A team of astronomers led by the University of Victoria (Canada) and Yale University (US) has discovered an ancient star system orbiting our Milky Way Galaxy – the faintest and lightest Milky Way satellite ever detected. The tiny galaxy designated UMa3/U1 is located in the well-known constellation Ursa Major and is about 30,000 light-years away from us. Observations show that UMa3/U1 consists of about sixty stars that are more than 10 billion years old and are only about 10 light-years in size. All told, it has only sixteen times the mass of the Sun.
UMa3/U1 was first spotted in data from the Ultraviolet Near Infrared Optical Northern Survey, conducted with the Canada-France-Hawaiʻi Telescope and Pan-STARRS. The astronomers then examined the galaxy in more detail using the Deep Imaging Multi-Object Spectrograph (DEIMOS) at the Keck Observatory. In this way they were able to confirm that UMa3/U1 is held together by gravity. That means it is a dwarf galaxy or star cluster.
It is unclear how these stars managed to remain a close group. The object is so small that you would expect the strong tidal forces of our Milky Way Galaxy to have already torn the star system apart and leave no discernible remnant. The fact that the galaxy appears intact leads to two equally interesting possibilities: either UMa3/U1 is a tiny galaxy stabilized by large amounts of dark matter, or it is a star cluster discovered by chance shortly before its demise.
In the first case, the existence of UMa3/U1 would support a prediction of the most common theory of the origin of the universe. According to this Lambda Cold Dark Matter (LCDM) model, galaxies like the Milky Way must have accumulated satellite galaxies around them during their formation that continue to orbit them to this day. (EE)
Faintest Known Star System Orbiting The Milky Way Discovered From Hawaii
