JOIN USAstronomers have found large amounts of invisible “dark matter” near the Sun.The finding is consistent with the theory that the Milky Way Galaxy 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.
Astronomers at the University of Zurich, the ETH Zurich, the University of Leicester and NAOC Beijing have also found tantalizing hints of a new dark matter component in our galaxy.
Dark matter was first proposed by the Swiss astronomer Fritz Zwicky in the 1930s. He 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 nearly twice what could be explained by the presence of stars and gas alone.
In the intervening decades, astronomers developed a theory of dark matter and structure formation that explains the properties of clusters and galaxies in the universe, but the amount of dark matter in the solar neighbourhood has remained more mysterious.
For decades after Oort’s measurement, studies found three to six times more dark matter than expected. Then last year new data and a new method claimed far less than expected. The community was left puzzled, generally believing that the observations and analyzes simply weren’t sensitive enough to perform a reliable measurement.
In this latest study, the researchers are much more confident in their measurement and its uncertainties. This is because they used a state-of-the-art simulation of our galaxy to test their mass-measuring technique before applying it to real data. This threw up a number of surprises.
They found that standard techniques used over the past 20 years were biased, always tending to underestimate the amount of dark matter. They then devised a new unbiased technique that recovered the correct answer from the simulated data.
Applying their technique to the positions and velocities of thousands of orange K dwarf stars near the Sun, they obtained a new measure of the local dark matter density. “We are 99 percent confident that there is dark matter near the Sun.
In fact, our favoured dark matter density is a little high. There is a 10 percent chance that this is merely a statistical fluke. But with 90 percent confidence, we find more dark matter than expected,” said Lead author Silvia Garbari.