Magnetohydrodynamic simulations of eccentric binary neutron star mergers

Highly eccentric binary neutron star mergers exhibit unique dynamical and observational signatures compared to quasicircular ones in terms of their gravitational wave signal and the ejection of matter, leading to different electromagnetic counterparts. In this article, we present general relativistic magnetohydrodynamic simulations of binary neutron star systems on highly eccentric orbits. While in quasicircular binaries, the influence of the magnetic field is too weak to affect the general premerger dynamics, the close encounters in eccentric systems could potentially trigger magnetohydrodynamic instabilities. Therefore, we investigate possible effects before, during, and after the merger for a total of three different systems with varying initial eccentricity. We study the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mi>f</a:mi></a:mrow></a:math>-mode oscillations excited by tidal interaction in close encounters and find good agreement with predicted <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>f</c:mi></c:math>-mode frequency estimates. However, our simulations reveal no significant differences compared to results neglecting the magnetic field. Although we observe a rearrangement of the poloidal structure of the magnetic field inside the stars, there is no relevant increase in the magnetic energy during the encounters. Also, during the merger, the amplification of the magnetic field seems to be largely independent of the eccentricity in our systems. Consistent with studies of merging nonmagnetized binary neutron stars, we find a correlation between eccentricity and mass ejection, with a higher impact parameter leading to a larger amount of unbound material.