An international science effort launched to identify dark matter throughout the universe has released its first results in the form of a map showing the concentrations of the mysterious substance across the cosmos.
An international collaboration, the Dark Energy Survey, has presented its initial findings on the invisible web of dark matter — detectable only by its gravitational influence on visible stars and galaxies — at a conference of the American Physical Society.
The first map, although showing just 0.4 percent of the visible sky, nevertheless shows areas of dark matter densities in unprecedented detail.
Such detail is necessary to tease out the existence of dark matter by detecting its subtle warping of the light coming to Earth from extremely distant galaxies.
"Our goal all this time has been to see the invisible — to see dark matter," said Sarah Bridle, an astrophysicist at the University of Manchester and one of the leaders of the survey group responsible for producing the map.
"To be able to look at a map and say, 'That part of the sky's got more dark matter in it, that bit's empty,' is the dream that we've had all this time," she said.
The map was created from photographs of galaxies in a swathe of Southern Hemisphere sky, using a 570 megapixel camera on a telescope at the Cerro Tololo Inter-American Observatory in Chile.
Identifying distortions in the shapes of galaxies located at great distances allowed the scientists to map the dark matter between those galaxies and the Earth.
"We measured the barely perceptible distortions in the shapes of about 2 million galaxies to construct these new maps," says Vinu Vikran, who led that analysis as a postdoctoral researcher at the University of Pennsylvania.
Dark matter is believed to be the main factor behind the creation of some of the universe's largest cosmic structures, a belief that was borne out by the first map.
"We identify some truly massive structures, about 100 million light years across," says Chihway Chang of the Swiss Federal Institute of Technology in Zurich, referring to areas of the map suggesting giant voids in dark matter in some regions and superclusters of it in other areas.
The survey has been dubbed the Dark Energy Survey, not Dark Matter, because its eventual goal is a map of dark matter of such detail as to allow scientists to estimate the strength of dark energy, a force as elusive and mysterious as dark matter, believed to be the reason the universe is expanding at an ever-accelerating rate.
