Most accurate measurement of elusive dark matter made

Washington: Scientists have made the most accurate measurement ever of the dark matter in the present- day universe, providing support to the theory that the elusive particle makes up majority of the cosmos.

The measurements of the amount and "clumpiness" (or distribution) of dark matter were made with a precision that, for the first time, rivals that of inferences from the early universe by the European Space Agency's orbiting Planck observatory.

The new results from the Dark Energy Survey (DES) collaboration is close to "forecasts" made from the Planck measurements of the distant past, allowing scientists to understand more about the ways the universe has evolved over 14 billion years.

"For the first time, we are able to see the current structure of the universe with the same clarity that we can see its infancy, and we can follow the threads from one to the other, confirming many predictions along the way," said Scott Dodelson from US Department of Energy's (DOE) Fermi National Accelerator Laboratory.

Most notably, the result supports the theory that 26 per cent of the universe is in the form of mysterious dark matter and that space is filled with an also-unseen dark energy, which is causing the accelerating expansion of the universe and makes up 70 per cent.

Paradoxically, it is easier to measure the large-scale clumpiness of the universe in the distant past than it is to measure it today.

In the first 400,000 years following the Big Bang, the universe was filled with a glowing gas, the light from which survives to this day.

Planck's map of this cosmic microwave background radiation gives us a snapshot of the universe at that very early time.

Since then, the gravity of dark matter has pulled mass together and made the universe clumpier over time. However, dark energy has been fighting back, pushing matter apart.

Using the Planck map as a start, cosmologists can calculate precisely how this battle plays out over 14 billion years.

"The DES measurements, when compared with the Planck map, support the simplest version of the dark matter/dark energy theory," said Joe Zuntz, of the University of Edinburgh in the UK.

"The moment we realised that our measurement matched the Planck result within seven per cent was thrilling for the entire collaboration," said Zuntz.

The primary instrument for DES is the 570-megapixel Dark Energy Camera, one of the most powerful in existence, able to capture digital images of light from galaxies eight billion light-years from Earth.

Scientists on DES are using the camera to map an eighth of the sky in unprecedented detail over five years.

The fifth year of observation will begin in August. The new results draw from data collected only during the survey's first year, which covers 1/30th of the sky.