An article published in the journal “Monthly Notices of the Royal Astronomical Society” reports the results of a study that indicates that the Milky Way is abnormally massive in relation to the so-called Local Sheet, the group of galaxies that surround it. A team of researchers used simulations conducted within the IllustrisTNG project and discovered that a galaxy in the same situation as the Milky Way should be much smaller than the cosmic wall that surrounds it. The simulations indicate that there’s one exception for every million galaxies in IllustrisTNG under the same conditions. This must be kept in mind in studies of galactic environments.
Groups of galaxies can form a so-called cosmic wall in which a very flat belt of galaxies surrounds other galaxies and has cosmic voids on its sides, regions where the density is extremely low. The Local Sheet is one of these walls and affects the rotation around its axis of the Milky Way and nearby galaxies, which would be less organized if they were in an area of space without a wall.
The IllustrisTNG project is generating accurate cosmic simulations, in this case, of an area almost a billion light-years across containing millions of galaxies. Only one in a million galaxies within a cosmic wall were found to be as massive as the Milky Way while nearly all were much smaller. The image (Miguel A. Aragon-Calvo. Simulation data: Illustris TNG project. CC BY 4.0) shows an image of the Milky Way superimposed on that of galaxies (represented as yellow dots) simulated in the IllustrisTNG project immersed in dark matter (in green and blue).
This result is interesting to understand which conditions can lead to exceptions such as the Milky Way and also shows how it is necessary to avoid taking certain results for granted in astronomical studies. The Milky Way is in many ways a very common galaxy, as spiral galaxies are the most numerous in the universe. That contributed to the idea that it constitutes a kind of cosmic normality. This study shows that things are different.
The researchers explained that not taking into full consideration the effects of our cosmic environment can lead to a Copernican bias. Copernicus’ studies led to the elimination of the idea that the Earth was at the center of the universe but that doesn’t mean it’s a place like any other. This must be kept in mind in the studies of the formation and evolution of the Milky Way and the surrounding area of the Local Sheet and perhaps even beyond.
