Are these two classes of distant objects related? Evolution of dense stellar clusters, so crowded with stars that collisions occur, yielding more massive stars and supernovae, could be the common origin of them both.
Intense, coherent laser beams permit study of media polarized as the square or third power of field strength. Phenomena include harmonic generation, modulation, stimulated scattering and self‐focusing. Newly available tools utilize picosecond optical pulses.
Scattering of electrons on nucleons and electron‐positron scattering in colliding‐beam experiments give a measure of the size and charge distribution of the proton, neutron and pion. Theoretical understanding is fairly advanced for the pion but still uncertain for the nucleons.