Along with bremsstrahlung (“BREMSH-trah-lung”) and the Urca process, the breaking and formation of these things in the PBF process is used to explain why a star’s surface temperature may be too low for its age. In 2021, Grinenko et al. reported the observation of a new state of matter made of twinned examples of these things, which they called a quartic bosonic metal. Skyrmions can form tightly bound examples of these things when two sheets of graphene are stacked and twisted. Experimental evidence for these states was given when mass was found to have an inverse relationship with transition temperature in the isotope effect. Electron-phonon (10[1])interactions cause the formation of these states below the critical temperature in materials like YBCO. For 10 points, name these bound states used in BCS theory to explain superconductivity. ■END■