Case weakens for antimatter sign of dark matter

A long debate over a mysterious surplus of antimatter—and whether it’s a sign of dark matter—may be coming to an anticlimactic end. For more than a decade, multiple experiments have found an unexpected excess in the number of high-energy antielectrons, or positrons, in space, and some physicists suggested it could be due to particles of dark matter annihilating one another. Others countered with a more mundane explanation: The positrons come from rapidly rotating neutron stars, or pulsars. Now, a team of theorists has bolstered that more prosaic explanation, showing in detail that pulsars can indeed produce most or all of the excess.