Astrophysicists have found an answer to why spiral galaxies like our own Milky Way are largely missing from a part of our Local Universe called the Supergalactic Plane, an enormous, flattened structure extending nearly a billion light years across in which the Milky Way is embedded.
While the Plane is teeming with bright elliptical galaxies, bright disk galaxies with spiral arms are conspicuously scarce. Now an international team of researchers, co-led by Durham University, UK, and the University of Helsinki, Finland, say different distributions of elliptical and disk galaxies arise naturally due to the contrasting environments found inside and outside the Plane.
In the dense galaxy clusters found within the Supergalactic Plane, galaxies experience frequent interactions and mergers with other galaxies. This transforms spiral galaxies into elliptical galaxies – smooth galaxies with no apparent internal structure or spiral arms – and leads to the growth of supermassive black holes. By contrast, away from the Plane, galaxies evolve in relative isolation, which helps them preserve their spiral structure.
The research team used the SIBELIUS (Simulations Beyond the Local Universe) supercomputer simulation, which follows the evolution of the Universe over 13.8 billion years from the early Universe to the present day. While most cosmological simulations consider random patches of the Universe, SIBELIUS aims to precisely reproduce the observed structures, including the Supergalactic Plane. The final simulation is remarkably consistent with observations of our Universe through telescopes.
Research co-author Professor Carlos Frenk, Ogden Professor of Fundamental Physics, in the Institute for Computational Cosmology, Durham University, said: “The distribution of galaxies in the Supergalactic Plane is indeed remarkable.
“It is rare but not a complete anomaly: our simulation reveals the intimate details of the formation of galaxies such as the transformation of spirals into ellipticals through galaxy mergers.
“Further, the simulation shows that our standard model of the Universe, based on the idea that most of its mass is cold dark matter, can reproduce the most remarkable structures in the Universe, including the spectacular structure of which the Milky Way is part.”
The supercomputer simulations were performed on the Cosmology Machine (COSMA 8) supercomputer, hosted by the Institute for Computational Cosmology at Durham University on behalf of the UK’s DiRAC High-Performance Computing facility and on CSC’s Mahti supercomputer in Finland. The research was funded by the European Research Council, the Academy of Finland, and the UK Science and Technology Facilities Council.
hammer-comparison-large-black.jpg: Distribution of the brightest galaxies in the Local Universe, observed in the 2MASS survey (left panel) and reproduced in the SIBELIUS simulation (right panel). Both panels show projections in supergalactic coordinates, out to approximately 100 Megaparsec (Mpc). The nearly vertical empty stripe represents the region of the sky hidden behind our own Milky Way galaxy. The simulation accurately reproduces the structures seen in the Local Universe. Credit Dr Till Sawla (University of Helsinki).
“Distinct distributions of elliptical and disk galaxies across the Local Supercluster as a ΛCDM prediction”, Sawala, T, Frenk, C.S. et al, is published in Nature Astronomy. DOI: 10.1038/s41550-023-02130-6