A recent study by researchers at the University of Pennsylvania may shed light on the distribution of one of the most mysterious substances in the universe: dark matter.
In the 1970s, scientists noticed something strange about the movements of galaxies. The observations of the curves of revolution of the stars around the center of their galaxy show that they turn too quickly if one bases oneself on the law of gravitation of Newton or on the mass deduced from the luminosity of the galaxies. Most likely there is hidden non-luminous matter, dark matter, which surrounds, still shapes the stars within each galaxy. Galaxies which would themselves be surrounded by a halo of dark matter. Recent work by researchers Bhuvnesh Jain and Eric Baxter, professors of physics at the Pennsylvania School of Arts and Sciences, may give us new insights into the structure of these mysterious halos.
Think of a dark matter halo as a hypothetical component of a galaxy that envelops the galactic disk and extends far beyond the galaxy’s visible boundaries. The mass of the halo is the dominant portion of the total mass of the galaxy. Because they are made of dark matter, halos cannot be observed directly, but their existence is inferred from their effects on the motion of stars and gas in galaxies. In this study, the researchers investigated the structural features of halos in different clusters of galaxies. The goal was to find out if these dark matter halos had clearly defined boundaries.
Researchers have generally imagined a fairly smooth transition of matter between each galaxy, but for Bhuvnesh Jain and Eric Baxter, computer simulations should show that there is a sharp, distinct transition that we should be able to see through a careful data analysis. Thus, after analyzing data collected by the Sloan Digital Sky Survey, in New Mexico, on thousands of galaxy clusters, the researchers noticed that there was indeed a concentration of matter on the edges of the halos, while a sharp drop in the density distribution of galaxies was observed beyond its borders.
» You have this big halo of dark matter”explains one of the researchers, “this halo has accreted matter throughout its history. When this material is attracted to the halo, it begins to pick up speed. She gets faster and faster and when she finally falls into the halo, she then starts « splattering » all over the place before slowing down. Because this effect occurs in all directions, it leads to an accumulation of material at the edges of the halo and we therefore observe a sharp drop in the density of material just behind this limit”.
Thus, the edges of these dark matter halos would be well delimited and not smoothed as previously suggested. Astronomers now hope their research will contribute to a better understanding of this mysterious substance thought to make up around 80% of the matter in the universe.