Evolution versus variability in neutron star binaries

Abstract

In recent years, the discovery of orbital period changes and eclipses in binaries with neutron stars has led to a new wave of excitement over these systems. They have also led to speculation that the traditional views of x‐ray binary evolution may be incomplete. Here I briefly discuss the observed orbital period derivatives and possible analogies between these binaries and other types of compact binary. I conclude that stellar activity in a late‐type companion is the most likely cause for the anomalous orbital period changes, and that it is also a strong candidate for explaining the eclipse phenomenon in at least some observed systems.