Like a silent congregation of stealth gemstones, astronomers have discovered a gigantic galaxy lurking right outside the Milky Way's front door. Researchers at the University of Cambridge submitted a recent report in the Monthly Notices of the Royal Astronomical Society introducing humanity to the Crater 2 ultra-dwarf galaxy, an extremely dim and dark galaxy determined to be one of the feeblest, faintest galaxies ever spotted in the universe. Now nicknamed “the feeble giant,” this fantastic collection of stars just around the cosmic corner has somehow escape detection despite being in such close proximity to the Milky Way. It's cataloged as the fourth largest satellite of the Milky Way, surpassed only by the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) and the Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph).
One of the main reasons for its secret existence is that it falls under the nominal detection boundary in sky surveys and compares in relative obscurity to the recently discovered Tuc 2 and Tuc IV and UMa II. Crater 2 is 391,000 light-years from the sun and officially measures 3,500 half-light years across. It appears to be in alignment with the globular cluster Crater, the pair of ultra-faint dwarf galaxies Leo IV and Leo V, and the dwarf galaxy Leo II. Dwarf galaxies have no clear boundaries due to the density of their stars gradually decreasing toward the outer borders, so they're measured by their half-light radius, the distance from their observed center.
Possibly formed by a series of galactic mergers, Crater 2 should give scientists a clearer window into the evolution of the Milky Way, and its discovery allows for the possibility that a healthy number of extremely low surface brightness dwarf galaxies may still be out there somewhere in the darkness.