First 100 ms of a long-lived magnetized neutron star formed in a binary neutron star merger Article Swipe
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· 2019
· Open Access
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· DOI: https://doi.org/10.1103/physrevd.100.023005
· OA: W2942425346
The recent multimessenger observation of the short gamma-ray burst (SGRB) GRB\n170817A together with the gravitational wave (GW) event GW170817 provides\nevidence for the long-standing hypothesis associating SGRBs with binary neutron\nstar (BNS) mergers. The nature of the remnant object powering the SGRB, which\ncould have been either an accreting black hole (BH) or a long-lived magnetized\nneutron star (NS), is, however, still uncertain. General relativistic\nmagnetohydrodynamic (GRMHD) simulations of the merger process represent a\npowerful tool to unravel the jet launching mechanism, but so far most\nsimulations focused the attention on a BH as the central engine, while the\nlong-lived NS scenario remains poorly investigated. Here, we explore the latter\nby performing a GRMHD BNS merger simulation extending up to ~100 ms after\nmerger, much longer than any previous simulation of this kind. This allows us\nto (i) study the emerging structure and amplification of the magnetic field and\nobserve a clear saturation at magnetic energy $E_\\mathrm{mag} \\sim 10^{51}$\nerg, (ii) follow the magnetically supported expansion of the outer layers of\nthe remnant NS and its evolution into an ellipsoidal shape without any\nsurrounding torus, and (iii) monitor density, magnetization, and velocity along\nthe axis, observing no signs of jet formation. We also argue that the\nconditions at the end of the simulation disfavor later jet formation on\nsubsecond timescales if no BH is formed. Furthermore, we examine the rotation\nprofile of the remnant, the conversion of rotational energy associated with\ndifferential rotation, the overall energy budget of the system, and the\nevolution of the GW frequency spectrum. Finally, we perform an additional\nsimulation where we induce the collapse to a BH ~70 ms after merger, in order\nto gain insights on the prospects for massive accretion tori in case of a late\ncollapse. We find that...\n
