Hiding in Plain Sight: Undergraduates Discover the Densest Galaxies Known

Reconstructed spectrum of light from the ultracompact galaxies M59-UCD3, as seen by the SOAR telescope (top) and M85-HCC1, as seen by the Sloan Digital Sky Survey (bottom). Dark bands are the fingerprints of atoms and molecules in the atmospheres of the stars in the galaxy. These bands reveal the compositions and ages of the stars as well as the velocities of the galaxies.