Black holes blast matter into cosmic voids

The 'empty' voids between filaments of dark matter and galaxies could be hiding as much as 20 per cent of the normal matter in the cosmos, according to a new study.

Left: a section of the Illustris simulation showing the distribution of dark matter, with a width and height of 350 million lightyears and a thickness of 300,000 light years. Galaxies are found in the small, white, high-density dots.
Right: The same data showing the distribution of normal matter.
Credit: Markus Haider / Illustris collaboration

The Universe as we know it consists largely of unseen matter that also contains galaxies and other cosmic material. This is condensed into filaments that make up the cosmic web structure of the Universe, stretched around enormous voids in space that are thought to be largely empty.

Modern space-based observatories have enabled astronomers to define the various components that make up the Universe. Recent measurements show it consists of 4.9% normal matter – stars, dust, galaxies etc. – 26.8% dark matter and 68.3% dark energy.

Ground-based observatories have facilitated the mapping of galaxies in the Universe and, consequently, their associated dark matter. Through these observations, the structure of the Universe has been found to be web-like and has become known as the ‘cosmic web’.

Dr Markus Haider of the Institute of Astro- and Particle Physics at the University of Innsbruck has led a team that used data from a project called Illustris to measure the mass and volume of these web filaments and the galaxies within them.

Illustris measures out a ‘cube’ area in the Universe 350 million lightyears on each side, beginning when the Universe was 12 million years old and analysing how gravity and the flow of matter affects its structure over time.

The team found that about 50 per cent of the total mass of the Universe is contained where galaxies are found, compressed into a volume of 0.2 per cent of the Universe we see, while a further 44 per cent is contained in elsewhere in the filaments of the web-like structure. 6 per cent is located in the voids, despite the fact that these voids make up 80% of the volume of the cosmos.

But the astronomers also found that 20 per cent of normal matter is likely to have been blasted into the voids by the supermassive black holes at the centres of galaxies.

As supermassive black holes suck in matter, they convert some of it to energy, which heats surrounding gas and causes large jets of outflowing material that stretch for hundreds of thousands of lightyears. These jets are thought to blast the normal matter far beyond the galaxies in which they reside and into the cosmic voids.

If accurate, the simulations conducted by the team would explain why astronomers do not see the amount of normal matter in the Universe predicted by models. It would also mean that more normal matter resides in the voids between the filaments than previously thought.

"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,” says Dr Haider. “What we want to do now is refine our model, and confirm these initial findings."


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