Should they be called galaxies then?
Engineers have outfitted the National Science Foundation’s (NSF) Arecibo Observatory telescope with a new instrument that could help it discover galaxies that have no stars – so called “dark galaxies”. The instrument is called ALFA (for Arecibo L-Band Feed Array), which is essentially a seven-pixel digital camera, which allows the radio telescope to receive data seven times as fast. Researchers will explore groups of galaxies, and determine how fast they’re converting gas into stars. It should be able to discover if there are gas-rich regions, invisible to optical telescopes, which can be detected by their hydrogen signature.
– Universe Today