Laniakea: Our Home Supercluster

Analysis of galaxies shows local supercluster to be 100 times larger than previously thought.

The supercluster of galaxies that includes the Milky Way is 100 times bigger in volume and mass than previously thought, a team of astronomers says. They have mapped the enormous region and given it the name Laniakea — Hawaiian for ‘immeasurable heaven’.

Galaxies tend to huddle in groups called clusters; regions where these clusters are densely packed are known as superclusters. But the definition of these massive cosmic structures is vague.

The new study, published in Nature, describes a novel way to define where one supercluster ends and another begins. A team led by Brent Tully, an astronomer at the University of Hawaii in Honolulu, charted the motions of galaxies to infer the gravitational landscape of the local Universe, and redraw its map.

The team used a database that compiles the velocities of 8,000 galaxies, calculated after subtracting the average rate of cosmic expansion. “All these deviations are due to the gravitational pull galaxies feel around them, which comes from mass,” says Tully. The researchers used an algorithm to translate these velocities into a three-dimensional field of galaxy flow and density. “We really can’t claim to have a good understanding of cosmology if we cannot explain this motion,” says Tully.

This method is superior to merely mapping the location of matter, because it enables scientists to build a map of uncharted regions of the Universe, says Paulo Lopes, an astrophysicist at the Valongo Observatory, part of the Federal University of Rio de Janeiro. It relies on detecting the galaxies’ influence, rather than seeing them directly.

Moreover, the galaxies’ motions reflect the distribution of all matter, not just that which is visible in our telescopes — including dark matter.

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