Why are the giant supergalactic planes filled primarily with a single type of galaxy? This long-standing astronomical mystery may finally be solved.The Milky Way, our cosmic home, is located in a vast expanse of land known as the Local Galaxy Supercluster. This huge structure includes countless giant galaxy clusters and numerous individual galaxies. Superclusters are characterized by their pancake-like configuration and are nearly 1 billion light-years across, hence the name supergalactic plane.
Most galaxies in the universe fall into two categories: the first are elliptical galaxies, which are mainly composed of old stars and often contain extremely massive central black holes; the second are active star-forming disk galaxies with a spiral structure similar to the Milky Way. These two types of galaxies also exist in the local supercluster, but while the supergalactic plane is filled with bright elliptical galaxies, there is a noticeable lack of bright disk galaxies.
People have known about the existence of this strange separation of galaxies in our universe since the 1960s, and it is prominently featured in a list of "cosmic anomalies" recently compiled by Jim Peebles, a famous cosmologist and 2019 Nobel Prize winner.
Now, an international team led by University of Helsinki astrophysicists Till Sawala and Peter Johansson seems to have found an explanation. In an article published in Nature Astronomy, they show how the different distributions of elliptical and disk galaxies arise naturally due to different environments inside and outside the supergalactic plane.
"In dense galaxy clusters on the supergalactic plane, galaxies interact and merge frequently, forming elliptical galaxies and growing supermassive black holes. In contrast, galaxies far away from the supergalactic plane can evolve in relatively isolated environments, which helps them maintain their spiral structure," Tiel-Zavala said.
In their work, the team took advantage of the SIBELIUS (Simulation Beyond the Local Universe) simulation, which tracks the evolution of the universe from the early universe to the present 13.8 billion years ago. It runs on supercomputers in the UK and the CSCMahti supercomputer in Finland.
While most similar simulations consider random slices of the universe and cannot be compared directly with observations, the SIBELIUS simulations aim to accurately reproduce observed structures, including local superclusters. The final simulation results were surprisingly consistent with the observations.
"Last December, by chance, I was invited to attend a symposium in memory of Jim Peebles, where he introduced this problem. I realized that we had completed a simulation that might contain the answer," commented Till Sawala. "Our study shows that known mechanisms of galaxy evolution also operate in this unique cosmic environment."
Next to the Department of Physics, there is a large statue on the Kunpra campus of the University of Helsinki showing the distribution of galaxies in the Local Supercluster. The statue was inaugurated 20 years ago by British cosmologist Carlos Frenk, a co-author of the new study. "
"The distribution of galaxies in the local supercluster is indeed remarkable. But this is not an anomaly. Our results show that our standard model of dark matter is capable of producing the most remarkable structure in the universe," Frenck said of the new results.
Reference: "The different distribution of elliptical galaxies and disk galaxies in the local supercluster is a prediction of ΛCDM" co-authored by Till Sawala, Carlos Frenk, Jens Jasche, Peter H. Johansson and Guilhem Lavaux, November 20, 2023, "Nature - Astronomy".
DOI:10.1038/s41550-023-02130-6
Compiled source: ScitechDaily