Electromagnetic and Gravitational Outputs from Binary-Neutron-Star Coalescence

The late stage of an inspiraling neutron-star binary gives rise to strong gravitational wave emission due to its highly dynamic, strong gravity. Moreover, interactions between the stellar magnetospheres can produce considerable electromagnetic radiation. We study this scenario using fully general relativistic, resistive magnetohydrodynamic simulations. We show that these interactions extract kinetic energy from the system, dissipate heat, and power radiative Poynting flux, as well as develop current sheets. Our results indicate that this power can (i) outshine pulsars in binaries, (ii) display a distinctive angular- and time-dependent pattern, and (iii) radiate within large opening angles. These properties suggest that some binary neutron-star mergers are ideal candidates for multimessenger astronomy.

Figure 1

Magnetic field configurations (field lines) and current sheets (orange regions) for—from left to right—the $U/D$, $U/U$, and $U/u$ cases at time $t=-1.7\mathrm{ms}$. In all panels, the magnetic field strength varies from ${10}^8$ (blue regions) to ${10}^{11}$ (red regions) G. The current sheet for the $U/U$ case arises far outside the binary, whereas that for the $U/D$ case arises between the stars and spirals outward. A trailing dissipation tail is induced in the $U/u$ case.

Figure 2

Representative snapshots of the electromagnetic energy flux at $t=-2.9\mathrm{ms}$ (left column) and currents (arrows) and charge density [negative (positive) shaded in red (blue)] at $t=-0.5\mathrm{ms}$ (right column) for the $U/D$, $U/U$, and $U/u$ cases (top, middle, and bottom panels, respectively). The $U/D$ and $U/U$ cases display currents extending significantly in both vertical directions, together with EM radiation mainly directed along the shear layer. In contrast, the currents are mostly localized in between the stars for the $U/u$ case, with an energy flux concentrated near the equatorial plane. The color scales for the energy flux are arbitrary (with green to red spanning 3 orders of magnitude in scale; see Fig. 3 for total luminosity vs time for each case). For comparison among the three cases, we note that the $U/D$ ($U/U$) case is 3 (2) orders of magnitude larger than the $U/u$ case.

Figure 3

Gravitational (right axis) and electromagnetic (left axis) luminosities for the three configurations vs time. Three curves illustrating $L\propto {\Omega }^p$ with $p=\{3/2,14/3,12\}$ are shown as guidance.