By measuring the velocities of 8,000 galaxies, corrected for cosmic expansion, a group of astronomers have made the best measurement of the supercluster of galaxies that dominates our region of the cosmos. The researchers, led by Brent Tully of University of Hawaii, tracked galaxies that are flowing in the same direction, much as a watershed includes all water flowing into the same tributary. Such flows offer a novel way to infer the presence of matter by its gravitational pull, whether or not it is visible. Earth and the Milky Way were previously considered part of the Virgo supercluster, which now appears to be just one region of a much greater structure called Laniakea-"immeasurable heaven" in Hawaiian. The Laniakea supercluster measures 500 million light-years across and contains the mass of about 100 quadrillion suns. This work is part of an ongoing conversation in cosmology on how to map and define the large-scale structure of the universe.
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