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UH Astronomer Maps Massive Void Bordering Milky Way

July 27, 2019, 9:00 AM HST (Updated July 24, 2019, 3:37 AM)
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A smoothed rendition of the structure surrounding the Local Void. Our Milky Way galaxy lies at the origin of the red-green-blue orientation arrows (each 200 million light years in length). We are at a boundary between a large, low density void and the high density Virgo cluster. University of Hawaiʻi courtesy image.

A new study published by an astronomer at University of Hawaiʻi’s Institute for Astronomy (IfA) and an international team of researchers reveals a massive cosmic structure surrounding our Milky Way galaxy.

Brent Tully of IfA and his team mapped the size and shape of a vast empty region of space known as the “Local Void” which borders our cosmic neighborhood. The team deduced the void’s structure by observing the movement of surrounding galaxies and generating a three-dimensional map that recreates their motion.

The map reveals how galaxies are influenced by the expanding force of the universe, as well as the gravitational pull of neighboring galaxies and regions of dense mass. Overall, they move towards higher concentrations of mass and away from areas with voids.

The idea of a Local Void was first proposed by Tully and Richard Fisher in 1987. The theory is now widely accepted but has not been heavily researched due to its obscurity. But Tully and his team’s measurements of some 18,000 galaxies have now enabled the construction of a cosmographic map that shows the boundary between cosmic matter and the emptiness that defines the edges of the Local Void. In 2014, they used the same technique to identify the size and shape of the galactic supercluster of 100,000 galaxies we inhabit called Laniakea—or “immense heaven” in Hawaiian.

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Astronomers have been trying to identify why the motions of the Milky Way, our nearest large galaxy neighbor Andromeda, and their smaller neighbors deviate from the overall expansion of the universe for more than three decades. Tully’s study shows that half of this motion is caused by the combination of the gravitational pull of the neighboring Virgo Cluster and the expansion of the Local Void.

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