Shulou(Shulou.com)12/24 Report--

CTOnews.com, November 30 (Xinhua) an international team of astronomers has discovered the darkest satellite galaxy in the Milky way by analyzing the image data of the Ultraviolet near Infrared Optical Northern Sky Survey (UNIONS) and named it Ursa Major III / UNIONS 1.

Satellite galaxies are galaxies that surround another large galaxy under the influence of gravity. Galaxies are made up of a large number of celestial bodies, and although they are not directly connected to each other, they have a center of mass that represents the average position of all masses.

At present, the consensus in the industry is that the Milky way is surrounded by dozens of smaller gravitationally bound galaxies or star clusters. Although the established list of satellites is relatively long, astronomers believe that some dwarf and dim galaxies have not yet been discovered.

The UNIONS project, which consists of the Canada-France-Hawaii Telescope (CFHT), the panoramic Survey Telescope and the Rapid response system (Pan-STARRS), observes the sky above 4800 square degrees in the Northern Hemisphere. One of the main objectives is to investigate the composition and structure of the Milky way.

The international team, led by Simon Smith of the University of Victoria in Canada, found the lowest known bright satellite in the Milky way after delving into UNIONS data.

The team used data provided by the Keck telescope to determine the satellite's radial velocity and the ESA's Gaia satellite to determine the satellite's motion aggregation.

The absolute magnitude of Ursa Major III / UNIONS 1 is + 2.2 mag, which makes it the darkest satellite in the Milky way detected so far.

The paper says that Ursa Major III / UNIONS 1 is very compact, with a radius of about 10 light-years, contains only 50-60 stars, and their total mass is very low, 16 times that of the sun.

CTOnews.com attached the address of the reference paper: Simon E. T. Smith et al, The discovery of the faintest known Milky Way satellite using UNIONS, arXiv (2023). DOI: 10.48550/arxiv.2311.10147

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