Scientists have proposed that a hidden ancient dwarf galaxy, named “Loki”, lies inside the Milky Way. A dwarf galaxy is a small galaxy with fewer stars and lower mass than large galaxies such as the Milky Way. The team studied 20 old, metal-poor stars within 2 kiloparsecs of the Sun using spectroscopy. These stars showed both prograde and retrograde motion, meaning some move with and some against the Milky Way’s rotation. The study used ESPaDOnS, a high-resolution spectropolarimeter, to examine chemical elements created in supernovae and neutron star mergers.