Hidden in this deep sky image (left) is Uma3/U1, a miniscule group of stars (right) bound together by their own gravity (and possibly even dark matter!) in orbit around the Milky Way. Credit: CFHT/S. Gwyn (right) / S. Smith (left)

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

A team of astronomers led by the University of Victoria and Yale University has discovered the faintest and least massive Milky Way satellite ever discovered, an ancient planet orbiting our galaxy called Ursa Major III/UNIONS 1 (UMa3/U1). discovered a star system. And it’s probably one of the most dark matter-dominated systems we know of. The research team conducted the study from Hawaii using two Mauna Kea observatories on the Big Island: the W.M. Keck Observatory and the Canada-French-Hawaii Telescope (CFHT) and the University of Hawaii Institute for Astronomy Pan-STARRS (Panorama Survey Telescope). did. Haleakale Rapid Response System, Maui). The results were published in the latest issue of the Astrophysical Journal. “UMa3/U1 is located in the constellation Ursa Major (Great Bear), home of the Big Dipper. “Relatively speaking, it’s in the backyard of the universe, about 30,000 light-years from the sun,” says Simon Smith, a PhD student in astronomy at the University of Victoria and lead author of the study. “UMa3/U1 previously evaded detection due to its extremely low luminosity.” Observations show that this system is extremely small, containing only about 60 stars that are more than 10 billion years old and only 10 light-years in diameter. UMa3/U1’s mass is extremely small, 16 times that of our Sun, and 15 times smaller than the dimmest dwarf galaxy. UMa3/U1 was first discovered using data from the CFHT and Pan-STARRS Ultraviolet Near Infrared Optical Northern Survey (UNIONS). The team then used Keck Observatory’s Deep Imaging Multi-Object Spectrometer (DEIMOS) to examine the system in more detail and confirm that UMa3/U1 is a gravitationally bound system, i.e. a dwarf galaxy or star cluster. did. “UMa3/U1 has such a small number of stars that one might wonder if this is just a random grouping of similar stars.” Keck argues that this is not the case. ,” says co-author Mara Geha, a professor of astronomy. He then studied physics at Yale University. “Our DEIMOS measurements clearly show that all stars move through space at very similar speeds and appear to have similar chemical properties.” “Interestingly, preliminary velocity distributions among the stars in this system may support the conclusion that UMa3/U1 is a dark matter-dominated galaxy. This intriguing possibility will be explored in further Keck observations. ,” said Will Cerny, a Yale graduate student and second author of the study. It’s remarkable how these stars were able to maintain a tight-knit group. One possible explanation is that dark matter may be holding them together. “This object is so small that its long-term survival is quite surprising.” That would have been the case,” Cerny said. “The fact that this system appears to be intact raises two equally interesting possibilities.” Either UMa3/U1 is a small galaxy stabilized by a large amount of dark matter, or it’s ours. Either they are star clusters that can be combined into one. It was a very special moment before his imminent death. ” Under the former scenario, direct confirmation that UMa3/U1 is a satellite system dominated by faint, ancient dark matter would be interesting because it would confirm the predictions of leading theories about the origin of the universe. It will be a success. Using the lambda cold dark matter (LCDM) model, scientists believe that galaxies like the Milky Way generate gravitational forces as they form, which attracts hundreds of satellite systems that continue to orbit the galaxy today. ing. A related study on the impact of UMa3/U1 on LCDM theory has been accepted for publication in the Astrophysical Journal and is available in preprint format at arXiv.org. “Whether future observations confirm or refute the existence of large amounts of dark matter in this system, we believe this object may be the tip of the iceberg, meaning this is the first.” “We’re very excited about the possibility that it could be an example of an extremely faint star system that has so far eluded discovery,” Cerny said. Conclusive evidence of the presence of dark matter in UMa3/U1 is key to determining whether this system is a dwarf galaxy or a star cluster. Until the classification is clear, Ursa Major III / UNIONS 1 has two names: Ultrafaint Milky Way satellites are usually named after the constellation in which they were discovered (in this case Ursa Major), and ultrafaint star clusters are usually named after the research project (UNIONS) in which they were discovered . Although the identity of this star system is still unknown, UMa3/U1 opens the way to new perspectives in cosmology.

source: https://iopscience.iop.org/article/10.3847/1538-4357/ad0d9f