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Galaxies Form Inside of Dark Matter 'Clumps,' New Study Shows

The project allowed researchers to understand the relationship between dark matter and the galaxies better.
July 9, 2015, 2:18pm
A group of galaxies mapped by KiDS is shown on the left. On the right, is the same area of sky, but with invisible dark matter rendered in pink. Source: Kilo-Degree Survey Collaboration/A. Tudorica & C. Heymans/ESO

Scientists have been trying to suss out what dark matter—a hypothetical matter that physicists say makes up a large chunk of our universe—is for decades. And now, a team of international researchers say that the results from a new survey might bring us one step closer to explaining its role in our galaxies.

In a project dubbed the Kilo-Degree Survey (KiDS), researchers have been collecting data from the night sky using imaging from the VLT Survey Telescope and its huge camera, the OmegaCAM—located on ESO's Paranal Observatory in Chile.

"The goal of the survey is to map the dark matter distribution in the universe and to understand how the universe evolved, and what the properties of the galaxies that we observe in the universe are," Massimo Viola, a researcher from Leiden Observatory in the Netherlands, told me.

Viola explained that the first results were taken from only 7 percent of the final survey area. By studying gravitational lensing—when mass bends light—the researchers can map out the locations where gravity is strongest, and use this to work out where both matter and dark matter is found. The group analysed images of over two million galaxies, roughly 5.5 billion light-years away, using this approach.

"There are not that many ways of figuring out what dark matter is. Studying gravitational lensing is one way to map it because we look at this tapestry of distant galaxies far away in the universe, and how the light from those galaxies is being distorted on the way down to Earth," Lars Lindberg Christensen, the head of ESO ePod, told me.

The project, said Lindberg, allowed the researchers to understan the relationship between dark matter and the galaxies better.

The VLT Survey Telescope. Credit: ESO/G. Lombardi

"One of the main questions about galaxy formation in astrophysics is to understand how luminous the galaxies are, how many stars are formed in the galaxies, and how this depends on how much dark matter there is surrounding those galaxies," said Viola.

Viola explained that measuring dark matter content in galaxies is key to understanding the formation and evolution of galaxies. "We found that most of the time, the brightest galaxies were at the centre of this dark matter halo surrounding the groups," said Viola.

This, said lead researcher at Leiden Observatory in the Netherlands, Koen Kuijken, supports predictions of galaxy formation theory whereby galaxies are sucked into groups and pile up in the centre of dark matter clumps.

Currently, KiDS is one of three survey projects along with the Dark Energy Survey and the survey conducted by astronomers from America and Japan, trying to find an explanation for the expansion of our universe.

Viola told me that though KiDS had the smallest telescope (2.5 metres); it had the highest image resolution. "To measure this gravitational lensing effect you really want to have excellent image quality–our survey better in this respect," he said. Viola explained how the three teams could compare results and come to an understanding of the formation of galaxies and evolution of the universe together. "This is a very exciting time with all these different teams working, or competing if you want, on this science," he said.