University of Maryland: Expanding Universe of Knowledge

Everything in our universe is constantly on the move, but on timescales so vast that the motion is not observable across human lifespans. In a new study, astronomers from the University of Maryland, the University of Hawai’i and the University of Paris-Saclay used a mathematical technique called “numerical action” to trace the movement of 10,000 galaxies and clusters of galaxies over 11.5 billion years—from their origins when the universe was 1.5 billion years old until today.

The research team’s study, which follows major groupings of matter within 350 million light-years of the Earth, was accepted for publication in The Astrophysical Journal. Using the same method, the team also projected future galaxy movements, predicting galaxy expansions and mergers 10 billion years into the future.

“We are bringing into focus the detailed formation history of large-scale mass structures in the universe by reverse-engineering the gravitational interactions that created them,” said Ed Shaya, the study’s lead author and an associate research scientist in UMD’s Department of Astronomy who helped numerical action.

The method allows researchers to compute the paths based on galaxies’ current brightness, position and motion. They factored in the physics of the Big Bang theory, including the idea that galaxies initially start out expanding from each other almost precisely at what’s known as the Hubble expansion rate, which stipulates that the farther from Earth galaxies are located, the faster they are moving away.

Over time, gravity alters galaxy motions, so they are not just moving apart as the universe expands, but are drawn together into filaments, walls and clusters, even as other regions are swept clean by gravity and become enormous voids. In regions of high density, however, the galaxy orbits can become quite complicated and involve collisions and mergers.

The researchers explored a vast regions of high matter and galaxy density called “the Great Attractor,” located the core of the Laniakea Supercluster, which contains our our own Milky Way. Galaxies can be seen flowing toward a location within a nest of four rich clusters.

“For more than 30 years, astronomers have considered a ‘Great Attractor’ to be the primary source of gravity that makes our home Milky Way Galaxy move with a high peculiar velocity relative to uniform cosmic expansion, but the nature of that source has been obscure,” said co-author R. Brent Tully Ph.D. ;72, an astronomer at the University of Hawai’i Institute for Astronomy “Our orbit reconstructions have provided the first good look at this previously enigmatic region.”

Using the same technique, the researchers found that the accelerating expansion of the universe will dominate the coming 10 billion years, causing most galaxies to move apart. However, some coalescence and merging will continue in localized regions.