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17 Research products, page 1 of 2

  • Canada
  • Natural Sciences and Engineering Research Council of Canada
  • Gravitational Radiation and Relativistic Astrophysics

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  • Open Access English
    Authors: 
    Hinderer, Tanja; Nissanke, Samaya; Foucart, Francois; Hotokezaka, Kenta; Vincent, Trevor; Kasliwal, Mansi; Schmidt, Patricia; Williamson, Andrew R.; Nichols, David; Duez, Matthew; +3 more
    Project: NSERC , NSF | Gravitational Radiation a... (1404569), NSF | Gravitational Radiation a... (1708213), NSF | Mergers, Stars, and Disks... (1806207), NSF | Maximizing Science Output... (1708212), NSF | PIRE: GROWTH: Global Rela... (1545949), NWO | Precision Gravity: black ... (680-47-460)

    The discovery of GW170817 with gravitational waves (GWs) and electromagnetic (EM) radiation is prompting new questions in strong-gravity astrophysics. Importantly, it remains unknown whether the progenitor of the merger comprised two neutron stars (NSs), or a NS and a black hole (BH). Using new numerical-relativity simulations and incorporating modeling uncertainties we produce novel GW and EM observables for NS-BH mergers with similar masses. A joint analysis of GW and EM measurements reveals that if GW170817 is a NS-BH merger, <40% of the binary parameters consistent with the GW data are compatible with EM observations. Comment: 8 pages

  • Open Access English
    Authors: 
    Foucart, Francois; Duez, Matthew D.; Hebert, Francois; Kidder, Lawrence E.; Kovarik, Phillip; Pfeiffer, Harald P.; Scheel, Mark A.;
    Project: NSF | Mergers, Stars, and Disks... (1806207), NSF | Simulating the Multi-Mess... (1806278), NSF | Elements:Collaborative Pr... (1931280), NSF | Gravitational Radiation a... (1708213), NSF | WoU-MMA: Research in Blac... (1912081), NSERC , NSF | MRI: Acquisition of a Com... (1919310)

    Neutrino transport and neutrino-matter interactions are known to play an important role in the evolution of neutron star mergers, and of their post-merger remnants. Neutrinos cool remnants, drive post-merger winds, and deposit energy in the low-density polar regions where relativistic jets may eventually form. Neutrinos also modify the composition of the ejected material, impacting the outcome of nucleosynthesis in merger outflows and the properties of the optical/infrared transients that they power (kilonovae). So far, merger simulations have largely relied on approximate treatments of the neutrinos (leakage, moments) that simplify the equations of radiation transport in a way that makes simulations more affordable, but also introduces unquantifiable errors in the results. To improve on these methods, we recently published a first simulation of neutron star mergers using a low-cost Monte-Carlo algorithm for neutrino radiation transport. Our transport code limits costs in optically thick regions by placing a hard ceiling on the value of the absorption opacity of the fluid, yet all approximations made within the code are designed to vanish in the limit of infinite numerical resolution. We provide here an in-depth description of this algorithm, of its implementation in the SpEC merger code, and of the expected impact of our approximations in optically thick regions. We argue that the latter is a subdominant source of error at the accuracy reached by current simulations, and for the interactions currently included in our code. We also provide tests of the most important features of this code. Comment: 32p, 1 table and 14 figures; Accepted by ApJ

  • Open Access English
    Authors: 
    Brege, Wyatt; Duez, Matthew D.; Foucart, Francois; Deaton, M. Brett; Caro, Jesus; Hemberger, Daniel A.; Kidder, Lawrence E.; O'Connor, Evan; Pfeiffer, Harald P.; Scheel, Mark A.;
    Project: NSF | MRI-R2: Acquisition of a ... (0960291), NSF | Numerical Simulations of ... (1402916), NSF | Collaborative Research: P... (1440083), NSF | Gravitational Radiation a... (1404569), NSERC , NSF | Gravitational Radiation a... (1708213), NSF | Maximizing Science Output... (1708212)

    Each of the potential signals from a black hole-neutron star merger should contain an imprint of the neutron star equation of state: gravitational waves via its effect on tidal disruption, the kilonova via its effect on the ejecta, and the gamma ray burst via its effect on the remnant disk. These effects have been studied by numerical simulations and quantified by semi-analytic formulae. However, most of the simulations on which these formulae are based use equations of state without finite temperature and composition-dependent nuclear physics. In this paper, we simulate black hole-neutron star mergers varying both the neutron star mass and the equation of state, using three finite-temperature nuclear models of varying stiffness. Our simulations largely vindicate formulae for ejecta properties but do not find the expected dependence of disk mass on neutron star compaction. We track the early evolution of the accretion disk, largely driven by shocking and fallback inflow, and do find notable equation of state effects on the structure of this early-time, neutrino-bright disk. Comment: 10 pages, 11 figures, submitted to Phys. Rev. D

  • Open Access English
    Authors: 
    Foucart, Francois; Chernoglazov, Alexander; Boyle, Michael; Hinderer, Tanja; Miller, Max; Moxon, Jordan; Scheel, Mark A.; Deppe, Nils; Duez, Matthew D.; Hebert, Francois; +3 more
    Project: NSERC , NSF | Gravitational Radiation a... (1708213), NSF | Simulating the Multi-Mess... (1806278), NSF | Mergers, Stars, and Disks... (1806207), NSF | WoU-MMA: Research in Blac... (1912081), NSF | Elements:Collaborative Pr... (1931280)

    The availability of accurate numerical waveforms is an important requirement for the creation and calibration of reliable waveform models for gravitational wave astrophysics. For black hole-neutron star binaries, very few accurate waveforms are however publicly available. Most recent models are calibrated to a large number of older simulations with good parameter space coverage for low-spin non-precessing binaries but limited accuracy, and a much smaller number of longer, more recent simulations limited to non-spinning black holes. In this paper, we present long, accurate numerical waveforms for three new systems that include rapidly spinning black holes, and one precessing configuration. We study in detail the accuracy of the simulations, and in particular perform for the first time in the context of BHNS binaries a detailed comparison of waveform extrapolation methods to the results of Cauchy Characteristic Extraction. The new waveforms have $0.99$) for binaries seen face-on. For edge-on observations, particularly for precessing systems, disagreements between models and simulations increase, and models that include precession and/or higher-order modes start to perform better than BHNS models that currently lack these features. Comment: 16p, 14 figs, 2 tables; To be submitted to PRD

  • Open Access English
    Authors: 
    Duez, Matthew D.; Knight, Alexander; Foucart, Francois; Haddadi, Milad; Jesse, Jerred; Hebert, Francois; Kidder, Lawrence E.; Pfeiffer, Harald P.; Scheel, Mark A.;
    Project: NSERC , NSF | Gravitational Radiation a... (1708213), NSF | WoU-MMA: Research in Blac... (1912081), NSF | Maximizing Science Output... (1708212), NSF | Simulating the Multi-Mess... (1806278), NSF | Mergers, Stars, and Disks... (1806207)

    The main problems of nonvacuum numerical relativity, compact binary mergers and stellar collapse, involve hydromagnetic instabilities and turbulent flows, so that kinetic energy at small scales have mean effects at large scale that drive the secular evolution. Notable among these effects is momentum transport. We investigate two models of this transport effect, a relativistic Navier-Stokes system and a turbulent mean stress model, that are similar to all of the prescriptions that have been attempted to date for treating subgrid effects on binary neutron star mergers and their aftermath. Our investigation involves both stability analysis and numerical experimentation on star and disk systems. We also begin the investigation of the effects of particle and heat transport on post-merger simulations. We find that correct handling of turbulent heating can be important for avoiding unphysical instabilities. Given such appropriate handling, the evolution of a differentially rotating star and the accretion rate of a disk are reassuringly insensitive to the choice of prescription. However, disk outflows can be sensitive to the choice of method, even for the same effective viscous strength. We also consider the effects of eddy diffusion in the evolution of an accretion disk and show that it can interestingly affect the composition of outflows. Comment: 15 pagers, 11 figures

  • Open Access English
    Authors: 
    Jesse, Jerred; Duez, Matthew D.; Foucart, Francois; Haddadi, Milad; Knight, Alexander L.; Cadenhead, Courtney L.; Hebert, Francois; Kidder, Lawrence E.; Pfeiffer, Harald P.; Scheel, Mark A.;
    Project: NSERC , NSF | Gravitational Radiation a... (1708213), NSF | Simulating the Multi-Mess... (1806278), NSF | WoU-MMA: Research in Blac... (1912081), NSF | Mergers, Stars, and Disks... (1806207)

    We describe a method of implementing the axisymmetric evolution of general-relativistic hydrodynamics and magnetohydrodynamics through modification of a multipatch grid scheme. In order to ease the computational requirements required to evolve the post-merger phase of systems involving binary compact massive objects in numerical relativity, it is often beneficial to take advantage of these system's tendency to rapidly settle into states that are nearly axisymmetric, allowing for 2D evolution of secular timescales. We implement this scheme in the spectral Einstein code and show the results of application of this method to four test systems including viscosity, magnetic fields, and neutrino radiation transport. Our results show that this method can be used to quickly allow already existing 3D infrastructure that makes use of local coordinate system transformations to be made to run in axisymmetric 2D with the flexible grid creation capabilities of multipatch methods. Our code tests include a simple model of a binary neutron star postmerger remnant, for which we confirm the formation of a massive torus which is a promising source of post-merger ejecta. Comment: 33 pages, 11 figures

  • Open Access English
    Authors: 
    Foucart, Francois; Duez, Matthew D.; Gudinas, Alana; Hebert, Francois; Kidder, Lawrence E.; Pfeiffer, Harald P.; Scheel, Mark A.;
    Project: NSERC , NSF | MRI: Aquisition of Comput... (1229408), NSF | Mergers, Stars, and Disks... (1806207), NSF | Simulating the Multi-Mess... (1806278), NSF | Gravitational Radiation a... (1708213), NSF | Sustained-Petascale In Ac... (1238993), NSF | Leadership Class Scientif... (0725070), NSF | WoU-MMA: Research in Blac... (1912081)

    High-accuracy numerical simulations of merging neutron stars play an important role in testing and calibrating the waveform models used by gravitational wave observatories. Obtaining high-accuracy waveforms at a reasonable computational cost, however, remains a significant challenge. One issue is that high-order convergence of the solution requires the use of smooth evolution variables, while many of the equations of state used to model the neutron star matter have discontinuities, typically in the first derivative of the pressure. Spectral formulations of the equation of state have been proposed as a potential solution to this problem. Here, we report on the numerical implementation of spectral equations of state in the Spectral Einstein Code. We show that, in our code, spectral equations of state allow for high-accuracy simulations at a lower computational cost than commonly used `piecewise polytrope' equations state. We also demonstrate that not all spectral equations of state are equally useful: different choices for the low-density part of the equation of state can significantly impact the cost and accuracy of simulations. As a result, simulations of neutron star mergers present us with a trade-off between the cost of simulations and the physical realism of the chosen equation of state. Comment: Submitted to PRD, 13p, 7 figures, 3 tables

  • Open Access
    Authors: 
    Wyatt Brege; Matthew D. Duez; Francois Foucart; M. Brett Deaton; Jesus Caro; Daniel A. Hemberger; Lawrence E. Kidder; Evan O'Connor; Harald P. Pfeiffer; Mark A. Scheel;
    Publisher: American Physical Society (APS)
    Country: United States
    Project: NSF | Gravitational Radiation a... (1708213), NSF | Numerical Simulations of ... (1402916), NSF | MRI-R2: Acquisition of a ... (0960291), NSF | Maximizing Science Output... (1708212), NSF | Mergers, Stars, and Disks... (1806207), NSF | Collaborative Research: P... (1440083), NSF | Gravitational Radiation a... (1404569), NSERC

    Each of the potential signals from a black hole-neutron star merger should contain an imprint of the neutron star equation of state: gravitational waves via its effect on tidal disruption, the kilonova via its effect on the ejecta, and the gamma ray burst via its effect on the remnant disk. These effects have been studied by numerical simulations and quantified by semi-analytic formulae. However, most of the simulations on which these formulae are based use equations of state without finite temperature and composition-dependent nuclear physics. In this paper, we simulate black hole-neutron star mergers varying both the neutron star mass and the equation of state, using three finite-temperature nuclear models of varying stiffness. Our simulations largely vindicate formulae for ejecta properties but do not find the expected dependence of disk mass on neutron star compaction. We track the early evolution of the accretion disk, largely driven by shocking and fallback inflow, and do find notable equation of state effects on the structure of this early-time, neutrino-bright disk. 10 pages, 11 figures, submitted to Phys. Rev. D

  • Open Access
    Authors: 
    Tanja Hinderer; Samaya Nissanke; Francois Foucart; Kenta Hotokezaka; Trevor Vincent; Mansi M. Kasliwal; Patricia Schmidt; A. R. Williamson; David A. Nichols; Matthew D. Duez; +3 more
    Publisher: American Physical Society (APS)
    Countries: United States, Netherlands, Netherlands, Netherlands, Netherlands, United Kingdom
    Project: NSERC , NSF | Maximizing Science Output... (1708212), NSF | Gravitational Radiation a... (1708213), NWO | Precision Gravity: black ... (680-47-460), NSF | Mergers, Stars, and Disks... (1806207), NSF | PIRE: GROWTH: Global Rela... (1545949), NSF | Gravitational Radiation a... (1404569)

    The discovery of GW170817 with gravitational waves (GWs) and electromagnetic (EM) radiation is prompting new questions in strong-gravity astrophysics. Importantly, it remains unknown whether the progenitor of the merger comprised two neutron stars (NSs), or a NS and a black hole (BH). Using new numerical-relativity simulations and incorporating modeling uncertainties we produce novel GW and EM observables for NS-BH mergers with similar masses. A joint analysis of GW and EM measurements reveals that if GW170817 is a NS-BH merger, <40% of the binary parameters consistent with the GW data are compatible with EM observations. 8 pages

  • Open Access English
    Authors: 
    Foucart, Francois; Duez, Matthew D.; Hinderer, Tanja; Caro, Jesus; Williamson, Andrew R.; Boyle, Michael; Buonanno, Alessandra; Haas, Roland; Hemberger, Daniel A.; Kidder, Lawrence E.; +2 more
    Project: NSERC , NSF | Simulating the Multi-Mess... (1806278), NSF | MRI-R2: Acquisition of a ... (0960291), NSF | Mergers, Stars, and Disks... (1806207), NSF | Leadership Class Scientif... (0725070), NSF | Sustained-Petascale In Ac... (1238993), NSF | Inter-agency Workshop for... (1551592), NSF | Gravitational Radiation a... (1708213)

    Gravitational waveforms from numerical simulations are a critical tool to test and analytically calibrate the waveform models used to study the properties of merging compact objects. In this paper, we present a series of high-accuracy waveforms produced with the SpEC code for systems involving at least one neutron star. We provide for the first time waveforms with sub-radian accuracy over more than twenty cycles for low-mass black hole-neutron star binaries, including binaries with non-spinning objects, and binaries with rapidly spinning neutron stars that maximize the impact on the gravitational wave signal of the near-resonant growth of the fundamental excitation mode of the neutron star (f-mode). We also provide for the first time with SpEC a high-accuracy neutron star-neutron star waveform. These waveforms are made publicly available as part of the SxS catalogue. We compare our results to analytical waveform models currently implemented in data analysis pipelines. For most simulations, the models lie outside of the predicted numerical errors in the last few orbits before merger, but do not show systematic deviations from the numerical results: comparing different models appears to provide reasonable estimates of the modeling errors. The sole exception is the equal-mass simulation using a rapidly counter-rotating neutron star to maximize the impact of the excitation of the f-mode, for which all models perform poorly. This is however expected, as even the single model that takes f-mode excitation into account ignores the significant impact of the neutron star spin on the f-mode excitation frequency. Comment: 17p, 10 figures

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Include:
The following results are related to Canada. Are you interested to view more results? Visit OpenAIRE - Explore.
17 Research products, page 1 of 2
  • Open Access English
    Authors: 
    Hinderer, Tanja; Nissanke, Samaya; Foucart, Francois; Hotokezaka, Kenta; Vincent, Trevor; Kasliwal, Mansi; Schmidt, Patricia; Williamson, Andrew R.; Nichols, David; Duez, Matthew; +3 more
    Project: NSERC , NSF | Gravitational Radiation a... (1404569), NSF | Gravitational Radiation a... (1708213), NSF | Mergers, Stars, and Disks... (1806207), NSF | Maximizing Science Output... (1708212), NSF | PIRE: GROWTH: Global Rela... (1545949), NWO | Precision Gravity: black ... (680-47-460)

    The discovery of GW170817 with gravitational waves (GWs) and electromagnetic (EM) radiation is prompting new questions in strong-gravity astrophysics. Importantly, it remains unknown whether the progenitor of the merger comprised two neutron stars (NSs), or a NS and a black hole (BH). Using new numerical-relativity simulations and incorporating modeling uncertainties we produce novel GW and EM observables for NS-BH mergers with similar masses. A joint analysis of GW and EM measurements reveals that if GW170817 is a NS-BH merger, <40% of the binary parameters consistent with the GW data are compatible with EM observations. Comment: 8 pages

  • Open Access English
    Authors: 
    Foucart, Francois; Duez, Matthew D.; Hebert, Francois; Kidder, Lawrence E.; Kovarik, Phillip; Pfeiffer, Harald P.; Scheel, Mark A.;
    Project: NSF | Mergers, Stars, and Disks... (1806207), NSF | Simulating the Multi-Mess... (1806278), NSF | Elements:Collaborative Pr... (1931280), NSF | Gravitational Radiation a... (1708213), NSF | WoU-MMA: Research in Blac... (1912081), NSERC , NSF | MRI: Acquisition of a Com... (1919310)

    Neutrino transport and neutrino-matter interactions are known to play an important role in the evolution of neutron star mergers, and of their post-merger remnants. Neutrinos cool remnants, drive post-merger winds, and deposit energy in the low-density polar regions where relativistic jets may eventually form. Neutrinos also modify the composition of the ejected material, impacting the outcome of nucleosynthesis in merger outflows and the properties of the optical/infrared transients that they power (kilonovae). So far, merger simulations have largely relied on approximate treatments of the neutrinos (leakage, moments) that simplify the equations of radiation transport in a way that makes simulations more affordable, but also introduces unquantifiable errors in the results. To improve on these methods, we recently published a first simulation of neutron star mergers using a low-cost Monte-Carlo algorithm for neutrino radiation transport. Our transport code limits costs in optically thick regions by placing a hard ceiling on the value of the absorption opacity of the fluid, yet all approximations made within the code are designed to vanish in the limit of infinite numerical resolution. We provide here an in-depth description of this algorithm, of its implementation in the SpEC merger code, and of the expected impact of our approximations in optically thick regions. We argue that the latter is a subdominant source of error at the accuracy reached by current simulations, and for the interactions currently included in our code. We also provide tests of the most important features of this code. Comment: 32p, 1 table and 14 figures; Accepted by ApJ

  • Open Access English
    Authors: 
    Brege, Wyatt; Duez, Matthew D.; Foucart, Francois; Deaton, M. Brett; Caro, Jesus; Hemberger, Daniel A.; Kidder, Lawrence E.; O'Connor, Evan; Pfeiffer, Harald P.; Scheel, Mark A.;
    Project: NSF | MRI-R2: Acquisition of a ... (0960291), NSF | Numerical Simulations of ... (1402916), NSF | Collaborative Research: P... (1440083), NSF | Gravitational Radiation a... (1404569), NSERC , NSF | Gravitational Radiation a... (1708213), NSF | Maximizing Science Output... (1708212)

    Each of the potential signals from a black hole-neutron star merger should contain an imprint of the neutron star equation of state: gravitational waves via its effect on tidal disruption, the kilonova via its effect on the ejecta, and the gamma ray burst via its effect on the remnant disk. These effects have been studied by numerical simulations and quantified by semi-analytic formulae. However, most of the simulations on which these formulae are based use equations of state without finite temperature and composition-dependent nuclear physics. In this paper, we simulate black hole-neutron star mergers varying both the neutron star mass and the equation of state, using three finite-temperature nuclear models of varying stiffness. Our simulations largely vindicate formulae for ejecta properties but do not find the expected dependence of disk mass on neutron star compaction. We track the early evolution of the accretion disk, largely driven by shocking and fallback inflow, and do find notable equation of state effects on the structure of this early-time, neutrino-bright disk. Comment: 10 pages, 11 figures, submitted to Phys. Rev. D

  • Open Access English
    Authors: 
    Foucart, Francois; Chernoglazov, Alexander; Boyle, Michael; Hinderer, Tanja; Miller, Max; Moxon, Jordan; Scheel, Mark A.; Deppe, Nils; Duez, Matthew D.; Hebert, Francois; +3 more
    Project: NSERC , NSF | Gravitational Radiation a... (1708213), NSF | Simulating the Multi-Mess... (1806278), NSF | Mergers, Stars, and Disks... (1806207), NSF | WoU-MMA: Research in Blac... (1912081), NSF | Elements:Collaborative Pr... (1931280)

    The availability of accurate numerical waveforms is an important requirement for the creation and calibration of reliable waveform models for gravitational wave astrophysics. For black hole-neutron star binaries, very few accurate waveforms are however publicly available. Most recent models are calibrated to a large number of older simulations with good parameter space coverage for low-spin non-precessing binaries but limited accuracy, and a much smaller number of longer, more recent simulations limited to non-spinning black holes. In this paper, we present long, accurate numerical waveforms for three new systems that include rapidly spinning black holes, and one precessing configuration. We study in detail the accuracy of the simulations, and in particular perform for the first time in the context of BHNS binaries a detailed comparison of waveform extrapolation methods to the results of Cauchy Characteristic Extraction. The new waveforms have $0.99$) for binaries seen face-on. For edge-on observations, particularly for precessing systems, disagreements between models and simulations increase, and models that include precession and/or higher-order modes start to perform better than BHNS models that currently lack these features. Comment: 16p, 14 figs, 2 tables; To be submitted to PRD

  • Open Access English
    Authors: 
    Duez, Matthew D.; Knight, Alexander; Foucart, Francois; Haddadi, Milad; Jesse, Jerred; Hebert, Francois; Kidder, Lawrence E.; Pfeiffer, Harald P.; Scheel, Mark A.;
    Project: NSERC , NSF | Gravitational Radiation a... (1708213), NSF | WoU-MMA: Research in Blac... (1912081), NSF | Maximizing Science Output... (1708212), NSF | Simulating the Multi-Mess... (1806278), NSF | Mergers, Stars, and Disks... (1806207)

    The main problems of nonvacuum numerical relativity, compact binary mergers and stellar collapse, involve hydromagnetic instabilities and turbulent flows, so that kinetic energy at small scales have mean effects at large scale that drive the secular evolution. Notable among these effects is momentum transport. We investigate two models of this transport effect, a relativistic Navier-Stokes system and a turbulent mean stress model, that are similar to all of the prescriptions that have been attempted to date for treating subgrid effects on binary neutron star mergers and their aftermath. Our investigation involves both stability analysis and numerical experimentation on star and disk systems. We also begin the investigation of the effects of particle and heat transport on post-merger simulations. We find that correct handling of turbulent heating can be important for avoiding unphysical instabilities. Given such appropriate handling, the evolution of a differentially rotating star and the accretion rate of a disk are reassuringly insensitive to the choice of prescription. However, disk outflows can be sensitive to the choice of method, even for the same effective viscous strength. We also consider the effects of eddy diffusion in the evolution of an accretion disk and show that it can interestingly affect the composition of outflows. Comment: 15 pagers, 11 figures

  • Open Access English
    Authors: 
    Jesse, Jerred; Duez, Matthew D.; Foucart, Francois; Haddadi, Milad; Knight, Alexander L.; Cadenhead, Courtney L.; Hebert, Francois; Kidder, Lawrence E.; Pfeiffer, Harald P.; Scheel, Mark A.;
    Project: NSERC , NSF | Gravitational Radiation a... (1708213), NSF | Simulating the Multi-Mess... (1806278), NSF | WoU-MMA: Research in Blac... (1912081), NSF | Mergers, Stars, and Disks... (1806207)

    We describe a method of implementing the axisymmetric evolution of general-relativistic hydrodynamics and magnetohydrodynamics through modification of a multipatch grid scheme. In order to ease the computational requirements required to evolve the post-merger phase of systems involving binary compact massive objects in numerical relativity, it is often beneficial to take advantage of these system's tendency to rapidly settle into states that are nearly axisymmetric, allowing for 2D evolution of secular timescales. We implement this scheme in the spectral Einstein code and show the results of application of this method to four test systems including viscosity, magnetic fields, and neutrino radiation transport. Our results show that this method can be used to quickly allow already existing 3D infrastructure that makes use of local coordinate system transformations to be made to run in axisymmetric 2D with the flexible grid creation capabilities of multipatch methods. Our code tests include a simple model of a binary neutron star postmerger remnant, for which we confirm the formation of a massive torus which is a promising source of post-merger ejecta. Comment: 33 pages, 11 figures

  • Open Access English
    Authors: 
    Foucart, Francois; Duez, Matthew D.; Gudinas, Alana; Hebert, Francois; Kidder, Lawrence E.; Pfeiffer, Harald P.; Scheel, Mark A.;
    Project: NSERC , NSF | MRI: Aquisition of Comput... (1229408), NSF | Mergers, Stars, and Disks... (1806207), NSF | Simulating the Multi-Mess... (1806278), NSF | Gravitational Radiation a... (1708213), NSF | Sustained-Petascale In Ac... (1238993), NSF | Leadership Class Scientif... (0725070), NSF | WoU-MMA: Research in Blac... (1912081)

    High-accuracy numerical simulations of merging neutron stars play an important role in testing and calibrating the waveform models used by gravitational wave observatories. Obtaining high-accuracy waveforms at a reasonable computational cost, however, remains a significant challenge. One issue is that high-order convergence of the solution requires the use of smooth evolution variables, while many of the equations of state used to model the neutron star matter have discontinuities, typically in the first derivative of the pressure. Spectral formulations of the equation of state have been proposed as a potential solution to this problem. Here, we report on the numerical implementation of spectral equations of state in the Spectral Einstein Code. We show that, in our code, spectral equations of state allow for high-accuracy simulations at a lower computational cost than commonly used `piecewise polytrope' equations state. We also demonstrate that not all spectral equations of state are equally useful: different choices for the low-density part of the equation of state can significantly impact the cost and accuracy of simulations. As a result, simulations of neutron star mergers present us with a trade-off between the cost of simulations and the physical realism of the chosen equation of state. Comment: Submitted to PRD, 13p, 7 figures, 3 tables

  • Open Access
    Authors: 
    Wyatt Brege; Matthew D. Duez; Francois Foucart; M. Brett Deaton; Jesus Caro; Daniel A. Hemberger; Lawrence E. Kidder; Evan O'Connor; Harald P. Pfeiffer; Mark A. Scheel;
    Publisher: American Physical Society (APS)
    Country: United States
    Project: NSF | Gravitational Radiation a... (1708213), NSF | Numerical Simulations of ... (1402916), NSF | MRI-R2: Acquisition of a ... (0960291), NSF | Maximizing Science Output... (1708212), NSF | Mergers, Stars, and Disks... (1806207), NSF | Collaborative Research: P... (1440083), NSF | Gravitational Radiation a... (1404569), NSERC

    Each of the potential signals from a black hole-neutron star merger should contain an imprint of the neutron star equation of state: gravitational waves via its effect on tidal disruption, the kilonova via its effect on the ejecta, and the gamma ray burst via its effect on the remnant disk. These effects have been studied by numerical simulations and quantified by semi-analytic formulae. However, most of the simulations on which these formulae are based use equations of state without finite temperature and composition-dependent nuclear physics. In this paper, we simulate black hole-neutron star mergers varying both the neutron star mass and the equation of state, using three finite-temperature nuclear models of varying stiffness. Our simulations largely vindicate formulae for ejecta properties but do not find the expected dependence of disk mass on neutron star compaction. We track the early evolution of the accretion disk, largely driven by shocking and fallback inflow, and do find notable equation of state effects on the structure of this early-time, neutrino-bright disk. 10 pages, 11 figures, submitted to Phys. Rev. D

  • Open Access
    Authors: 
    Tanja Hinderer; Samaya Nissanke; Francois Foucart; Kenta Hotokezaka; Trevor Vincent; Mansi M. Kasliwal; Patricia Schmidt; A. R. Williamson; David A. Nichols; Matthew D. Duez; +3 more
    Publisher: American Physical Society (APS)
    Countries: United States, Netherlands, Netherlands, Netherlands, Netherlands, United Kingdom
    Project: NSERC , NSF | Maximizing Science Output... (1708212), NSF | Gravitational Radiation a... (1708213), NWO | Precision Gravity: black ... (680-47-460), NSF | Mergers, Stars, and Disks... (1806207), NSF | PIRE: GROWTH: Global Rela... (1545949), NSF | Gravitational Radiation a... (1404569)

    The discovery of GW170817 with gravitational waves (GWs) and electromagnetic (EM) radiation is prompting new questions in strong-gravity astrophysics. Importantly, it remains unknown whether the progenitor of the merger comprised two neutron stars (NSs), or a NS and a black hole (BH). Using new numerical-relativity simulations and incorporating modeling uncertainties we produce novel GW and EM observables for NS-BH mergers with similar masses. A joint analysis of GW and EM measurements reveals that if GW170817 is a NS-BH merger, <40% of the binary parameters consistent with the GW data are compatible with EM observations. 8 pages

  • Open Access English
    Authors: 
    Foucart, Francois; Duez, Matthew D.; Hinderer, Tanja; Caro, Jesus; Williamson, Andrew R.; Boyle, Michael; Buonanno, Alessandra; Haas, Roland; Hemberger, Daniel A.; Kidder, Lawrence E.; +2 more
    Project: NSERC , NSF | Simulating the Multi-Mess... (1806278), NSF | MRI-R2: Acquisition of a ... (0960291), NSF | Mergers, Stars, and Disks... (1806207), NSF | Leadership Class Scientif... (0725070), NSF | Sustained-Petascale In Ac... (1238993), NSF | Inter-agency Workshop for... (1551592), NSF | Gravitational Radiation a... (1708213)

    Gravitational waveforms from numerical simulations are a critical tool to test and analytically calibrate the waveform models used to study the properties of merging compact objects. In this paper, we present a series of high-accuracy waveforms produced with the SpEC code for systems involving at least one neutron star. We provide for the first time waveforms with sub-radian accuracy over more than twenty cycles for low-mass black hole-neutron star binaries, including binaries with non-spinning objects, and binaries with rapidly spinning neutron stars that maximize the impact on the gravitational wave signal of the near-resonant growth of the fundamental excitation mode of the neutron star (f-mode). We also provide for the first time with SpEC a high-accuracy neutron star-neutron star waveform. These waveforms are made publicly available as part of the SxS catalogue. We compare our results to analytical waveform models currently implemented in data analysis pipelines. For most simulations, the models lie outside of the predicted numerical errors in the last few orbits before merger, but do not show systematic deviations from the numerical results: comparing different models appears to provide reasonable estimates of the modeling errors. The sole exception is the equal-mass simulation using a rapidly counter-rotating neutron star to maximize the impact of the excitation of the f-mode, for which all models perform poorly. This is however expected, as even the single model that takes f-mode excitation into account ignores the significant impact of the neutron star spin on the f-mode excitation frequency. Comment: 17p, 10 figures