How ‘Dark’ Is Dark Matter?

Dark matter has been described as “dark” because scientists believe the mysterious matter only interacts with gravity, causing it to be invisible. In a study out this week in Monthly Notices of the Royal Astronomical Society, researchers observed dark matter potentially interacting with something else—itself. Astrophysicist Richard Massey says that “this could be the first dynamical evidence that dark matter notices the world around it. Dark matter may not be completely ‘dark’ after all.”