A map of dark matter has been released by the Dark Energy Survey, which was created using one of the world's most powerful digital cameras. Scientists say this is the first map of dark matter to be released in a series showing its spread across the cosmos.
These are the largest contiguous maps created at such great detail and are expected to improve our understanding of dark matter and its mysterious nature – answering questions about what role it plays in the formation of galaxies and how or if dark energy causes the expansion of the universe to speed up.
The maps were released at the meeting of the American Physical Society in Baltimore, Maryland.
What is dark matter?
Dark matter is the mysterious substance that makes up about 27% of the universe, according to a theoretical model of its composition.
Scientists are far surer of what dark matter is not than what it is. It is dark, so it cannot be seen – meaning it is not in the form of stars or planets we can see. Current observations show there is far too little visible matter in the universe to make up the 27% that is lacking.
We also know it is not made up of dark clouds of normal matter because we would be able to detect them through the absorption of radiation. It cannot be antimatter because we do not see unique gamma rays produced when antimatter interacts with matter.
Finally, scientists say it cannot be galaxy-sized black holes because of how many gravitational lenses we see.
Analysis of the "clumpiness" of dark matter will enable scientists to look at the nature of it. Dark matter is invisible to even the most sensitive astronomical instruments because it does not emit – or blocks out – light.
However, its effects can be seen through gravitational lensing, which occurs when the gravitational pull of dark matter bends light around far away galaxies.
Scientists were able to create the maps using the Dark Energy Camera – a 570-megapixel imaging device that is the primary instrument for the project.
The camera was created at the US Department of Energy's Fermi National Accelerator Laboratory. The new maps cover about 3% of the area of sky the project will document over its five year mission.
As the project progresses, scientists hope to test current theories about dark matter. One of these is that galaxies will tend to form where large concentrations of dark matter are because there is more dark matter in the universe than there is visible matter, hence stronger gravity.
Current data supports this idea, with the map showing large filaments of matter where galaxies and galaxy clusters lie, and cosmic voids where there are few galaxies.
Researcher Chihway Chang said: "Our analysis so far is in line with what the current picture of the universe predicts. Zooming into the maps, we have measured how dark matter envelops galaxies of different types and how together they evolve over cosmic time. We are eager to use the new data coming in to make much stricter tests of theoretical models."
Research leader Vinu Vikram, from the Argonne National Laboratory, said: "We measured the barely perceptible distortions in the shapes of about two million galaxies to construct these new maps. They are a testament not only to the sensitivity of the Dark Energy Camera, but also to the rigorous work by our lensing team to understand its sensitivity so well that we can get exacting results from it."