There's Plenty Of Dark Matter Near The Sun
August 9, 2012

Dark Matter Exists In Abundance Near The Sun

April Flowers for - Your Universe Online

Astronomers at the University of Zurich, ETH Zurich, the University of Leicester and NOAC Beijing have found large amounts of invisible "dark matter" near the Sun. They also found tantalizing hints of a new dark matter component within our own galaxy.

The study results, which will be published in the journal Monthly Notices of the Royal Astronomical Society, are consistent with the theory that the Milky Way is surrounded by a massive halo of dark matter, but this is the first study of its kind to use a method rigorously tested against mock data from high quality simulations.

Swiss astronomer, Fritz Zwicky, first proposed the theory of dark matter in the 1930's. Zwicky found that clusters of galaxies were filled with a mysterious dark matter that kept them from flying apart. At nearly the same time, Jan Oort in the Netherlands discovered that the density of matter near the Sun was almost twice what could be explained by the presence of stars and gas alone.

Since then, astronomers developed a theory of dark matter and structure formation that explains the properties of clusters and galaxies in the Universe, but the sheer amount of dark matter in our own solar neighborhood has remained elusive.

There has been controversy of course. Since Oort's measurements, studies have found 3-6 times more dark matter than expected. Then last year, new data and a new method claimed far less than expected. The scientific community was left puzzled, generally believing that the observations and analysis simply weren't sensitive enough to perform a reliable measurement.

This most recent study, however, is based on a new technique. Led by the University of Zurich, the research team used a state-of-the-art simulation of the Milky Way to test their mass-measuring method before applying it to real data. These simulations created a number of new surprises. Specifically, the team noticed that past investigative techniques were biased, always tending to underestimate the amount of dark matter. The team developed a new unbiased technique that recovered the correct answer from the simulated data and applied the technique to the positions and velocities of thousands of orange K dwarf stars near the Sun. This allowed the researchers to obtain a new measure of the local dark matter density.

"We are 99% confident that there is dark matter near the Sun," says the lead author Silvia Garbari. "In fact, if anything, the authors' favored dark matter density is a little high: they find more dark matter than expected at 90% confidence. There is a 10% chance that this is merely a statistical fluke, but if future data confirms this high value, the implications are exciting. 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 and other scientists are placing their bets on dark matter being a new fundamental particle that interacts only very weakly with normal matter, but strong enough to be detected in experiments deep underground. An accurate measure of the local dark matter density is vital for such experiments.

According to co-author Prof George Lake, "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. 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."