Discovery could settle dark matter mystery

Posted by Emma Woollacott

Swiss astronomers say they've found large amounts of dark matter near the sun, by comparing high-quality simulations with real data.

For decades, there's been confusion. Back in the 1930s, Jan Oort in the Netherlands discovered that the density of matter near the sun was nearly twice what could be explained by normal matter.

Further studies indicated there was up to six times as much dark matter as expected.

However, last year new data and a new method indicated that there was actually far less than expected, leaving scientists scratching their heads.

Now, though, a team led by the University of Zürich has developed a new technique. The researchers used a state-of-the-art simulation of the Milky Way to test their mass-measuring method before applying it to real data.

And, they concluded, the standard techniques used over the past twenty years are biased, always tending to underestimate the amount of dark matter. Correcting for this and applying their technique to the positions and velocities of thousands of orange K dwarf stars near the Sun, they now have a new figure for local dark matter density.

"We are 99 percent confident that there is dark matter near the sun," says lead author Silvia Garbari.

"This could be the first evidence for a "disc" of dark matter in our Galaxy, as recently predicted by theory and numerical simulations of galaxy formation, or it could mean that the dark matter halo of our galaxy is squashed, boosting the local dark matter density."

Many physicists believe that dark matter is a new fundamental particle that interacts very weakly with normal matter - but just strongly enough to be detected in experiments deep underground. An accurate measure of the local dark matter density could help establish if this is the case.

"If dark matter is a fundamental particle, billions of these particles will have passed through your body by the time your finish reading this article," says co-author George Lake.

"Experimental physicists hope to capture just a few of these particles each year in experiments like XENON and CDMS currently in operation. Knowing the local properties of dark matter is the key to revealing just what kind of particle it consists of."