Map of superclusters within the nearby universe
, with Laniakea shown in yellow
Video showing in 3D Laniakea and other nearby superclusters of galaxies.
The Laniakea Supercluster (Laniakea, Hawaiian for open skies or immense heaven), is the galaxy supercluster that is home to the Milky Way and approximately 100,000 other nearby galaxies. It was defined in September 2014, when a group of astronomers including R. Brent Tully of the University of Hawaii, Hélène Courtois of the University of Lyon, Yehuda Hoffman of the Hebrew University of Jerusalem, and Daniel Pomarède of CEA Université Paris-Saclay published a new way of defining superclusters according to the relative velocities of galaxies. The new definition of the local supercluster subsumes the prior defined local supercluster, the Virgo Supercluster, as an appendage.
Follow-up studies suggest that the Laniakea Supercluster is not gravitationally bound; it will disperse rather than continue to maintain itself as an overdensity relative to surrounding areas. Although the Laniakea supercluster is an extremely large structure, even larger cosmic structures have been detected.
The alternative name laniakea means 'immense heaven' in Hawaiian, from lani 'heaven', and ākea 'spacious, immeasurable'. The name was suggested by Nawaʻa Napoleon, an associate professor of Hawaiian language at Kapiolani Community College. The name honors Polynesian navigators, who used knowledge of the heavens to navigate the Pacific Ocean.
The Laniakea Supercluster encompasses approximately 100,000 galaxies stretched out over 160 megaparsecs (520 million light-years). It has the approximate mass of 1017 solar masses, or a hundred thousand times that of our galaxy, which is almost the same as that of the Horologium Supercluster. It consists of four subparts, which were known previously as separate superclusters:
The most massive galaxy clusters of the Laniakea Supercluster are Virgo, Hydra, Centaurus, Abell 3565, Abell 3574, Abell 3521, Fornax, Eridanus and Norma. The entire supercluster consists of approximately 300 to 500 known galaxy clusters and groups. The real number may be much larger because some of these are traversing the Zone of Avoidance, an area of the sky that is partially obscured by gas and dust from the Milky Way galaxy, making them essentially undetectable.
Superclusters are some of the universe's largest structures and have boundaries that are difficult to define, especially from the inside. The team used radio telescopes to map the motions of a large collection of local galaxies. Within a given supercluster, most galaxy motions will be directed inward, toward the center of mass. In the case of Laniakea, this gravitational focal point is called the Great Attractor, and influences the motions of the Local Group of galaxies, where the Milky Way galaxy resides, and all others throughout the supercluster. Unlike its constituent clusters, Laniakea is not gravitationally bound and is projected to be torn apart by dark energy.
Although the confirmation of the existence of the Lanikea Supercluster emerged in 2014, early studies in the 1980s already suggested that several of the Superclusters then known might be connected. For example, South African astronomer Tony Fairall stated in 1988 that redshifts suggested that the Virgo and Hydra-Centaurus Superclusters may be connected.
The neighboring superclusters to the Laniakea Supercluster are the Shapley Supercluster, Hercules Supercluster, Coma Supercluster and Perseus-Pisces Supercluster; they are all part of the Pisces-Cetus Supercluster Complex. The edges of the superclusters and Laniakea were not clearly known at the time of Laniakea's definition. Since then, the study of the edges of the supercluster and of structures beyond them has substantially improved.
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