Dark matter found in Milky Way’s core

S. Brunier/ESO

Dark matter found in Milky Way’s core

Most of the material of the universe is dark matter—stuff we can’t see, though we can still feel its gravity. It was discovered in the 1970s when astronomer Vera Rubin showed that stars in the outer regions of spiral galaxies, far from the center, were moving faster than they should be. This suggested there was some sort of unseen mass in a “halo” around the galaxy. But physicists disagree over whether all this dark matter is at the margin or if there is some in a galaxy’s core. Now, a team of researchers has attempted to answer that question for the Milky Way (pictured). They collected all the data they could find about stellar speeds in the inner regions of our home galaxy to see how they varied with distance from the center, they report online today in Nature Physics. Then they took the best models for how much normal matter there is throughout the galaxy and calculated how fast you would expect stars to be moving if only that normal matter was pulling on them. They found that the measured speeds and calculated speeds didn’t agree, demonstrating that dark matter does indeed play a role in the inner galaxy. The researchers hope their studies will help narrow down searches for the nature of dark matter as well as aid the understanding of galaxy formation.