Jerusalem scientists help shed light on large-scale cosmic structures

Where does the Milky Way reside? We live there and know it got its name from a Greek myth about the goddess Hera who sprayed milk across the sky.

Thunder god Zeus placed his son – the infant Heracles, born to a mortal woman, on Hera’s breast while she was asleep so the baby would drink her milk and become immortal. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby; she pushes the baby away, some of her milk spills, and it produces the band of light known as the Milky Way, according to mythology.

But until now, we have not known where it is, given the fact that it’s just a single galaxy among billions in the universe.

Looking back at how astronomy developed its theories over time, one can understand how astronomers and philosophers wrestled with understanding the nature of galaxies and the vastness of our universe.

The Milky Way is the galaxy that includes our solar system, with the name describing the galaxy’s appearance from Earth – a misty band of light seen in the night sky formed from stars that cannot be individually distinguished without a powerful telescope.

The Milky Way is a barred spiral galaxy only about 1,000 light-years thick at the spiral arms and more at the bulge). Recent simulations suggest that a dark matter area, also containing some visible stars, may extend up to a diameter of almost 2 million light-years. The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster, which is itself a component of the Laniakea Supercluster.

Astrophysicists believe it includes 100 billion to 400 billion stars and at least that number of planets.

A history of discovery

Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the universe, but they were way off.

In 1929, American astronomer Edwin Hubble used the largest telescope of his time to supply the first observational evidence for the universe having a finite age and discovered that the more distant a galaxy is from Earth, the faster it appears to be receding into space, meaning that the universe is expanding uniformly in all directions) that the Milky Way is just one of many galaxies.

Hubble was thanked by Albert Einstein for contributing to his theories. Hubble’s name has since been honored for a powerful space telescope.

NOW, AN international study that included scientists from the Hebrew University of Jerusalem has mapped out the gravitational “basins of attraction” in the local universe, offering fresh insights into the large-scale cosmic structures that shape the movement of galaxies.

They have just published their findings in the prestigious journal Nature Astronomy under the title “Identification of basins of attraction in the local universe.”

Using advanced data from the Cosmicflows-4 compilation of distances and velocities of roughly 56,000 galaxies, the team applied cutting-edge algorithms to identify regions where gravity dominates, such as the Sloan Great Wall and the Shapley Supercluster. This research suggests that our Milky Way most probably resides within the larger Shapley basin, shifting our understanding of cosmic flows and the role of massive structures in shaping the universe’s evolution.

The team members said they had taken a significant step forward in understanding the vast structure of the universe, identifying key gravitational regions known as “basins of attraction.” They maintained that it was important because it deepens our understanding of the large-scale structure of the universe and the gravitational forces that shape it.

By mapping out the basins of attraction – regions where gravity pulls galaxies and matter, they continued, the study reveals how massive cosmic structures influence the movement and formation of galaxies over time.

“Understanding these dynamics not only helps us better grasp the universe’s past and its ongoing evolution but also provides valuable insights into fundamental cosmological questions, such as the distribution of dark matter and the forces driving cosmic expansion. This knowledge has the potential to refine our models of the Universe and guide future astronomical research.”

The research, led by Dr. A. Valade at Potsdam’s Liebnitz Institute for Astrophysics during his doctoral work under the supervision of Prof. Yehuda Hoffman from the Hebrew University and Prof. Noam Libeskind from Potsdam, also involved contributions from scholars at the University of Paris-Saclay and the University of Hawaii.

The study is based on the widely accepted Lambda Cold Dark Matter standard model of cosmology, which suggests that the universe’s large-scale structure emerged from quantum fluctuations during the early stages of cosmic inflation. These minute fluctuations in density evolved, forming the galaxies and clusters we observe today. As these density perturbations grew, they attracted surrounding matter, creating regions where gravitational potential minima, or basins of attraction, formed.

Earlier catalogs had suggested that the Milky Way Galaxy was part of a region called the Laniakea Supercluster, but the new CF4 data offer a slightly different perspective, indicating that Laniakea might be part of the much larger Shapley basin of attraction that includes an even greater volume of the local universe.

Among the newly identified regions, the Sloan Great Wall stands out as the largest basin of attraction, with a volume of about half a billion cubic light-years, more than twice the size of the Shapley basin, which was previously considered the largest. These findings provide an unprecedented look into the gravitational landscape of the local universe, offering new insights into how galaxies and cosmic structures evolve and interact over time.