Dynamical ejecta and nucleosynthetic yields from eccentric binary neutron-star mergers

Abstract

With the recent advent of multi-messenger gravitational-wave astronomy and in anticipation of more sensitive, next-generation gravitational-wave detectors, we investigate the dynamics, gravitational-wave emission, and nucleosynthetic yields of numerous eccentric binary neutron-star mergers having different equations of state. For each equation of state we vary the orbital properties around the threshold of immediate merger, as well as the binary mass ratio. In addition to a study of the gravitational-wave emission including f -mode oscillations before and after merger, we couple the dynamical ejecta output from the simulations to the nuclear-reaction network code SkyNet to compute nucleosynthetic yields and compare to the corresponding results in the case of a quasi-circular merger. We find that the amount and velocity of dynamically ejected material is always much larger than in the quasi-circular case, reaching maximal values of Mej,max ∼ 0.1 M and vmax/c ∼ 0.75. At the same time, the properties of this material are rather insensitive to the details of the orbit, such as pericenter distance or post-encounter apoastron distance. Furthermore, while the composition of the ejected matter depends on the orbital parameters and on the equation of state, the relative nucleosynthetic yields do not, thus indicating that kilonova signatures could provide information on the orbital properties of dynamically captured neutron-star binaries.PACS numbers: 04.25. Dm, 04.25.dk, 04.30.Db, 04.40.Dg, 95.30.Lz, 95.30.Sf, 97.60.Jd 97.60.Lf 26.60Kp 26.60Dd arXiv:1807.03795v2 [gr-qc]

Impact of High Spins on the Ejection of Mass in GW170817

“…2), we find that mass ejection is significantly suppressed, up to one order of magnitude for the TNTYST EOS. Furthermore, the ejection is strongly beamed towards the equator, a clear indication that the origin of the mass ejection is purely tidal, consistent with the fact of the two stars having a significantly reduced relative velocity at merger, in analogy with what happens in eccentric mergers (Radice et al 2016;Papenfort et al 2018). An important difference with respect to the other two cases is that the ejecta are mainly neutron rich and even the polar regions feature significantly smaller electron fractions.…”

“…Hence, having a very accurate modelling of the mass ejection and its origins is of great importance and several studies have already been made to elucidate the ejection mechanism Corresponding author: Elias R. Most emost@itp.uni-frankfurt.de and quantify the various ejection channels. Numerical simulations classify the ejection in terms of matter that is dynamically ejected (Hotokezaka et al 2013;Bauswein et al 2013;Radice et al 2016Radice et al , 2018Palenzuela et al 2015;Lehner et al 2016;Sekiguchi et al 2015Sekiguchi et al , 2016Dietrich & Ujevic 2017;Dietrich et al 2017b,a;Bovard et al 2017;Papenfort et al 2018) during or shortly after the merger of the two stars, and in terms of matter that is ejected secularly (Siegel & Metzger 2017;Fernández et al 2018;Fujibayashi et al 2017), that is, on timescales 100 ms. Of these two channels, the second component is not yet very well understood, mostly due to the lack of long-term three dimensional studies, although notable exceptions exist, starting either from simplified initial conditions (Siegel & Metzger 2017;Fernández et al 2018) or being restricted to two spatial dimensions . In comparison, the dynamically ejected mass component has been explored in far greater detail, using either fully consistent microphysical descriptions at finite temperature and in full general relativity (Radice et al 2016(Radice et al , 2018Lehner et al 2016;Sekiguchi et al 2016;Bovard et al 2017), or in approximations of general relativity (Bauswein et al 2013), or using a simplified microphysics treatment (Dietrich et al 2017b,a;Hotokezaka et al 2013;Ciolfi et al 2017), together with analytical expressions that try to com-bine the abundance of data available (Dietrich & Ujevic 2017).…”

Beyond second-order convergence in simulations of magnetized binary neutron stars with realistic microphysics

“…2.1.2, but where for one set the high order correction (16) is switched off. This approach using high order reconstruction combined with an HLL Riemann solver at overall second-order convergence is commonly used when modelling of neutron star mergers and their remnants (Reisswig et al 2013;Muhlberger et al 2014;Foucart et al 2016;Hossein Nouri et al 2018;Radice et al 2018;Papenfort et al 2018) and hence allows us to draw conclusion directly relevant for existing and future studies of neutron star mergers.…”

Precursor flares of short gamma-ray bursts from crust yielding due to tidal resonances in coalescing binaries of rotating, magnetized neutron stars

“…Note that the eigenfrequencies (26) are negative in the inertial frame (4), thus indicating that the modes are subject to the gravitational radiation (CFS) instability [88][89][90]. The (rotating frame) frequencies of the f -(black curves) and r-(red, dashed curves) modes, as functions of spin frequency ν up until the secular stability limit ν 775 Hz, are shown in Figure 2.…”