  Gravitational waves are predicted by the general theory of relativity. In [6]
D. Christodoulou showed that gravitational waves have a nonlinear memory. We
proved in [3] that the electromagnetic field contributes at highest order to
the nonlinear memory effect of gravitational waves. In the present paper, we
study this electromagnetic Christodoulou memory effect and compute it for
binary neutron star mergers. These are typical sources of gravitational
radiation. During these processes, not only mass and momenta are radiated away
in form of gravitational waves, but also very strong magnetic fields are
produced and radiated away. Thus the observed effect on test masses of a laser
interferometer gravitational wave detector will be enlarged by the contribution
of the electromagnetic field. Therefore, the present results are important for
the planned experiments. Looking at the null asymptotics of spacetimes, which
are solutions of the Einstein-Maxwell (EM) equations, we derived in [3] the
electromagnetic Christodoulou memory effect. Moreover, our results allow to
answer astro- physical questions, as the knowledge about the amount of energy
radiated away in a neutron star binary merger enables us to gain information
about the source of the gravitational waves.
