Physicists have finally figured out why spiral galaxies like our own Milky Way are so scarce in a region of the cosmos known as the Supergalactic Plane.
The Supergalactic Plane is an enormous, flattened structure that stretches nearly a billion light-years across and contains our Milky Way galaxy. Although the Plane is teeming with luminous elliptical galaxies, spiral galaxies with distinctive spiral arms are noticeably absent.
Now, an international team of researchers led by Durham University in the UK and the University of Helsinki in Finland has discovered that the different distributions of elliptical and spiral galaxies are caused by the contrasting environments found within and outside the Plane.
Within the Supergalactic Plane, galaxies frequently interact and merge with other galaxies. These interactions transform spiral galaxies into elliptical galaxies, characterized by a smooth appearance with no obvious internal structure or spiral arms. These mergers also lead to the growth of supermassive black holes.
In contrast, galaxies outside the Plane can evolve in relative isolation. This isolation helps them maintain their spiral structure.
The findings were published in the journal Nature Astronomy.
The Milky Way is located within the Supergalactic Plane, which contains several massive galaxy clusters and thousands of individual galaxies. The vast majority of galaxies in this region are elliptical galaxies.
The research team used the SIBELIUS (simulations beyond the local universe) supercomputer simulation, which tracks the evolution of the universe from its early stages to the present day over 13.8 billion years.
Unlike most cosmological simulations, which consider random patches of the universe that cannot be directly compared to observations, SIBELIUS aims to precisely replicate observed structures, including the Supergalactic Plane. The final simulation is remarkably consistent with telescopic observations of our universe.
Professor Carlos Frenk, Ogden Professor of Fundamental Physics in the Institute for Computational Cosmology at Durham University, and co-author of the study, said, "The distribution of galaxies in the Supergalactic Plane is indeed remarkable. It is rare but not a complete anomaly. Our simulation reveals the intricate details of galaxy formation, such as the transformation of spirals into ellipticals through galaxy mergers. Furthermore, the simulation demonstrates that our current model of the universe, based on the idea that most of its mass is cold dark matter, can replicate the most remarkable structures in the universe, including the spectacular structure of which the Milky Way is a part."
A recent list of "cosmic anomalies" compiled by renowned cosmologist and 2019 Nobel laureate Professor Jim Peebles prominently features the peculiar separation of spiral and elliptical galaxies in the local universe.
Dr. Till Sawala, a postdoctoral researcher at Durham University and the University of Helsinki and the lead author of the study, said, "By chance, I was invited to a symposium in honor of Jim Peebles last December at Durham, where he presented the problem in his lecture. I realized that we had already completed a simulation that might contain the answer. Our research shows that the known mechanisms of galaxy evolution also work in this unique cosmic environment."
The Cosmology Machine (COSMA 8) supercomputer at Durham University's Institute for Computational Cosmology, hosted on behalf of the UK's DiRAC High-Performance Computing facility, and CSC's Mahti supercomputer in Finland were used to run the supercomputer simulations.