The faintest known star system orbiting the Milky Way has been discovered  Urania

A team of astronomers has discovered an ancient star system traveling around our galaxy, the faintest and least massive Moon of the Milky Way ever discovered.

The team conducted the research from Hawaii using the Maunakea Observatories as well as the University of Hawaii Institute of Astronomy. Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) in Haleakala, Maui; the findings published Th Astrophysical Journal.

The UMa3/U1 system is located towards the constellation Ursa Majorhouse Big Dipper. It is located in our cosmic backyard, at a distance of about 30,000 km Light year from the sun said Simon Smith, an astronomy graduate student at the University of Victoria and lead author of the study. UMa3/U1 has been eluded to be detected until now due to its extremely low brightness.

Observations have shown that the star system is small, consisting of only about 60 stars older than 10 billion years, and spanning only 10 light-years. UMa3/U1 has an extremely low mass – 16 times smaller than the mass of the Sun, and therefore 15 times smaller than the faintest known mass. Dwarf galaxy.

UMa3/U1 was first discovered using data from Ultraviolet-Near-Infrared Optical Northern Survey (UNIONS) CFHT and Pan-STARRS.

The team then examined the star system in more detail using… Deep Imaging Multi-Object Spectrometry (DEIMOS) Keck confirmed that UMa3/U1 is a gravitationally bound system, or a dwarf galaxy Star cluster.

There are so few stars in UMa3/U1 that one might reasonably doubt whether it is just a random collection of similar stars. Keck was instrumental in showing that this was not the case said co-author Marla Geha, a professor of astronomy and physics at Yale University. DEIMOS measurements clearly show that all stars move through space at very similar speeds and appear to have similar chemical compositions.

Interestingly, the uncertain velocity distribution between stars in the system may support the conclusion that UMa3/U1 is a galaxy dominated by Dark matter This is a tantalizing possibility that we hope to explore further in Keck's notes – said Will Cerny, the second author of the study and a graduate of Yale University.

The way these stars manage to keep their group together is amazing. One possible explanation is that dark matter may be holding them together.

The body is so small that its long-term survival is quite surprising. One would expect strong tidal forces to originate from the disk milky way They will shred the system, leaving no noticeable residue Cerny said. The fact that the system appears sound leads to two equally interesting possibilities. Either UMa3/U1 is a small galaxy settled with large amounts of dark matter, or it is a star cluster that we observed at a very specific moment before its inevitable demise.

In the first scenario, obtaining direct confirmation that UMa3/U1 is an ancient, faint star system would be a very exciting development, because it would confirm predictions made in the main theory about the origin of the universe. According to the model Lambda cold dark matter (Λ-CDM)Scientists hypothesize that when galaxies like the Milky Way first formed, they created a gravitational force during their formation, attracting hundreds of space star systems that still orbit these galaxies.

A companion study on the effects of UMa3/U1 on Λ-CDM theory has been accepted for publication in The Astrophysical Journal and is now in press. Accessible In pre-print format on

Whether future observations confirm or deny that this system contains a significant amount of dark matter, we are very excited by the prospect that this object may be the tip of the iceberg — that it may be the first example of a new class of extremely faint star systems whose pores have not yet been discovered. Cerny said.

Conclusive evidence of the presence or absence of dark matter in UMa3/U1 is key to determining whether this star system is a dwarf galaxy or a star cluster. Until its classification is clarified, Ursa Major III/UNIONS 1 operates under two names. It is usually very weak Space galaxies The Milky Way is named after the constellation in which it was discovered (in this case Ursa Major), while very faint star clusters are usually named after the research project in which they were identified (here UNIONS).

Although the identity of this star system remains a mystery, UMa3/U1 paves the way for new perspectives in cosmology.

This discovery could challenge our understanding of galaxy formation and perhaps even the definition of…Galaxies Smith said.

Agnieszka Novak

more information:

Source: Keck Observatory

Pictured: Hidden in this deep-sky image (left) is UMa3/U1, a small cluster of stars (right) held together by their own gravity (and perhaps dark matter!) in orbit around the Milky Way. Source: CFHT/S. Gwen (right)/S. smith (left)

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