is the smallest. Its elliptical half-radius along the semimajor axis is estimated to be approximately 362 light years.
Astronomers emphasized that the recently discovereddwarfs have luminosities ranging from -7.5 to -7.24 magnitudes, making them one of the faintest galaxies identified outside our Local Group.
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Local group of galaxies - gravitationally bounda group of galaxies with a diameter of 3 megaparsecs (~ 10 million light years) and a mass of about 2 trillion solar masses, including the Milky Way, the Andromeda galaxy (M31) and the Triangle galaxy (M33) and several other small star clusters.