Astronomers have released a map showing dark matter and galaxies billions of light years across.

The vast cosmic map is a project of astronomers from the University of British Columbia and University of Edinburgh. The project took five years to complete and represents the images of more than 10 million galaxies. The monumental map is a big step forward in understanding dark matter, the mysterious substance that accounts for more than 83 percent of the mass in the cosmos.

Dark matter is an invisible substance that comprises majority of the mass in the universe. Scientists, still remain "in the dark" about dark matter because it can't be observed. Dark matter is not in the form of dark clouds of normal matter made up of particles called baryons. Dark matter is not antimatter because it doesn't radiate the unique gamma rays that are produced when antimatter interacts with matter. The most common view is that dark matter is made up of exotic particles like axions or weakly interacting massive particles.

So how did astronomers map a substance that can't be observed directly? The team of astronomers observed the gravitational effects of dark matter on ancient light travelling from distant galaxies. The team analyzed light from 10 million galaxies in four different regions of the sky.

"Light coming toward us from a distant galaxy is bent by the gravity of a lump of matter in the middle," explained Catherine Heymans of the University of Edinburgh.

"Einstein's theory of general relativity tells us that mass bends space and time, so when light comes toward us through the Universe, if it passes some dark matter, its light gets bent and the image we see gets bent and distorted. Dark matter is leaving its signature on the images of very distant galaxies."

Astronomers used a 340 megapixel camera called "MegaCam" attached to the Canada-France-Hawaii Telescope in Hawaii to capture images of ancient galactic light. The survey is about 100 times bigger than the previous map of dark matter collected by the Hubble telescope's Cosmic Evolution Survey or Cosmos. The map shows vast clusters of dark matter around galaxies.

"By analyzing light from the distant Universe, we can learn about what it has traveled through on its journey to reach us. We hope that by mapping more dark matter than has been studied before, we are a step closer to understanding this material and its relationship with the galaxies in our Universe," Heymans said.

The research was presented at the 219th meeting of the American Astronomical Society in Austin, Texas, on Monday.