Rubin Observatory Detects Aquarius IV, a Faint Milky Way Satellite

Scientists using Rubin Observatory’s Early Data Preview 2 have announced Aquarius IV, an ultra-faint Milky Way satellite about 355,000 light-years away with an apparent magnitude of 18.3. The object was first spotted in Rubin data and later confirmed in archival images from the Dark Energy Camera, illustrating Rubin LSST’s potential to uncover many more faint satellites. Whether Aquarius IV is truly an ultra-faint dwarf galaxy or an unusually large globular cluster remains provisional, pending further spectroscopy and peer review.