For decades, scientists have observed signs of a threadlike structure connecting galaxies across the universe. Theories, computer models, and indirect observations have shown that there is a network of dark matter in the universe that connects galaxies and establishes the large-scale structure of the universe. But if the fibers that make up this network are dense, dark matter is extremely difficult to observe.
Today, researchers published the first composite image of a dark matter filament connecting galaxies together.
Filaments of dark matter connect the space between galaxies in this false-color image. The locations of bright galaxies are shown in white areas and the presence of dark matter filaments connecting the galaxies is shown in red. Photo: S. Epps/M. Hudson/University of Waterloo.
Dark matter, an elusive type of matter estimated to make up 17% of the universe, does not radiate, reflect or absorb light. This makes dark matter virtually undetectable, except for its effects when it exerts a gravitational pull or when it bends the light of distant galaxies, what we call the osmotic effect.
For their work, Hudson and co-author Seth Epps, who was a master’s student at the University of Waterloo at the time of the study, used a technique called “weak gravitational lensing” – a statistical measure of slight curvature which occurs in the path of light entering near where the mass is located. Gravitational lensing makes images of galaxies appear slightly curved due to the presence of mass, such as that of dark matter.
In the paper, they explain that to study the weak lensing signal from dark matter filaments, they needed two sets of data: a catalog of pairs of galaxy clusters affected by the effect and a catalog of galaxies of background with precise distance measurements.
They combined lensing data from a multi-year survey of the sky at the Canada-France-Hawaii Telescope with SDSS data on Bright Red Galaxies (LRGs), which are massive, distant, and very old galaxies.
“LRGs are very bright galaxies. They tend to be more massive than average galaxies and “live” in heavier dark matter “halos.” It is reasonable to expect that the fibers or bridges between them will also be heavier than normal,” Hudson told Seeker via email.
Hudson and Epps combined more than 23,000 pairs of galaxies, all located about 4.5 million light years apart. This allowed them to create a composite image showing the presence of dark matter between galaxies. Hudson told Seeker that the filament in their “image” is the average of 23,000 pairs of galaxies.
“The main reason we used these galaxies is that they have precise distances (as measured by another research group),” says Hudson. “These distance measurements allow us to distinguish true 3D “galactic pairs” (i.e. they are both at the same distance from us), galaxies close together in the sky but in reality at distances very different distances.
The pairs of 3D galaxies will be physically close to each other and therefore will have a bridge, while the other group (unpaired galaxies) will not, so there will be no bridge between these galaxies. Hudson and Epps say their results show that the bridge of dark matter filaments is strongest between systems less than 40 million light years apart.
“Using this technique, we will not only be able to see that these dark matter filaments exist in the universe, but we will also be able to see the extent to which these filaments connect celestial objects together,” Epps said in a statement. statement.
The Big Bang theory predicts that fluctuations in the density of matter during the early moments of the universe caused large amounts of matter to accumulate in the universe in a network of tangled filaments. To explain this, astronomer Fritz Zwicky first introduced the concept of dark matter in 1933, when his measurements of galaxies moving within galaxy clusters showed that they must be abundant, at least ten times more invisible matter than what is present.
But this was not recognized until the 1970s, when dark matter began to be seriously considered. Vera Rubin and Kent Ford Jr. mapped the motions of stars in galaxies near our own Milky Way, and they also concluded that each galaxy must be made up of large amounts of invisible matter, far more than all the visible matter. Later, computer simulations confirmed this and suggested the presence of dark matter, structured like a network, with long filaments connected to each other at the locations of large galaxy clusters.
In their paper, Hudson and Epps list dozens of previous studies that have attempted to measure and observe dark matter networks, and they say they hope that their techniques for superimposing filaments between groups and clusters of galaxies could become the basis future studies on dark matter filaments. They hope that further studies and telescopes will continue to expand our understanding of dark matter.
Source: Researcher, Space