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Orbits of galaxies in the Local Supercluster. Credit: Brent Tully.

A team of astronomers from Maryland, Hawaiʻi, Israel and France has produced the most detailed map ever of the orbits of galaxies in our extended local neighborhood, showing the past motions of almost 1,400 galaxies within 100 million light years of the Milky Way.

The team, including co-author Brent Tully of the Institute for Astronomy at the University of Hawaiʻi, reconstructed the galaxies’ motions from 13 billion years in the past to the present day. The main gravitational attractor in the mapped area is the Virgo Cluster, with 600 trillion times the mass of the Sun, 50 million light years from us.

More than a thousand galaxies have already fallen into the Virgo Cluster, while in the future all galaxies that are currently within 40 million light years of the cluster will be captured. The Milky Way galaxy lies just outside this capture zone. However, the Milky Way and Andromeda galaxies, each with 2 trillion times the mass of the Sun, are destined to collide and merge in five billion years.

“For the first time, we are not only visualizing the detailed structure of our Local Supercluster of galaxies but we are seeing how the structure developed over the history of the universe,” said Tully. “An analogy is the study of the current geography of the Earth from the movement of plate tectonics.”

Pieces of a larger picture

These dramatic merger events are only part of a larger show. There are two overarching flow patterns within this volume of the universe. All galaxies in one hemisphere of the region—including the Milky Way—are streaming toward a single flat sheet. In addition, essentially every galaxy over the whole volume is flowing, as a leaf would in a river, toward gravitational attractors at far greater distances.

Representations of the orbits can be seen in a video and, alternatively, with an interactive model. With the interactive model, a viewer can pan, zoom, rotate and pause/activate the time evolution of movement along orbits. The orbits are shown in a reference frame that removes the overall expansion of the universe. Viewers are shown the deviations from cosmic expansion caused by the interactions of local sources of gravity.

The study, “Action Dynamics of the Local Supercluster,” was published in the The Astrophysical Journal.

Lead author Ed Shaya of the University of Maryland conducted this research in collaboration with Tully, Yehuda Hoffman of Hebrew University in Israel, and Daniel Pomarede of the University of Paris-Saclay in France.

—By Roy Gal

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