[Show abstract][Hide abstract] ABSTRACT: We present a new multi-dimensional radiation-hydrodynamics code for massive
stellar core-collapse in full general relativity (GR). Employing an M1
analytical closure scheme, we solve spectral neutrino transport of the
radiation energy and momentum based on a truncated moment formalism. Regarding
neutrino opacities, we take into account the so-called standard set in
state-of-the-art simulations, in which inelastic neutrino-electron scattering,
thermal neutrino production via pair annihilation and nucleon-nucleon
bremsstrahlung are included. In addition to gravitational redshift and Doppler
effects, these energy-coupling reactions are incorporated in the moment
equations in a covariant form. While the Einstein field equations and the
spatial advection terms in the radiation-hydrodynamics equations are evolved
explicitly, the source terms due to neutrino-matter interactions and energy
shift in the radiation moment equations are integrated implicitly by an
iteration method. To verify our code, we conduct several test simulations of
core-collapse, bounce, and shock-stall of a 15 solar mass star in the Cartesian
coordinates and make a detailed comparison with published results. We first
investigate how accurate the adopted closure scheme reproduces results from
spherically-symmetric simulations with full-Boltzmann neutrino transport. A
good agreement of the hydrodynamic features and the spectral neutrino
properties supports the reliability of the GR transport scheme in the momentum
space. These results demonstrate the robustness of our code that is intended to
model core-collapse supernovae. For the actual application, we discuss that
higher numerical resolutions in both space and momentum-space are needed, which
could be possibly practicable by using next-generation Exaflops-class
supercomputers.
[Show abstract][Hide abstract] ABSTRACT: Using predictions from three-dimensional (3D) hydrodynamics simulations of
core-collapse supernovae (CCSNe), we present a coherent network analysis to
detection, reconstruction, and the source localization of the
gravitational-wave (GW) signals. By combining with the GW spectrogram analysis,
we show that several important hydrodynamics features imprinted in the original
waveforms persist in the waveforms of the reconstructed signals. The
characteristic excess in the GW spectrograms originates not only from rotating
core-collapse and bounce, the subsequent ring down of the proto-neutron star
(PNS) as previously identified, but also from the formation of
magnetohydrodynamics jets and non-axisymmetric instabilities in the vicinity of
the PNS. Regarding the GW signals emitted near at the rotating core bounce, the
horizon distance, which we set by a SNR exceeding 8, extends up to $\sim$ 18
kpc for the most rapidly rotating 3D model among the employed waveform
libraries. Following the rotating core bounce, the dominant source of the GW
emission transits to the non-axisymmetric instabilities that develop in the
region between the stalled shock and the PNS. We point out that the horizon
distances from the non-axisymmetric instabilities are generally longer when
seen from the direction parallel to the rotational axis of the source than seen
from the equator. Among the 3D general-relativistic models in which the
non-axisymmetric instabilities set in, the horizon distances extend maximally
up to $\sim$ 40 kpc seen from the pole and they are rather insensitive to the
imposed initial rotation rates. Our results suggest that in addition to the
best studied GW signals due to rotating core-collapse and bounce, the
quasi-periodic signals due to the non-axisymmetric instabilities and the
detectability should deserve further investigation to elucidate the
inner-working of the rapidly rotating CCSNe.
[Show abstract][Hide abstract] ABSTRACT: Magnetorotational instability (MRI) in a convectively-stable layer around the
neutrinosphere is simulated by a three-dimensional model of supernova core. To
resolve MRI-unstable modes, a thin layer approximation considering only the
radial global stratification is adopted. Our intriguing finding is that the
convectively-stable layer around the neutrinosphere becomes fully-turbulent due
to the MRI and its nonlinear penetration into the strongly-stratified
MRI-stable region. The intensity of the MRI-driven turbulence increases with
magnetic flux threading the core, but is limited by a free energy stored in the
differential rotation. The turbulent neutrinosphere is a natural consequence of
rotating core-collapse and could exert a positive impact on the supernova
mechanism.
[Show abstract][Hide abstract] ABSTRACT: Mapping supernovae to their progenitors is fundamental to understanding the collapse of massive stars. We investigate the
red supergiant problem, which concerns why red supergiants with masses ∼16–30 M⊙ have not been identified as progenitors of Type IIP supernovae, and the supernova rate problem, which concerns why the observed
cosmic supernova rate is smaller than the observed cosmic star formation rate. We find key physics to solving these in the
compactness parameter, which characterizes the density structure of the progenitor. If massive stars with compactness above
ξ2.5 ∼ 0.2 fail to produce canonical supernovae, (i) stars in the mass range 16–30 M⊙ populate an island of stars that have high ξ2.5 and do not produce canonical supernovae, and (ii) the fraction of such stars is consistent with the missing fraction of supernovae
relative to star formation. We support this scenario with a series of two- and three-dimensional radiation hydrodynamics core-collapse
simulations. Using more than 300 progenitors covering initial masses 10.8–75 M⊙ and three initial metallicities, we show that high compactness is conducive to failed explosions. We then argue that a critical
compactness of ∼0.2 as the divide between successful and failed explosions is consistent with state-of-the-art three-dimensional
core-collapse simulations. Our study implies that numerical simulations of core collapse need not produce robust explosions
in a significant fraction of compact massive star initial conditions.
Monthly Notices of the Royal Astronomical Society Letters 08/2014; 445(1). DOI:10.1093/mnrasl/slu146 · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: By performing neutrino-radiation hydrodynamic simulations in spherical
symmetry (1D) and axial symmetry (2D) with different progenitor models by
Woosley & Heger (2007) from 12 $M_\odot$ to 100 $M_\odot$, we find that all 1D
runs fail to produce explosion and several 2D runs succeed. The difference of
shock evolution can be interpreted by the difference of mass accretion history,
which is determined by the density structure of the progenitor. The exploding
models exhibit high neutrino luminosity with low mass accretion rate. This is
consistent with the discussion about the so-called critical curve in the mass
accretion rate and neutrino luminosity plane, above which there is no steady
solution of the accretion flow so that a dynamical expanding shock wave is
expected. In addition, we developed a phenomenological model to evaluate the
trajectories in this plane. This model reasonably reproduces the numerical
results by using the initial density structure of the progenitors alone. By
this model, we can predict the possibility of explosion by using the initial
density structure of the progenitors alone.
[Show abstract][Hide abstract] ABSTRACT: We present an overview of axisymmetric core-collapse supernova simulations
employing neutrino transport scheme by the isotropic diffusion source
approximation. Studying 101 solar-metallicity progenitors covering zero-age
main sequence mass from 10.8 to 75.0 solar masses, we systematically
investigate how the differences in the structures of these multiple progenitors
impact the hydrodynamics evolution. By following a long-term evolution over 1.0
s after bounce, most of the computed models exhibit neutrino-driven revival of
the stalled bounce shock at about 200 - 800 ms postbounce, leading to the
possibility of explosion. Pushing the boundaries of expectations in previous
one-dimensional studies, our results show that the time of shock revival,
evolution of shock radii, and diagnostic explosion energies are tightly
correlated with the compactness parameter xi which characterizes the structure
of the progenitors. Compared to models with low xi, models with high xi undergo
high ram pressure from the accreting matter onto the stalled shock and it takes
longer time before the shock expansion is initiated under the influence of
neutrino-driven convection and the standing accretion-shock instability. We
find that the accretion luminosity becomes higher for models with high xi,
which makes the diagnostic energy higher and the synthesized nickel mass
bigger. We point out that these explosion characteristics tend to show a
monotonic increase as a function of the compactness parameter xi.
[Show abstract][Hide abstract] ABSTRACT: We examine the synthesis of 44Ti in a neutrino-driven aspherical supernova (SN), focusing on reaction rates related to 44Ti and rotation of a progenitor. We have performed 2D hydrodynamic simulations of SN of a 15M☉ progenitor, whose angular velocity is manually set to be a cylindrical distribution and have followed explosive nucleosynthesis in the ejecta. We find that the faster rates of 40Ca(α,γ)44Ti and the slower rate of 44Ti(α,p)47V lead to more massive ejection of 44Ti and 56Ni and larger ratios <44Ti/56Ni>. Faster rotation also results in more massive ejection of 44Ti and 56Ni. Ratios <44Ti/56Ni> are however independent from rotation. Large masses of 44Ti and large ratios SUP>Ni> observed in SN 1987A and Cas A (> 1O-4M☉ and 1-2 respectively) are not realized in all the models.
[Show abstract][Hide abstract] ABSTRACT: Based on multi-dimensional neutrino-radiation hydrodynamic simulations, we report several cutting-edge issues about the long-veiled explosion mechanism of core-collapse supernovae (CCSNe). In this contribution, we pay particular attention to whether three-dimensional (3D) hydrodynamics and/or general relativity (GR) would or would not help the onset of explosions. By performing 3D simulations with spectral neutrino transport, we show that it is more difficult to obtain an explosion in 3D than in 2D. In addition, our results from the first generation of full general relativistic 3D simulations including approximate neutrino transport indicate that GR can foster the onset of neutrino-driven explosions. Based on our recent parametric studies using a light-bulb scheme, we discuss impacts of nuclear energy deposition behind the supernova shock and stellar rotation on the neutrino-driven mechanism, both of which have yet to be included in the self-consistent 3D supernova models. Finally we give an outlook with a summary of the most urgent tasks to extract the information about the explosion mechanisms from multi-messenger CCSN observables.
[Show abstract][Hide abstract] ABSTRACT: We investigate the effects of rotation on the evolution of core-collapse supernova explosion using a 15 solar mass progenitor model with a variety of neutrino luminosity and rotational velocity. Stars should have some amount of angular momentum, which would affect stellar evolution and its final explosion. In this paper we focus on the effect of rotation on gravitational collapse of a core, on a core bounce of accreting matter, and on subsequent generation and evolution of a shock wave. We find that the rotation plays a positive role for supernova explosions. More rapidly rotating models present more rapid expansion of the shock front and more energetic explosions. When the rotational speed is moderate, the shock once stalls at about 200 km away from the center similarly to a non-rotating model. Then the rotating progenitor experiences effective neutrino heating especially around an equatorial plane and explodes even with somewhat low neutrino luminosity for which the non-rotating model cannot overcome accreting matter and finally collapses. When the rotational speed is fast, the shock expands to about 300 km immediately after the core bounce and then evolves to move outward without shock stalling. We conclude that this positive effect of rotation to explosions is dominant against some possible negative aspects, for example, lower neutrino luminosity caused by less contraction of the rotating core.
[Show abstract][Hide abstract] ABSTRACT: We perform a series of simplified numerical experiments to explore how
rotation impacts on the three-dimensional (3D) hydrodynamics of core-collapse
supernovae. For the sake of our systematic study, we employ a light-bulb scheme
to trigger explosions and a three-flavor neutrino leakage scheme to treat
deleptonization effects and neutrino losses from proto-neutron star interior.
Using a 15 solar mass progenitor, we compute thirty models in 3D with a wide
variety of initial angular momentum and light-bulb neutrino luminosity. We find
that the rotation can help onset of neutrino-driven explosions for the models
in which the initial angular momentum is matched to that obtained in recent
stellar evolutionary calculations (0.3-3 rad/s at the center). For models with
larger initial angular momentum, a shock surface deforms to be more oblate due
to larger centrifugal force. This makes not only a gain region more
concentrated around the equatorial plane, but also the mass in the gain region
bigger. As a result, buoyant bubbles tend to be coherently formed and rise in
the equatorial region, which pushes the revived shock ever larger radii until a
global explosion is triggered. We find that these are the main reasons that the
preferred direction of explosion in 3D rotating models is often perpendicular
to the spin axis, which is in sharp contrast to the polar explosions around the
axis that was obtained in previous 2D simulations.
The Astrophysical Journal 03/2014; 793(1). DOI:10.1088/0004-637X/793/1/45 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We revisit potential impacts of nuclear burning on the onset of the neutrino-driven explosions of core-collapse supernovae. By changing the neutrino luminosity and its decay time to obtain parametric explosions in one- and two-dimensional (1D and 2D, respectively) models with or without a 13 isotope α network, we study how the inclusion of nuclear burning could affect the postbounce dynamics for 4 progenitor models; 3 for 15.0 M ☉ stars and 1 for an 11.2 M ☉ star. We find that the energy supply due to the nuclear burning of infalling material behind the shock can energize the shock expansion, especially for models that produce only marginal explosions in the absence of nuclear burning. These models are energized by nuclear energy deposition when the shock front passes through the silicon-rich layer and/or later as it touches the oxygen-rich layer. Depending on the neutrino luminosity and its decay time, the diagnostic energy of the explosion increases up to a few times 1050 erg for models with nuclear burning compared to the corresponding models without. We point out that these features are most remarkable for the Limongi-Chieffi progenitor in both 1D and 2D because the progenitor model possesses a massive oxygen layer, with an inner-edge radius that is smallest among the employed progenitors, which means that the shock can touch the rich fuel on a shorter timescale after bounce. The energy difference is generally smaller (~0.1-0.2 × 1051 erg) in 2D than in 1D (at most ~0.6 × 1051 erg). This is because neutrino-driven convection and the shock instability in 2D models enhance the neutrino heating efficiency, which makes the contribution of nuclear burning relatively smaller compared to 1D models. Considering uncertainties in progenitor models, our results indicate that nuclear burning should remain one of the important ingredients to foster the onset of neutrino-driven explosions.
The Astrophysical Journal 01/2014; 782(2). DOI:10.1088/0004-637X/782/2/91 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bearing in mind the application to high-magnetic-field (high-B) radio pulsars, we investigate two-dimensional (2D) thermal evolutions of neutron stars (NSs). We pay particular attention
to the influence of different equilibrium configurations on the surface temperature distributions. The equilibrium configurations
are constructed in a systematic manner, in which both toroidal and poloidal magnetic fields are determined self-consistently
with the inclusion of general relativistic effects. To solve the 2D heat transfer inside the NS interior out to the crust,
we have developed an implicit code based on a finite-difference scheme that deals with anisotropic thermal conductivity and
relevant cooling processes in the context of a standard cooling scenario. In agreement with previous studies, the surface
temperatures near the pole become higher than those in the vicinity of the equator as a result of anisotropic heat transfer.
Our results show that the ratio of the highest to the lowest surface temperatures changes maximally by one order of magnitude,
depending on the equilibrium configurations. Despite such difference, we find that the area of such hot and cold spots is
so small that the simulated X-ray spectrum could be well reproduced by a single temperature blackbody fitting.
Publications- Astronomical Society of Japan 01/2014; 66(2):50. DOI:10.1093/pasj/psu009 · 2.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present numerical results on two- (2D) and three-dimensional (3D)
hydrodynamic core-collapse simulations of an 11.2$M_\odot$ star. By changing
numerical resolutions and seed perturbations systematically, we study how the
postbounce dynamics is different in 2D and 3D. The calculations were performed
with an energy-dependent treatment of the neutrino transport based on the
isotropic diffusion source approximation scheme, which we have updated to
achieve a very high computational efficiency. All the computed models in this
work including nine 3D models and fifteen 2D models exhibit the revival of the
stalled bounce shock, leading to the possibility of explosion. All of them are
driven by the neutrino-heating mechanism, which is fostered by neutrino-driven
convection and the standing-accretion-shock instability (SASI). Reflecting the
stochastic nature of multi-dimensional (multi-D) neutrino-driven explosions,
the blast morphology changes from models to models. However, we find that the
final fate of the multi-D models whether an explosion is obtained or not, is
little affected by the explosion stochasticity. In agreement with some previous
studies, higher numerical resolutions lead to slower onset of the shock revival
in both 3D and 2D. In the context of self-consistent supernova models, our
results systematically show, for the first time, that the shock expansion
occurs more energetically in 2D than in 3D.
The Astrophysical Journal 08/2013; 786(2). DOI:10.1088/0004-637X/786/2/83 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study properties of gravitational waves (GWs) from rotating core-collapse
of a 15 solar mass star by performing three-dimensional general-relativistic
hydrodynamic simulations with an approximate neutrino transport. By
parametrically changing the precollapse angular momentum, we focus on the
effects of rotation on the GW signatures in the early postbounce evolution.
Regarding three-flavor neutrino transport, we solve the energy-averaged set of
radiation energy and momentum. In addition to the gravitational quadrupole
radiation from matter motions, we take into account GWs from anisotropic
neutrino emission. With these computations, our results present evidence that
non-axisymmetric instabilities play an essential role in determining the GW
signatures in the rotating postbounce evolution. For our rapidly rotating
models, we show that precollapse density inhomogeneities give rise to
millisecond variations in the waveforms. During prompt convection, we find that
the waveforms show narrow-band and highly quasi-periodic signals. We point out
that such feature reflects the growth of the one-armed spiral modes that
develop under the influence of the standing-accretion-shock instability and the
low-$T/|W|$ instability. The typical frequency of the quasi-periodic waveforms
can be well explained by the propagating acoustic waves. Although the GW
signals exhibit strong variability between the two polarizations and different
observer directions, they are within the realm of next generation detectors
such as by KAGRA and Advanced LIGO, if the source with sufficient angular
momentum is located in our Galaxy.
Physical Review D 04/2013; 89(4). DOI:10.1103/PhysRevD.89.044011 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We studied roles of a turbulent resistivity in the core-collapse of a
strongly magnetized massive star, carrying out 2D-resistive-MHD simulations.
The three cases with different initial strengths of magnetic field and rotation
are investigated; 1. strongly magnetized rotating core; 2.moderately magnetized
rotating core; 3. very strongly magnetized non-rotating core. In each case,
both an ideal-MHD model and resistive-MHD models are computed. As a result of
computations, each model shows a matter eruption helped by a magnetic
acceleration (and also by a centrifugal acceleration in the rotating cases). We
found that a resistivity attenuates the explosion in case~1 and 2, while it
enhances the explosion in case~3. We also found that in the rotating cases,
main mechanisms for the amplification of a magnetic field in the post-bounce
phase are an outward advection of magnetic field and a winding of poloidal
magnetic field-lines by differential rotation, which are somewhat dampened down
with the presence of a resistivity. Although the magnetorotational instability
seems to occur in the rotating models, it will play only a minor role in a
magnetic field amplification. Another impact of resistivity is that on the
aspect ratio. In the rotating cases, a large aspect ratio of the ejected
matters, $> 2.5$, attained in a ideal-MHD model is reduced to some extent in a
resistive model. These results indicate that a resistivity possibly plays an
important role in the dynamics of strongly magnetized supernovae.
The Astrophysical Journal 11/2012; 764(1). DOI:10.1088/0004-637X/764/1/10 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We performed hydrodynamic simulations of core collapse and bounce for a progenitor model with 15.0 solar mass, using ZEUS-MP code in axi-symmetric coordinate. Our numerical code is equipped with a nuclear reaction network including 13 alpha nuclei form {sup 4}He to {sup 56}Ni to investigate the potential role played by nuclear reactions in reviving a stalled shock wave at the central region of core-collapse supernovae. We found that the energy released by nuclear reactions is significantly helpful in accelerating shock waves and is able to produce energetic explosion even if inputted neutrino luminosity is low.
[Show abstract][Hide abstract] ABSTRACT: We examine explosive nucleosynthesis during neutrino-driven, aspherical supernovae of Population III stars, based on two-dimensional (2D) hydrodynamic simulations of the explosion of 11-40M{sub Circled-Dot-Operator} stars with zero metallicity. The magnitude and asymmetry of the explosion energy are estimated with the simulations. By post-processing calculations with a large nuclear reaction network, we have evaluated abundances and masses of ejecta from the aspherical SNe. We find that the evaluated abundance patterns are similar to those observed in extremely metal poor stars, as shown in spherical and 2D models, in which the explosion is manually and spherically initiated. Matter mixing induced via standing accretion shock instability is important for the abundances and masses of the SN ejecta.
[Show abstract][Hide abstract] ABSTRACT: We investigate the nucleosynthesis during the stellar evolution and the jet-like supernova explosion of a massive star of 70 M{sub Circled-Dot-Operator} having the solar metallicity in the main sequence stage. The nucleosynthesis calculations have been performed with large nuclear reaction networks, where the weak s-, p-, and r-processes are taken into account. As a result s-elements of 60 > A > 90 and r-elements of 90 > A > 160 are highly overproduced relative to the solar system abundances. We find that the Sr-Y-Zr isotopes are primarily synthesized in the explosive nucleosynthesis which could be one of the sites of the lighter element primary process (LEPP).
[Show abstract][Hide abstract] ABSTRACT: Bearing in mind the application of core-collapse supernovae, we study the nonlinear properties of the magnetorotational instability (MRI) by means of three-dimensional simulations in the framework of a local shearing box approximation. By systematically changing the shear rates that symbolize the degree of differential rotation in nascent proto-neutron stars (PNSs), we derive a scaling relation between the turbulent stress sustained by the MRI and the shear-vorticity ratio. Our parametric survey shows a power-law scaling between the turbulent stress (((w {sub tot}))) and the shear-vorticity ratio (g{sub q} ) as ((w {sub tot})){proportional_to}g {sup {delta}} {sub q} with an index of {delta} {approx} 0.5. The MRI-amplified magnetic energy has a similar scaling relative to the turbulent stress, while the Maxwell stress has a slightly smaller power-law index ({approx}0.36). By modeling the effect of viscous heating rates from MRI turbulence, we show that the stronger magnetic fields, or the larger shear rates initially imposed, lead to higher dissipation rates. For a rapidly rotating PNS with a spin period in milliseconds and with strong magnetic fields of 10{sup 15} G, the energy dissipation rate is estimated to exceed 10{sup 51} erg s{sup -1}. Our results suggest that the conventional magnetohydrodynamic (MHD) mechanism of core-collapse supernovae is likely to be affected by MRI-driven turbulence, which we speculate, on the one hand, could harm the MHD-driven explosions due to the dissipation of the shear rotational energy at the PNS surface; or, on the other hand, its energy deposition might be potentially favorable for the working of the neutrino-heating mechanism.
The Astrophysical Journal 11/2012; 759(2). DOI:10.1088/0004-637X/759/2/110 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have performed three-dimensional (3D) hydrodynamical simulations of
core-collapse supernovae (SNe) with multigroup neutrino transport to
study non-axisymmetric effects in the context of neutrino heating
explosion mechanism. By comparing one- (1D) and two dimensional (2D)
results with those of 3D, we study how the increasing spatial
multi-dimensionality affects the postbounce SN dynamics. The
calculations were performed with an energy-dependent treatment of the
neutrino transport that is solved by the isotropic diffusion source
approximation scheme. In agreement with previous studies, our 1D model
does not produce explosions for the 11.2 M ⊙ star, while
the neutrino-driven revival of the stalled bounce shock is obtained both
in the 2D and 3D models. Our results show that convective matter motions
below the gain radius become much more violent in 3D than 2D, making the
neutrino luminosity larger for 3D. Enhanced by the large neutrino
luminosity, the shock of the 3D model expands faster than that of the
2D. Our results show that the evolution of the shock is sensitive to the
employed numerical resolutions. To draw a robust conclusion, 3D
simulations with much higher numerical resolution and more advanced
treatment of neutrino transport and gravity is needed.
Proceedings of the International Astronomical Union 09/2012; 7(S279):409-410. DOI:10.1017/S1743921312013580