Hubble creates 3-D map of 'Dark Matter'

The Hubble Space Telescope has helped an international team of astronomers create a three-dimensional map of 'dark matter' that provides the first direct look at the large-scale distribution of dark matter in the universe.

Dark matter is an invisible form of matter that accounts for most of the universe's mass, and according to the researchers, the map provides the best evidence yet that normal matter, largely in the form of galaxies, accumulates along the densest concentrations of dark matter. According to the research team, the map, which stretches halfway back to the beginning of the universe, shows how dark matter has grown increasingly "clumpy" as it collapsed under gravity.

It also reveals a loose network of filaments that grew over time and intersected in massive structures at the locations of clusters of galaxies, the researchers said.

Richard Massey and Nick Scoville from the California Institute of Technology, who presented the findings at the 209th meeting of the American Astronomical Society in Seattle, Washington, said the 3-D map was a milestone, that would help astronomers take the study of dark matter in the universe from the level of "inference to direct observation".

Previous studies of dark matter were based largely on numerical simulations of the expected evolution of large-scale structure, whereas this study showed that evolution was driven by the gravitational attraction of dark matter, they said.

According to the two, the new maps of dark matter and galaxies will also provide critical observational underpinnings to future theories for how structure formed in the evolving universe under the relentless pull of gravity.

"It's reassuring how well our map confirms the standard theories for structure formation." said Massey.

"Dark matter is the 'scaffolding' inside of which stars and galaxies have been assembled over billions of years. Theories suggest the universe transitioned from a smooth distribution of matter into a sponge-like structure of long filaments. Mapping dark matter's distribution in space and time is fundamental to understanding how galaxies grew and clustered over billions of years," he said.

"Tracing the growth of clustering in the dark matter may eventually also shed light on dark energy, a repulsive form of gravity that influences how dark matter clumps," he added.

For creating the map, Hubble photographed 575 slightly overlapping views of the universe using the Advanced Camera for Surveys' (ACS) Wide Field Camera onboard the telescope.

The European Southern Observatory's Very Large Telescope in Chile, and the Subaru telescope in Hawaii obtained a further 1000 hours of observations of thousands of galaxies' spectra.

Finally, a study of the hot gas in the densest galaxy clusters was imaged in X-rays by the ESA's XMM-Newton telescope and the distances accurately determined through their spectral redshifts to arrive at the map.