David Vartanyan - Academia.edu (original) (raw)

Papers by David Vartanyan

Research paper thumbnail of Core-collapse supernova neutrino emission and detection informed by state-of-the-art three-dimensional numerical models

Monthly Notices of the Royal Astronomical Society

Based on our recent three-dimensional core-collapse supernova (CCSN) simulations including both e... more Based on our recent three-dimensional core-collapse supernova (CCSN) simulations including both exploding and non-exploding models, we study the detailed neutrino signals in representative terrestrial neutrino observatories, namely Super-Kamiokande (Hyper-Kamiokande), DUNE, JUNO, and IceCube. We find that the physical origin of difference in the neutrino signals between 1D and 3D is mainly proto-neutron-star convection. We study the temporal and angular variations of the neutrino signals and discuss the detectability of the time variations driven by the spiral standing accretion shock instability (spiral SASI) when it emerges for non-exploding models. In addition, we determine that there can be a large angular asymmetry in the event rate (${\gtrsim} 50 {{\ \rm per\ cent}}$), but the time-integrated signal has a relatively modest asymmetry (${\lesssim} 20 {{\ \rm per\ cent}}$). Both features are associated with the lepton-number emission self-sustained asymmetry and the spiral SASI. ...

Research paper thumbnail of A systematic study of proto-neutron star convection in three-dimensional core-collapse supernova simulations

Monthly Notices of the Royal Astronomical Society

This paper presents the first systematic study of proto-neutron star (PNS) convection in three di... more This paper presents the first systematic study of proto-neutron star (PNS) convection in three dimensions (3D) based on our latest numerical fornax models of core-collapse supernova (CCSN). We confirm that PNS convection commonly occurs, and then quantify the basic physical characteristics of the convection. By virtue of the large number of long-term models, the diversity of PNS convective behaviour emerges. We find that the vigour of PNS convection is not correlated with CCSN dynamics at large radii, but rather with the mass of PNS − heavier masses are associated with stronger PNS convection. We find that PNS convection boosts the luminosities of νμ, ντ, barnumu\bar{\nu }_{\mu }barnumu, and barnutau\bar{\nu }_{\tau }barnutau neutrinos, while the impact on other species is complex due to a competition of factors. Finally, we assess the consequent impact on CCSN dynamics and the potential for PNS convection to generate pulsar magnetic fields.

Research paper thumbnail of The missing link in gravitational-wave astronomy: discoveries waiting in the decihertz range

Classical and Quantum Gravity

Research paper thumbnail of Gravitational Waves from Neutrino Emission Asymmetries in Core-collapse Supernovae

The Astrophysical Journal

Research paper thumbnail of The overarching framework of core-collapse supernova explosions as revealed by 3D fornax simulations

Monthly Notices of the Royal Astronomical Society

We have conducted 19 state-of-the-art 3D core-collapse supernova simulations spanning a broad ran... more We have conducted 19 state-of-the-art 3D core-collapse supernova simulations spanning a broad range of progenitor masses. This is the largest collection of sophisticated 3D supernova simulations ever performed. We have found that while the majority of these models explode, not all do, and that even models in the middle of the available progenitor mass range may be less explodable. This does not mean that those models for which we did not witness explosion would not explode in Nature, but that they are less prone to explosion than others. One consequence is that the ‘compactness’ measure is not a metric for explodability. We find that lower-mass massive star progenitors likely experience lower-energy explosions, while the higher-mass massive stars likely experience higher-energy explosions. Moreover, most 3D explosions have a dominant dipole morphology, have a pinched, wasp-waist structure, and experience simultaneous accretion and explosion. We reproduce the general range of residua...

Research paper thumbnail of Towards an Understanding of the Resolution Dependence of Core-Collapse Supernova Simulations

Monthly Notices of the Royal Astronomical Society

Using our new state-of-the-art core-collapse supernova (CCSN) code F ornax, we explore the depend... more Using our new state-of-the-art core-collapse supernova (CCSN) code F ornax, we explore the dependence upon spatial resolution of the outcome and character of three-dimensional (3D) supernova simulations. For the same 19-M⊙ progenitor star, energy and radial binning, neutrino microphysics, and nuclear equation of state, changing only the number of angular bins in the θ and φ directions, we witness that our lowest resolution 3D simulation does not explode. However, when jumping progressively up in resolution by factors of two in each angular direction on our spherical-polar grid, models then explode, and explode slightly more vigorously with increasing resolution. This suggests that there can be a qualitative dependence of the outcome of 3D CCSN simulations upon spatial resolution. The critical aspect of higher spatial resolution is the adequate capturing of the physics of neutrino-driven turbulence, in particular its Reynolds stress. The greater numerical viscosity of lower-resolutio...

Research paper thumbnail of Detection prospects of core-collapse supernovae with supernova-optimized third-generation gravitational-wave detectors

Physical Review D

We discuss how to optimize the third-generation gravitational-wave detector to maximize the range... more We discuss how to optimize the third-generation gravitational-wave detector to maximize the range to detect core-collapse supernovae. Based on three-dimensional simulations for core-collapse and the corresponding gravitational-wave waveform emitted, the corresponding detection range for these waveforms is limited to within our galaxy even in the era of third-generation detectors. The corresponding event rate is two per century. We find from the waveforms that to detect core-collapse supernovae with an event rate of one per year, the gravitational-wave detectors need a strain sensitivity of 3×10 −27 Hz −1/2 in a frequency range from 100 Hz to 1500 Hz. We also explore detector configurations technologically beyond the scope of third-generation detectors. We find with these improvements, the event rate for gravitational-wave observations from CCSNe is still low, but is improved to one in twenty years.

Research paper thumbnail of Temporal and Angular Variations of 3D Core-Collapse Supernova Emissions and their Physical Correlations

Monthly Notices of the Royal Astronomical Society

We provide the time series and angular distributions of the neutrino and gravitational-wave emiss... more We provide the time series and angular distributions of the neutrino and gravitational-wave emissions of eleven state-of-the-art three-dimensional non-rotating core-collapse supernova models and explore correlations between these signatures and the real-time dynamics of the shock and the proto-neutron-star core. The neutrino emissions are roughly isotropic on average, with instantaneous excursions about the mean inferred luminosity of as much as ±20%. The deviation from isotropy is least for the “νμ”-type neutrinos and the lowest-mass progenitors. Instantaneous temporal luminosity variations along a given direction for exploding models average ∼2 −4%, but can be as high as ∼10%. For non-exploding models, they can achieve ∼25%. The temporal variations in the neutrino emissions correlate with the temporal and angular variations in the mass accretion rate. We witness the LESA phenomenon in all our models and find that the vector direction of the LESA dipole and that of the inner Ye dis...

Research paper thumbnail of Characterizing the Gravitational Wave Signal from Core-collapse Supernovae

The Astrophysical Journal

We study the gravitational wave signal from eight new 3D core-collapse supernova simulations. We ... more We study the gravitational wave signal from eight new 3D core-collapse supernova simulations. We show that the signal is dominated by f-and g-mode oscillations of the protoneutron star and its frequency evolution encodes the contraction rate of the latter, which, in turn, is known to depend on the star's mass, on the equation of state, and on transport properties in warm nuclear matter. A lower-frequency component of the signal, associated with the standing accretion shock instability, is found in only one of our models. Finally, we show that the energy radiated in gravitational waves is proportional to the amount of turbulent energy accreted by the protoneutron star.

Research paper thumbnail of Fornax: A Flexible Code for Multiphysics Astrophysical Simulations

The Astrophysical Journal Supplement Series

This paper describes the design and implementation of our new multigroup, multidimensional radiat... more This paper describes the design and implementation of our new multigroup, multidimensional radiation hydrodynamics code FORNAX and provides a suite of code tests to validate its application in a wide range of physical regimes. Instead of focusing exclusively on tests of neutrino radiation hydrodynamics relevant to the corecollapse supernova problem for which FORNAX is primarily intended, we present here classical and rigorous demonstrations of code performance relevant to a broad range of multidimensional hydrodynamic and multigroup radiation hydrodynamic problems. Our code solves the comoving-frame radiation moment equations using the M1 closure, utilizes conservative high-order reconstruction, employs semi-explicit matter and radiation transport via a high-order time stepping scheme, and is suitable for application to a wide range of astrophysical problems. To this end, we first describe the philosophy, algorithms, and methodologies of FORNAX and then perform numerous stringent code tests that collectively and vigorously exercise the code, demonstrate the excellent numerical fidelity with which it captures the many physical effects of radiation hydrodynamics, and show excellent strong scaling well above 100,000 MPI tasks.

Research paper thumbnail of Neutrino signals of core-collapse supernovae in underground detectors

Monthly Notices of the Royal Astronomical Society

For a suite of 14 core-collapse models during the dynamical first second after bounce, we calcula... more For a suite of 14 core-collapse models during the dynamical first second after bounce, we calculate the detailed neutrino 'light' curves expected in the underground neutrino observatories Super-Kamiokande, DUNE, JUNO, and IceCube. These results are given as a function of neutrino-oscillation modality (normal or inverted hierarchy) and progenitor mass (specifically, post-bounce accretion history), and illuminate the differences between the light curves for 1D (spherical) models that don't explode with the corresponding 2D (axisymmetric) models that do. We are able to identify clear signatures of explosion (or non-explosion), the post-bounce accretion phase, and the accretion of the silicon/oxygen interface. In addition, we are able to estimate the supernova detection ranges for various physical diagnostics and the distances out to which various temporal features embedded in the light curves might be discerned. We find that the progenitor mass density profile and supernova dynamics during the dynamical explosion stage should be identifiable for a supernova throughout most of the Galaxy in all the facilities studied and that detection by any one of them, but in particular more than one in concert, will speak volumes about the internal dynamics of supernovae.

Research paper thumbnail of A successful 3D core-collapse supernova explosion model

Monthly Notices of the Royal Astronomical Society

In this paper, we present the results of our three-dimensional, multigroup, multineutrinospecies ... more In this paper, we present the results of our three-dimensional, multigroup, multineutrinospecies radiation/hydrodynamic simulation using the state-of-the-art code FORNAX of the terminal dynamics of the core of a non-rotating 16 M stellar progenitor. The calculation incorporates redistribution by inelastic scattering, a correction for the effect of many-body interactions on the neutrino-nucleon scattering rates, approximate general relativity (including the effects of gravitational redshifts), velocity-dependent frequency advection, and an implementation of initial perturbations in the progenitor core. The model explodes within ∼100 ms of bounce (near when the silicon-oxygen interface is accreted through the temporarily stalled shock) and by the end of the simulation (here, ∼677 ms after bounce) is accumulating explosion energy at a rate of ∼2.5 × 10 50 erg s −1. The supernova explodes with an asymmetrical multiplume structure, with one hemisphere predominating. The gravitational mass of the residual proto-neutron star at ∼677 ms is ∼1.42 M. Even at the end of the simulation, explosion in most of the solid angle is accompanied by some accretion in an annular region at the wasp-like waist of the debris field. The ejecta electron fraction (Y e) is distributed between ∼0.48 and ∼0.56, with most of the ejecta mass proton-rich. This may have implications for supernova nucleosynthesis, and could have a bearing on the p-and νp-processes and on the site of the first peak of the r-process. The ejecta spatial distributions of both Y e and mass density are predominantly in wide-angle plumes and large-scale structures, but are nevertheless quite patchy.

Research paper thumbnail of Global comparison of core-collapse supernova simulations in spherical symmetry

Journal of Physics G: Nuclear and Particle Physics

We present a comparison between several simulation codes designed to study the core-collapse supe... more We present a comparison between several simulation codes designed to study the core-collapse supernova mechanism. We pay close attention to controlling the initial conditions and input physics in order to ensure a meaningful and informative comparison. Our goal is threefold. First, we aim to demonstrate the current level of agreement between various groups studying the corecollapse supernova central engine. Second, we desire to form a strong basis for future simulation codes and methods to compare to. Lastly, we want this work to be a stepping stone for future work exploring more complex simulations of core-collapse supernovae, i.e., simulations in multiple dimensions and simulations with modern neutrino and nuclear physics. We compare the early (first ∼500 ms after core bounce) spherically-symmetric evolution of a 20 M e progenitor star from six different core-collapse supernovae codes: 3DnSNe-IDSA, AGILE-BOLTZTRAN, FLASH, FORNAX, GR1D, and PRO-METHEUS-VERTEX. Given the diversity of neutrino transport and hydrodynamic methods employed, we find excellent agreement in many critical quantities, including the shock radius evolution and the amount of neutrino heating. Our results provide an excellent starting point from which to extend this comparison to higher dimensions and compare the development of hydrodynamic instabilities that are crucial to the supernova explosion mechanism, such as turbulence and convection.

Research paper thumbnail of The Gravitational Wave Signal from Core-collapse Supernovae

The Astrophysical Journal

We study gravitational waves (GWs) from a set of two-dimensional multi-group neutrino radiation h... more We study gravitational waves (GWs) from a set of two-dimensional multi-group neutrino radiation hydrodynamic simulations of core-collapse supernovae (CCSNe). Our goal is to systematize the current knowledge about the post-bounce CCSN GW signal and recognize the templatable features that could be used by the ground-based laser interferometers. We demonstrate that starting from ∼400 ms after core bounce the dominant GW signal represents the fundamental quadrupole (l = 2) oscillation mode (f-mode) of the proto-neutron star (PNS), which can be accurately reproduced by a linear perturbation analysis of the angle-averaged PNS profile. Before that, in the time interval between ∼200 and ∼400 ms after bounce, the dominant mode has two radial nodes and represents a g-mode. We associate the high-frequency noise in the GW spectrograms above the main signal with p-modes, while below the dominant frequency there is a region with very little power. The collection of models presented here summarizes the dependence of the CCSN GW signal on the progenitor mass, equation of state, many-body corrections to the neutrino opacity, and rotation. Weak dependence of the dominant GW frequency on the progenitor mass motivates us to provide a simple fit for it as a function of time, which can be used as a prior when looking for CCSN candidates in the LIGO data.

Research paper thumbnail of Electron-capture and Low-mass Iron-core-collapse Supernovae: New Neutrino-radiation-hydrodynamics Simulations

The Astrophysical Journal

Research paper thumbnail of Tatooine Nurseries: Structure and Evolution of Circumbinary Protoplanetary Disks

The Astrophysical Journal, 2016

Recent discoveries of circumbinary planets by Kepler mission provide motivation for understanding... more Recent discoveries of circumbinary planets by Kepler mission provide motivation for understanding their birthplaces-protoplanetary disks around stellar binaries with separations 1 AU. We explore properties and evolution of such circumbinary disks focusing on modification of their structure caused by tidal coupling to the binary. We develop a set of analytical scaling relations describing viscous evolution of the disk properties, which are verified and calibrated using 1D numerical calculations with realistic inputs. Injection of angular momentum by the central binary suppresses mass accretion onto the binary and causes radial distribution of the viscous angular momentum flux F J to be different from that in a standard accretion disk around a single star with no torque at the center. Disks with no mass accretion at the center develop F J profile which is flat in radius. Radial profiles of temperature and surface density are also quite different from those in disks around single stars. Damping of the density waves driven by the binary and viscous dissipation dominate heating of the inner disk (within 1-2 AU), pushing the iceline beyond 3-5 AU, depending on disk mass and age. Irradiation by the binary governs disk thermodynamics beyond ∼ 10 AU. However, self-shadowing by the hot inner disk may render central illumination irrelevant out to ∼ 20 AU. Spectral energy distribution of a circumbinary disk exhibits a distinctive bump around 10µm, which may facilitate identification of such disks around unresolved binaries. Efficient tidal coupling to the disk drives orbital inspiral of the binary and may cause low-mass and relatively compact binaries to merge into a single star within the disk lifetime. We generally find that circumbinary disks present favorable sites for planet formation (despite their wider zone of volatile depletion), in agreement with the statistics of Kepler circumbinary planets. Subject headings: planets and satellites: formation-protoplanetary disks-stars: planetary systems 1. INTRODUCTION.

Research paper thumbnail of Revival of the fittest: exploding core-collapse supernovae from 12 to 25 M⊙

Monthly Notices of the Royal Astronomical Society

We present results of 2D axisymmetric core-collapse supernova simulations, employing the FORNAX c... more We present results of 2D axisymmetric core-collapse supernova simulations, employing the FORNAX code, of nine progenitor models spanning 12 to 25 M. Four of the models explode with inelastic scattering off electrons and neutrons as well as the many-body correction to neutrino-nucleon scattering opacities. We show that these four models feature sharp Si-O interfaces in their density profiles, and that the corresponding dip in density reduces the accretion rate around the stalled shock and prompts explosion. The non-exploding models lack such a steep feature, highlighting the Si-O interface as one key to explosion. Furthermore, we show that all of the non-exploding models can be nudged to explosion with modest changes to macrophysical inputs, including moderate rotation and perturbations to infall velocities, as well as to microphysical inputs, including reasonable changes to neutrino-nucleon interaction rates, suggesting that all the models are perhaps close to criticality. Exploding models have energies of a few × 10 50 erg at the end of our simulation, and are rising, emphasizing the need to continue these simulations over larger grids and for longer times to reproduce the energies seen in nature. Morphology of the explosion contributes to the explosion energy, with more isotropic ejecta producing larger explosion energies. We do not find evidence for the Lepton-number Emission Self-sustained Asymmetry. Finally, we look at proto-neutron star (PNS) properties and explore the role of dimension in our simulations. We find that convection in the PNS produces larger PNS radii as well as greater 'ν μ ' luminosities in 2D compared to 1D.

Research paper thumbnail of Core-collapse supernova neutrino emission and detection informed by state-of-the-art three-dimensional numerical models

Monthly Notices of the Royal Astronomical Society

Based on our recent three-dimensional core-collapse supernova (CCSN) simulations including both e... more Based on our recent three-dimensional core-collapse supernova (CCSN) simulations including both exploding and non-exploding models, we study the detailed neutrino signals in representative terrestrial neutrino observatories, namely Super-Kamiokande (Hyper-Kamiokande), DUNE, JUNO, and IceCube. We find that the physical origin of difference in the neutrino signals between 1D and 3D is mainly proto-neutron-star convection. We study the temporal and angular variations of the neutrino signals and discuss the detectability of the time variations driven by the spiral standing accretion shock instability (spiral SASI) when it emerges for non-exploding models. In addition, we determine that there can be a large angular asymmetry in the event rate (${\gtrsim} 50 {{\ \rm per\ cent}}$), but the time-integrated signal has a relatively modest asymmetry (${\lesssim} 20 {{\ \rm per\ cent}}$). Both features are associated with the lepton-number emission self-sustained asymmetry and the spiral SASI. ...

Research paper thumbnail of A systematic study of proto-neutron star convection in three-dimensional core-collapse supernova simulations

Monthly Notices of the Royal Astronomical Society

This paper presents the first systematic study of proto-neutron star (PNS) convection in three di... more This paper presents the first systematic study of proto-neutron star (PNS) convection in three dimensions (3D) based on our latest numerical fornax models of core-collapse supernova (CCSN). We confirm that PNS convection commonly occurs, and then quantify the basic physical characteristics of the convection. By virtue of the large number of long-term models, the diversity of PNS convective behaviour emerges. We find that the vigour of PNS convection is not correlated with CCSN dynamics at large radii, but rather with the mass of PNS − heavier masses are associated with stronger PNS convection. We find that PNS convection boosts the luminosities of νμ, ντ, barnumu\bar{\nu }_{\mu }barnumu, and barnutau\bar{\nu }_{\tau }barnutau neutrinos, while the impact on other species is complex due to a competition of factors. Finally, we assess the consequent impact on CCSN dynamics and the potential for PNS convection to generate pulsar magnetic fields.

Research paper thumbnail of The missing link in gravitational-wave astronomy: discoveries waiting in the decihertz range

Classical and Quantum Gravity

Research paper thumbnail of Gravitational Waves from Neutrino Emission Asymmetries in Core-collapse Supernovae

The Astrophysical Journal

Research paper thumbnail of The overarching framework of core-collapse supernova explosions as revealed by 3D fornax simulations

Monthly Notices of the Royal Astronomical Society

We have conducted 19 state-of-the-art 3D core-collapse supernova simulations spanning a broad ran... more We have conducted 19 state-of-the-art 3D core-collapse supernova simulations spanning a broad range of progenitor masses. This is the largest collection of sophisticated 3D supernova simulations ever performed. We have found that while the majority of these models explode, not all do, and that even models in the middle of the available progenitor mass range may be less explodable. This does not mean that those models for which we did not witness explosion would not explode in Nature, but that they are less prone to explosion than others. One consequence is that the ‘compactness’ measure is not a metric for explodability. We find that lower-mass massive star progenitors likely experience lower-energy explosions, while the higher-mass massive stars likely experience higher-energy explosions. Moreover, most 3D explosions have a dominant dipole morphology, have a pinched, wasp-waist structure, and experience simultaneous accretion and explosion. We reproduce the general range of residua...

Research paper thumbnail of Towards an Understanding of the Resolution Dependence of Core-Collapse Supernova Simulations

Monthly Notices of the Royal Astronomical Society

Using our new state-of-the-art core-collapse supernova (CCSN) code F ornax, we explore the depend... more Using our new state-of-the-art core-collapse supernova (CCSN) code F ornax, we explore the dependence upon spatial resolution of the outcome and character of three-dimensional (3D) supernova simulations. For the same 19-M⊙ progenitor star, energy and radial binning, neutrino microphysics, and nuclear equation of state, changing only the number of angular bins in the θ and φ directions, we witness that our lowest resolution 3D simulation does not explode. However, when jumping progressively up in resolution by factors of two in each angular direction on our spherical-polar grid, models then explode, and explode slightly more vigorously with increasing resolution. This suggests that there can be a qualitative dependence of the outcome of 3D CCSN simulations upon spatial resolution. The critical aspect of higher spatial resolution is the adequate capturing of the physics of neutrino-driven turbulence, in particular its Reynolds stress. The greater numerical viscosity of lower-resolutio...

Research paper thumbnail of Detection prospects of core-collapse supernovae with supernova-optimized third-generation gravitational-wave detectors

Physical Review D

We discuss how to optimize the third-generation gravitational-wave detector to maximize the range... more We discuss how to optimize the third-generation gravitational-wave detector to maximize the range to detect core-collapse supernovae. Based on three-dimensional simulations for core-collapse and the corresponding gravitational-wave waveform emitted, the corresponding detection range for these waveforms is limited to within our galaxy even in the era of third-generation detectors. The corresponding event rate is two per century. We find from the waveforms that to detect core-collapse supernovae with an event rate of one per year, the gravitational-wave detectors need a strain sensitivity of 3×10 −27 Hz −1/2 in a frequency range from 100 Hz to 1500 Hz. We also explore detector configurations technologically beyond the scope of third-generation detectors. We find with these improvements, the event rate for gravitational-wave observations from CCSNe is still low, but is improved to one in twenty years.

Research paper thumbnail of Temporal and Angular Variations of 3D Core-Collapse Supernova Emissions and their Physical Correlations

Monthly Notices of the Royal Astronomical Society

We provide the time series and angular distributions of the neutrino and gravitational-wave emiss... more We provide the time series and angular distributions of the neutrino and gravitational-wave emissions of eleven state-of-the-art three-dimensional non-rotating core-collapse supernova models and explore correlations between these signatures and the real-time dynamics of the shock and the proto-neutron-star core. The neutrino emissions are roughly isotropic on average, with instantaneous excursions about the mean inferred luminosity of as much as ±20%. The deviation from isotropy is least for the “νμ”-type neutrinos and the lowest-mass progenitors. Instantaneous temporal luminosity variations along a given direction for exploding models average ∼2 −4%, but can be as high as ∼10%. For non-exploding models, they can achieve ∼25%. The temporal variations in the neutrino emissions correlate with the temporal and angular variations in the mass accretion rate. We witness the LESA phenomenon in all our models and find that the vector direction of the LESA dipole and that of the inner Ye dis...

Research paper thumbnail of Characterizing the Gravitational Wave Signal from Core-collapse Supernovae

The Astrophysical Journal

We study the gravitational wave signal from eight new 3D core-collapse supernova simulations. We ... more We study the gravitational wave signal from eight new 3D core-collapse supernova simulations. We show that the signal is dominated by f-and g-mode oscillations of the protoneutron star and its frequency evolution encodes the contraction rate of the latter, which, in turn, is known to depend on the star's mass, on the equation of state, and on transport properties in warm nuclear matter. A lower-frequency component of the signal, associated with the standing accretion shock instability, is found in only one of our models. Finally, we show that the energy radiated in gravitational waves is proportional to the amount of turbulent energy accreted by the protoneutron star.

Research paper thumbnail of Fornax: A Flexible Code for Multiphysics Astrophysical Simulations

The Astrophysical Journal Supplement Series

This paper describes the design and implementation of our new multigroup, multidimensional radiat... more This paper describes the design and implementation of our new multigroup, multidimensional radiation hydrodynamics code FORNAX and provides a suite of code tests to validate its application in a wide range of physical regimes. Instead of focusing exclusively on tests of neutrino radiation hydrodynamics relevant to the corecollapse supernova problem for which FORNAX is primarily intended, we present here classical and rigorous demonstrations of code performance relevant to a broad range of multidimensional hydrodynamic and multigroup radiation hydrodynamic problems. Our code solves the comoving-frame radiation moment equations using the M1 closure, utilizes conservative high-order reconstruction, employs semi-explicit matter and radiation transport via a high-order time stepping scheme, and is suitable for application to a wide range of astrophysical problems. To this end, we first describe the philosophy, algorithms, and methodologies of FORNAX and then perform numerous stringent code tests that collectively and vigorously exercise the code, demonstrate the excellent numerical fidelity with which it captures the many physical effects of radiation hydrodynamics, and show excellent strong scaling well above 100,000 MPI tasks.

Research paper thumbnail of Neutrino signals of core-collapse supernovae in underground detectors

Monthly Notices of the Royal Astronomical Society

For a suite of 14 core-collapse models during the dynamical first second after bounce, we calcula... more For a suite of 14 core-collapse models during the dynamical first second after bounce, we calculate the detailed neutrino 'light' curves expected in the underground neutrino observatories Super-Kamiokande, DUNE, JUNO, and IceCube. These results are given as a function of neutrino-oscillation modality (normal or inverted hierarchy) and progenitor mass (specifically, post-bounce accretion history), and illuminate the differences between the light curves for 1D (spherical) models that don't explode with the corresponding 2D (axisymmetric) models that do. We are able to identify clear signatures of explosion (or non-explosion), the post-bounce accretion phase, and the accretion of the silicon/oxygen interface. In addition, we are able to estimate the supernova detection ranges for various physical diagnostics and the distances out to which various temporal features embedded in the light curves might be discerned. We find that the progenitor mass density profile and supernova dynamics during the dynamical explosion stage should be identifiable for a supernova throughout most of the Galaxy in all the facilities studied and that detection by any one of them, but in particular more than one in concert, will speak volumes about the internal dynamics of supernovae.

Research paper thumbnail of A successful 3D core-collapse supernova explosion model

Monthly Notices of the Royal Astronomical Society

In this paper, we present the results of our three-dimensional, multigroup, multineutrinospecies ... more In this paper, we present the results of our three-dimensional, multigroup, multineutrinospecies radiation/hydrodynamic simulation using the state-of-the-art code FORNAX of the terminal dynamics of the core of a non-rotating 16 M stellar progenitor. The calculation incorporates redistribution by inelastic scattering, a correction for the effect of many-body interactions on the neutrino-nucleon scattering rates, approximate general relativity (including the effects of gravitational redshifts), velocity-dependent frequency advection, and an implementation of initial perturbations in the progenitor core. The model explodes within ∼100 ms of bounce (near when the silicon-oxygen interface is accreted through the temporarily stalled shock) and by the end of the simulation (here, ∼677 ms after bounce) is accumulating explosion energy at a rate of ∼2.5 × 10 50 erg s −1. The supernova explodes with an asymmetrical multiplume structure, with one hemisphere predominating. The gravitational mass of the residual proto-neutron star at ∼677 ms is ∼1.42 M. Even at the end of the simulation, explosion in most of the solid angle is accompanied by some accretion in an annular region at the wasp-like waist of the debris field. The ejecta electron fraction (Y e) is distributed between ∼0.48 and ∼0.56, with most of the ejecta mass proton-rich. This may have implications for supernova nucleosynthesis, and could have a bearing on the p-and νp-processes and on the site of the first peak of the r-process. The ejecta spatial distributions of both Y e and mass density are predominantly in wide-angle plumes and large-scale structures, but are nevertheless quite patchy.

Research paper thumbnail of Global comparison of core-collapse supernova simulations in spherical symmetry

Journal of Physics G: Nuclear and Particle Physics

We present a comparison between several simulation codes designed to study the core-collapse supe... more We present a comparison between several simulation codes designed to study the core-collapse supernova mechanism. We pay close attention to controlling the initial conditions and input physics in order to ensure a meaningful and informative comparison. Our goal is threefold. First, we aim to demonstrate the current level of agreement between various groups studying the corecollapse supernova central engine. Second, we desire to form a strong basis for future simulation codes and methods to compare to. Lastly, we want this work to be a stepping stone for future work exploring more complex simulations of core-collapse supernovae, i.e., simulations in multiple dimensions and simulations with modern neutrino and nuclear physics. We compare the early (first ∼500 ms after core bounce) spherically-symmetric evolution of a 20 M e progenitor star from six different core-collapse supernovae codes: 3DnSNe-IDSA, AGILE-BOLTZTRAN, FLASH, FORNAX, GR1D, and PRO-METHEUS-VERTEX. Given the diversity of neutrino transport and hydrodynamic methods employed, we find excellent agreement in many critical quantities, including the shock radius evolution and the amount of neutrino heating. Our results provide an excellent starting point from which to extend this comparison to higher dimensions and compare the development of hydrodynamic instabilities that are crucial to the supernova explosion mechanism, such as turbulence and convection.

Research paper thumbnail of The Gravitational Wave Signal from Core-collapse Supernovae

The Astrophysical Journal

We study gravitational waves (GWs) from a set of two-dimensional multi-group neutrino radiation h... more We study gravitational waves (GWs) from a set of two-dimensional multi-group neutrino radiation hydrodynamic simulations of core-collapse supernovae (CCSNe). Our goal is to systematize the current knowledge about the post-bounce CCSN GW signal and recognize the templatable features that could be used by the ground-based laser interferometers. We demonstrate that starting from ∼400 ms after core bounce the dominant GW signal represents the fundamental quadrupole (l = 2) oscillation mode (f-mode) of the proto-neutron star (PNS), which can be accurately reproduced by a linear perturbation analysis of the angle-averaged PNS profile. Before that, in the time interval between ∼200 and ∼400 ms after bounce, the dominant mode has two radial nodes and represents a g-mode. We associate the high-frequency noise in the GW spectrograms above the main signal with p-modes, while below the dominant frequency there is a region with very little power. The collection of models presented here summarizes the dependence of the CCSN GW signal on the progenitor mass, equation of state, many-body corrections to the neutrino opacity, and rotation. Weak dependence of the dominant GW frequency on the progenitor mass motivates us to provide a simple fit for it as a function of time, which can be used as a prior when looking for CCSN candidates in the LIGO data.

Research paper thumbnail of Electron-capture and Low-mass Iron-core-collapse Supernovae: New Neutrino-radiation-hydrodynamics Simulations

The Astrophysical Journal

Research paper thumbnail of Tatooine Nurseries: Structure and Evolution of Circumbinary Protoplanetary Disks

The Astrophysical Journal, 2016

Recent discoveries of circumbinary planets by Kepler mission provide motivation for understanding... more Recent discoveries of circumbinary planets by Kepler mission provide motivation for understanding their birthplaces-protoplanetary disks around stellar binaries with separations 1 AU. We explore properties and evolution of such circumbinary disks focusing on modification of their structure caused by tidal coupling to the binary. We develop a set of analytical scaling relations describing viscous evolution of the disk properties, which are verified and calibrated using 1D numerical calculations with realistic inputs. Injection of angular momentum by the central binary suppresses mass accretion onto the binary and causes radial distribution of the viscous angular momentum flux F J to be different from that in a standard accretion disk around a single star with no torque at the center. Disks with no mass accretion at the center develop F J profile which is flat in radius. Radial profiles of temperature and surface density are also quite different from those in disks around single stars. Damping of the density waves driven by the binary and viscous dissipation dominate heating of the inner disk (within 1-2 AU), pushing the iceline beyond 3-5 AU, depending on disk mass and age. Irradiation by the binary governs disk thermodynamics beyond ∼ 10 AU. However, self-shadowing by the hot inner disk may render central illumination irrelevant out to ∼ 20 AU. Spectral energy distribution of a circumbinary disk exhibits a distinctive bump around 10µm, which may facilitate identification of such disks around unresolved binaries. Efficient tidal coupling to the disk drives orbital inspiral of the binary and may cause low-mass and relatively compact binaries to merge into a single star within the disk lifetime. We generally find that circumbinary disks present favorable sites for planet formation (despite their wider zone of volatile depletion), in agreement with the statistics of Kepler circumbinary planets. Subject headings: planets and satellites: formation-protoplanetary disks-stars: planetary systems 1. INTRODUCTION.

Research paper thumbnail of Revival of the fittest: exploding core-collapse supernovae from 12 to 25 M⊙

Monthly Notices of the Royal Astronomical Society

We present results of 2D axisymmetric core-collapse supernova simulations, employing the FORNAX c... more We present results of 2D axisymmetric core-collapse supernova simulations, employing the FORNAX code, of nine progenitor models spanning 12 to 25 M. Four of the models explode with inelastic scattering off electrons and neutrons as well as the many-body correction to neutrino-nucleon scattering opacities. We show that these four models feature sharp Si-O interfaces in their density profiles, and that the corresponding dip in density reduces the accretion rate around the stalled shock and prompts explosion. The non-exploding models lack such a steep feature, highlighting the Si-O interface as one key to explosion. Furthermore, we show that all of the non-exploding models can be nudged to explosion with modest changes to macrophysical inputs, including moderate rotation and perturbations to infall velocities, as well as to microphysical inputs, including reasonable changes to neutrino-nucleon interaction rates, suggesting that all the models are perhaps close to criticality. Exploding models have energies of a few × 10 50 erg at the end of our simulation, and are rising, emphasizing the need to continue these simulations over larger grids and for longer times to reproduce the energies seen in nature. Morphology of the explosion contributes to the explosion energy, with more isotropic ejecta producing larger explosion energies. We do not find evidence for the Lepton-number Emission Self-sustained Asymmetry. Finally, we look at proto-neutron star (PNS) properties and explore the role of dimension in our simulations. We find that convection in the PNS produces larger PNS radii as well as greater 'ν μ ' luminosities in 2D compared to 1D.