Detection plot for Ursa Major III/UNIONS 1. Projected sky positions in the tangent plane of all stars in a 12′ × 12′ region around the overdensity. Credit: arXiv (2023). DOI: 10.48550/arxiv.2311.10147
By analyzing images from the Ultraviolet Near Infrared Optical Northern Survey (UNIONS), an international team of astronomers discovered a new compact satellite of the Milky Way, which received the designation Ursa Major III/UNIONS 1. The new discovered object turns out to be the faintest known satellite of the Milky Way. The discovery is reported in a paper published November 16 on the preprint server. arXiv.
The Milky Way is known to be surrounded by dozens of smaller, gravitationally bound galaxies or star clusters. Although the list of identified satellites is relatively long, astronomers believe that some dwarf and faint galaxies remain undetected.
One of the astronomical studies capable of detecting such satellites is UNIONS, which observes the sky over 4,800 square degrees in the northern hemisphere. This is a collaboration between two Hawaiian observatories: the Canada-France-Hawaii Telescope (CFHT) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). One of the main goals of the survey is to study the assembly and structure of the Milky Way.
A team of astronomers led by Simon ET Smith from the University of Victoria in Canada studied the UNIONS data as part of the search for new galaxies in the Local Group. As a result, they found the satellite of the Milky Way, which was not reported by previous studies.
“Ursa Major III/UNIONS 1 (UMa3/U1) was discovered during an ongoing search for weak local group systems in UNIONS,” the researchers wrote.
The team initially identified Ursa Major III/UNIONS 1 as a spatially resolved star overdensity in the UNIONS data. Then they obtained radial velocities from the Keck telescope and the proper motions from ESA’s Gaia satellite, which confirmed that it is a coherent system.
Ursa Major III/UNIONS 1 has an absolute total V-band magnitude of +2.2 mag, making it the faintest Milky Way satellite detected so far. The previous record holder was Kim 3, an ultra-faint star cluster with a total V-band absolute magnitude of +0.7 mag.
According to the article, Ursa Major III/UNIONS 1 is very compact because it has a half-light radius of about 10 light years and contains only about 50 to 60 stars. Its total mass is therefore also estimated to be very low: around 16 solar masses.
The results indicate that Ursa Major III/UNIONS 1 has a pericenter of 41,700 light years and crosses the disk of the Milky Way about 52,100 light years from the galactic center. The data also suggests that Ursa Major III/UNIONS 1 is at least 11 billion years old and has a metal-poor stellar population.
Regarding the origin and nature, Ursa Major III/UNIONS 1 could have been accumulated in the Milky Way halo and could be a dwarf galaxy or star cluster. Therefore, follow-up observations are necessary in order to reveal the true nature of this compact and weak satellite.
More information:
Simon ET Smith et al, The discovery of the Milky Way’s faintest known satellite using UNIONS, arXiv (2023). DOI: 10.48550/arxiv.2311.10147
Journal information:
arXiv
© 2023 Science X Network
Quote: Astronomers discover the Milky Way’s faintest satellite (November 27, 2023) retrieved November 28, 2023 from
This document is subject to copyright. Except for fair use for private study or research purposes, no part may be reproduced without written permission. The content is provided for information only.
