An article published in the journal “Nature Astronomy” provides an explanation for the scarcity of spiral galaxies in the so-called Supergalactic Plane. A team of researchers used results obtained from the SIBELIUS supercomputer simulation to offer an explanation based on galaxy mergers. The analysis of the results indicates that in galaxy clusters present on the Supergalactic Plane, interactions and mergers are common with the result that spiral galaxies merge to become elliptical galaxies. Far from the Supergalactic Plane, galaxies are more isolated and therefore less likely to merge.
The image (NASA, ESA, CSA, Rogier Windhorst (ASU), William Keel (University of Alabama), Stuart Wyithe (University of Melbourne), JWST PEARLS Team, Alyssa Pagan (STScI)) shows an elliptical galaxy on the left and a spiral galaxy on the right.
The Supergalactic Plane is a colossal flattened cosmic structure composed of several galaxy superclusters, including Laniakea, the one which includes the Milky Way. There are a few hundred thousand galaxies in this structure that span almost a billion light-years.
Already in the 1960s, astronomers realized that the Supergalactic Plane contains mainly elliptical galaxies and very few spiral galaxies, the Milky Way’s class. This distribution is anomalous compared to that of other galaxy clusters in other areas of the universe. Jim Peebles, 2019 Nobel Prize winner for physics, spoke about this anomaly, calling it one of the five key questions of the universe at a conference held at the University of Durham. Also participating was Till Sawala of the University of Helsinki, lead author of a study that offers an answer to this question.
Till Sawala’s idea comes from the SIBELIUS (Simulations Beyond the Local Universe) project, which aims to recreate galaxies and structures in the observed universe by simulating their formation and evolution. The simulations were conducted using the Cosmology Machine (COSMA 8) supercomputer at the University of Durham.
Till Sawala and his collaborators examined simulation results, which show that galaxy interactions and mergers occur often in the Supergalactic Plane. A merger involving a spiral galaxy can radically change its structure, transforming it into an elliptical galaxy. Many mergers lead to a situation like the one observed in the Supergalactic Plane. Galaxies in other clusters outside the Supergalactic Plane that are less dense are more isolated and therefore less subject to mergers, with the consequence that a greater number of spiral galaxies can survive.
The SIBELIUS project’s simulations are based among other things on the idea that most of the mass of the universe consists of dark matter as described by the Lambda-CDM model. The match between the simulations and the observed structures also represents a confirmation for this model.
A galaxy merger takes many millions of years for the new galaxy to reach an equilibrium state. This means that astronomers can see examples of mergers in various stages but it’s impossible to follow this process. Increasingly sophisticated simulations such as the one created by the SIBELIUS project help to reconstruct these processes and test cosmological models.
