Cosmic voids may contain 20pc of universe's 'normal' matter

Massive cosmic voids, regions of the space thought to be almost empty till now, may actually contain as much as 20 per cent of the 'normal' matter in the universe, a new study has found.
Researchers from the University of Innsbruck in Austria suggest that galaxies make up only 1/500th of the volume of the universe.
Recent measurements of cosmic microwave radiation using modern satellite observatories like The Cosmic Background Explorer (COBE), The Wilkinson Microwave Anisotropy Probe (WMAP) and Planck suggest that the composition of the universe consists of 4.9 per cent 'normal' matter, that makes up stars, planets, gas and dust, or 'baryons', whereas 26.8 per cent is the mysterious and unseen 'dark matter', and 68.3 per cent is the even more mysterious 'dark energy'.

Complementing these missions, ground-based observatories have mapped the positions of galaxies and, indirectly, their associated dark matter over large volumes, showing that they are located in filaments that make up a 'cosmic web', researchers said.
They investigated this in more detail, using data from the Illustris project, a large computer simulation of the evolution and formation of galaxies, to measure the mass and volume of these filaments and the galaxies within them.
Illustris simulates a cube of space in the universe, measuring some 350 million light years on each side. It starts when the universe is just 12 million years old, a small fraction of its current age, and tracks how gravity and the flow of matter changes the structure of the cosmos up to the present day.

The simulation deals with both normal and dark matter, with the most important effect being the gravitational pull of the dark matter.

When researchers looked at the data, they found that about 50 per cent of the total mass of the universe is in the places where galaxies reside, compressed into a volume of 0.2 per cent of the universe we see, and a further 44 per cent is in the enveloping filaments.
Just 6 per cent is located in the voids, which make up 80 per cent of the volume.
Researchers also found that a surprising fraction of normal matter - 20 per cent - is likely to be have been transported into the voids.

The culprit appears to be the supermassive black holes found in the centres of galaxies. Some of the matter falling towards the holes is converted into energy.
This energy is delivered to the surrounding gas, and leads to large outflows of matter, which stretch for hundreds of thousands of light years from the black holes, reaching far beyond the extent of their host galaxies.
"This simulation, one of the most sophisticated ever run, suggests that the black holes at the centre of every galaxy are helping to send matter into the loneliest places in the universe. What we want to do now is refine our model, and confirm these initial findings," said Markus Haider from University of Innsbruck.

The findings were published in the journal Royal Astronomical Society.