... Tonight's Sky . ... Observing . ... Gravitational wave search provides insights into galaxy evolution and mergers . ... galaxies . ... Sky Guide . ... Dense galaxies hiding in plain sight . ... Two ultra-dense galaxies (insets) have been discovered orbiting larger host galaxies. ... However, they were overlooked for decades because no one imagined such objects existed: they were hiding in plain sight, said Richard Vo. ... Only registered members of Astronomy.com are allowed to comment on this...