Starship Asterisk*

Fritz Zwicky, famous American astronomer of Swiss origin, arrived in 1933 at the astonishing conclusion that even though galaxies are the signposts of galaxy clusters their contribution to the total cluster mass is minuscule in comparison to a dominant dark matter component. Current estimates of a cluster total mass indicate that the contributions roughly are: galaxies 1%, hot intracluster gas 9%, and dark matter the remaining 90%. Until now these systems, megaparsec in size and with up to hundreds of trillions of solar masses, were easily recognized in visible light because of the brightness of the embedded galaxies and their concentration towards the cluster centers. Because of their large masses and extent, clusters of galaxies are fundamental to the mapping and mass budget of the universe. New work by an international team of scientists suggests that perhaps as many as a third of all clusters have previously been missed. The study, conducted in the nearby universe, showed that the newly revealed clusters contain fewer, less packed, and less luminous galaxies, in comparison to the conventional clusters.

The discovery was made using public data for 191,440 galaxies from a major galaxy redshift survey (the "2dFGRS") conducted a decade ago with a robotic instrument at the 3.9-meter Anglo-Australian Telescope. The re-examination of the data ("Data-mining") through a computer-based procedure developed by this team, together with the abandonment of prejudices on the clusters' appearance, conducted to the reported discovery. ...

• Astrophysical Journal 869(2):145 (2018 Dec 20) DOI: 10.3847/1538-4357/aaeff3