Magnetized Binary Neutron Star Mergers: Simulations in Full General Relativity

         Zachariah B. Etienne
         Yuk Tung Liu
         Stuart L. Shapiro
         Keisuke Taniguchi

University of Illinois at Urbana-Champaign

ABSTRACT

Binary neutron stars (NSNSs) are expected to be among the leading sources of gravitational waves observable by ground-based laser interferometers and may be the progenitors of short-hard gamma ray bursts. We present a series of general relativistic NSNS coalescence simulations both for unmagnetized and magnetized stars. We adopt quasiequilibrium initial data for circular, irrotational binaries constructed in the conformal thin-sandwich (CTS) framework. We adopt the BSSN formulation for evolving the metric and a high-resolution shock-capturing scheme to handle the magnetohydrodynamics. Our simulations of unmagnetized binaries confirm the results of Shibata, Taniguchi and Uryu (2003). In cases in which the mergers result in a prompt collapse to a black hole, we are able to use puncture gauge conditions to extend the evolution and determine the mass of the material that forms a disk. We find that the disk mass is less than 2% of the total mass in all cases studied. We then add a small poloidal magnetic field to the initial configurations and study the subsequent evolution. For cases in which the remnant is a hypermassive neutron star, we see measurable differences in both the amplitude and phase of the gravitational waveforms following the merger. For cases in which the remnant is a black hole surrounded by a disk, the disk mass and the gravitational waveforms are about the same as the unmagnetized cases. Magnetic fields substantially affect the long-term, secular evolution of a hypermassive neutron star (driving `delayed collapse') and an accretion disk around a nascent black hole.

Phys. Rev. D77 084002 (2008), astro_ph/0803.4193v2

Initial Stellar Models

M1414 (M/R)∞ = 0.14, mass ratio q=1.00

M1616 (M/R)∞ = 0.16, mass ratio q=1.00

M1418 (M/R)∞ = 0.14, (M/R)∞ = 0.18, mass ratio q= 0.855

Comparisons

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University of Illinois at Urbana-Champaign

last updated 22 Feb. 09 by AH