Those cosmic voids full of information

Simulation of the large-scale structure of the universe (Image Nico Hamaus, Universitäts-Sternwarte München, courtesy of The Ohio State University)
Simulation of the large-scale structure of the universe (Image Nico Hamaus, Universitäts-Sternwarte München, courtesy of The Ohio State University)

An article accepted for publication in the journal “Physical Review Letters” describes a research on the distribution of matter in the universe made in a way different from usual. An international team of researchers studied cosmic voids as if they were photographic negatives from which they could get information about ordinary matter, dark energy and dark matter.

Cosmic voids are empty areas of space where matter is almost entirely absent, in the order of an atom per cubic meter. Some particularly large voids are called supervoids and can be many tens of millions of light years across. These voids separate the large filaments of galaxies that started forming in the young universe when its temperature dropped enough to allow the formation of atoms and the density perturbations due to the force of gravity started coalescing them.

Our instruments can observe a part of the ordinary matter that forms galaxies, which is also used to track the expansion of cosmic voids with measures that are also used to test general relativity. In this research, the attention was focused on these voids, an approach that Paul Sutter, co-author of the article, a researcher at Ohio State University and associated INAF – Astronomical Observatory of Trieste, Italy, compared it to searching for information about Swiss cheese by studying its holes.

Any phenomena that contradict general relativity could generate effects too small compared to the great activities going on in galaxies so it can be easier to find them in cosmic voids. In this case, Paul Sutter compared the research to the identification of a firefly in a dark cornfield or in a lit-up city full of night life.

Paul Sutter also explained that in cosmic voids ordinary matter is almost absent but there’s a lot of dark energy. That’s the force that is causing the acceleration of the universe’s expansion. It’s still mysterious because we see its effects, contrary to those we expect given that the expansion was was thought to be slowing down due to the force of gravity, but basically we know nothing about its nature.

To investigate cosmic voids, the researchers performed computer simulations and compared them with part of data taken from the Digital Sky Survey, a survey that has created the best three dimensional maps of the universe ever made. The precision obtained from the simulations showed a four-times improvement in the models of accuracy of matter density and growth of cosmological structure from previous studies.

The scientists looked for small deviations in the behavior of the voids that might conflict with the theory of relativity but found none. The analyzes and models have been put online on a website created for the occasion to allow anyone interested to examine them and use them for future research. This interesting approach to research that from a point of view is in some ways opposite to normal could spur more useful studies.

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