Electrically Neutral Quark Matter

should lie at the heart of neutron stars, conclude two MIT theorists. It has long been thought that, in the exotic high-density environment within a neutron star, equal numbers of “up” and “down” quarks (with respective charges of + $2 3$  e and − $1 3$  e) dominate, with a small admixture of “strange” quarks (− $1 3$  e). The quark matter would thus have an overall positive charge and would draw electrons into it. Now, however, Krishna Rajagopal and Frank Wilczek have demonstrated that all three quark varieties will coexist in equal numbers in such an environment, meaning that the material is an electrically neutral insulator, free of electrons. Two consequences are that a neutron star’s core would be unable to anchor magnetic fields and that the time distribution of neutrinos from a supernova could be altered. (K. Rajagopal, F. Wilczek, Phys. Rev. Lett. 86,...