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Universal density profile for cosmic voids

Cosmic voids are fascinating for several reasons. For example, they were the first places in the Universe to be dominated by dark energy. They make up the majority of the volume of the Universe today and constitute an exceptional source of cosmological information. In contrast to the dense regions, where non-linear gravitational collapse has erased information about the primordial Universe, voids, in their more orderly outflow, hold memory of their initial states and hence about the physics of the beginning. Nico Hamaus, Paul Sutter and Benjamin Wandelt have carried out recent research works showing that a "simple" equation could describe large-scale bubbles.

Simulations containing more than eight billion dark matter particles demonstrated once again that dark matter clustered and created voids having a wide range of shapes and sizes. These simulations omitted ordinary matter, since there is so little of it compared to dark matter but included dark energy, which influences the continuous expansion of space. Previous studies undertaken by the three scientists demonstrated that the central regions of these voids have a universal formula for the density profile of dark matter. But the present study still goes further. The universal profile continues to a density maximum in the walls that separate voids, and then declines again as one enters the next void. Furthermore, this simple shape of density profile could be adapted to voids of all sizes and from different eras in cosmic history.

This universal formula for density profile of dark matter in voids could be used to study the nature of dark matter, neutrinos and perhaps even to test Einstein's theory of gravity. Yet until very recently voids were overlooked as sources of cosmological information, in contrast to bright and shiny galaxies. According to Benjamin Wandelt, co-author of this study, gleaning information from the near-empty parts of the universe is a bit like appreciating the silences in a piece of music...

To find out more:
"Better Not Avoid A Cosmic Void" (http://www.insidescience.org/content/better-not-avoid-cosmic-void/1751)
"Focus: Universal Formula for Cosmic Voids" (http://physics.aps.org/articles/v7/69)

Contact:

Nico Hamaus - TÚl. 33-1- 44 32 80 37 - hamaus at iap point fr

September 2014

Institut d'Astrophysique de Paris - 98 bis boulevard Arago - 75014 Paris