An article published in the journal “Nature Astronomy” describes the creation of a map of the network of filaments that connects matter all around the universe. A team of researchers analyzed the data collected during previous surveys to find the gravitational effects that reveal the shapes of those filaments. Those small gravitational distortions suggest that they’re hundreds of millions of light years long and that they’re made of dark matter.
The cosmic web is a large-scale structure of the matter of the universe that includes dark matter, still a theoretical concept because its existence hasn’t been proven yet and there are alternative models that don’t include its existence. However, the filaments that make up that cosmic web could be composed of dark matter so their study is a testing ground for the various existing models.
Dark matter isn’t studied directly but through its gravitational effects, and this is also true for the filaments in this study. Shirley Ho from Berkeley Lab and Carnegie Mellon University, who directed this study, compared her team’s search for filaments to Google and Yahoo in image recognition when those services recognize street names on road signs or find cats in photos.
Among the data used there are those of the Baryon Oscillation Spectroscopic Survey (BOSS), which involved about 1.5 million galaxies studied to obtain information on universe expansion and matter distribution. Among the results there’s a catalog of the probable filament structures that connect clusters of matter that was used by the researchers for their study.
Other measurements used come from the cosmic microwave background (CMB) radiation. The researchers focused on its anisotropies, which means the regular fluctuations that were mapped in previous surveys. Sophisticated algorithms were used to look for filament marks in gravitational distortions caused by what’s called gravitational lensing, in this case weak.
The image below (courtesy Siyu He, Shadab Alam, Wei Chen, and Planck/ESA, All Rights Reserved) shows the trajectory of the cosmic microwave background radiation modified by the filaments’ force of gravity. Those electromagnetic emissions were captured by ESA’s Planck Surveyor satellite to create a global map presented in March 2013. The data collected are available for various types of research including this one on filaments.
The map of the filaments created by putting together all the data and applying various models and theories shows its evolution over time. The image above (courtesy of Yen-Chi Chen and Shirley Ho. All Rights Reserved) shows two moments: on the left the web 12.3 billion years ago and on the right 7.4 billion years ago.
This map can help cosmological research of various kinds in addition to those specifically concerning filaments. It will help some tests of the theory of relativity, research on dark matter and possible alternative models and maybe also provide clues about the nature of dark energy, another concept that for the moment is purely theoretical.