Phinney has also showed how measured properties of cluster pulsars can be used to test theories of the dynamical evolution of clusters, and to determine the number of massive stars present in the clusters when they formed some 15 billion years ago. Postdoctoral fellow Andrew Melatos is investigating particle acceleration in the strong electromagnetic waves and winds of pulsars. These allow recent observations of pulsar companions with Keck telescope and HST to be interpreted, and show that the spin-ages of pulsars are not good estimates of the true time since recycling of millisecond pulsars. Other recent activities of Phinney's group include studies of the origin of magnetic fields and ionizing photons in the early universe, star formation and stellar collisions in galactic nuclei, and the surface physics of neutron stars and irradiated neutron star companions. Goldreich and former research fellow Sridhar, have been investigating interstellar turbulence, manifested in the scintillation of small angular diameter radio sources.
Differential refraction is due to turbulent fluctuations of the electron number density.
The physics is analogous to that of the twinkling of stars seen through the Earth's atmosphere. The elongation of the images of strongly scattered radio sources suggests that the turbulence is anisotropic. Since existing theories of weak MHD turbulence are based on three-mode couplings, they must be discarded. They went on to show that weak turbulent cascades based on four-mode couplings inevitably terminate in strong turbulence. These insights led them to propose a unique spectrum for strong Alfvenic turbulence.