| 1. |
- Eggenberger Andersen, Oliver, et al.
(author)
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Equation-of-state Dependence of Gravitational Waves in Core-collapse Supernovae
- 2021
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 923:2
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Journal article (peer-reviewed)abstract
- Gravitational waves (GWs) provide unobscured insight into the birthplace of neutron stars and black holes in core-collapse supernovae (CCSNe). The nuclear equation of state (EOS) describing these dense environments is yet uncertain, and variations in its prescription affect the proto−neutron star (PNS) and the post-bounce dynamics in CCSN simulations, subsequently impacting the GW emission. We perform axisymmetric simulations of CCSNe with Skyrme-type EOSs to study how the GW signal and PNS convection zone are impacted by two experimentally accessible EOS parameters, (1) the effective mass of nucleons, m⋆, which is crucial in setting the thermal dependence of the EOS, and (2) the isoscalar incompressibility modulus, Ksat. While Ksat shows little impact, the peak frequency of the GWs has a strong effective mass dependence due to faster contraction of the PNS for higher values of m⋆ owing to a decreased thermal pressure. These more compact PNSs also exhibit more neutrino heating, which drives earlier explosions and correlates with the GW amplitude via accretion plumes striking the PNS, exciting the oscillations. We investigate the spatial origin of the GWs and show the agreement between a frequency-radial distribution of the GW emission and a perturbation analysis. We do not rule out overshoot from below via PNS convection as another moderately strong excitation mechanism in our simulations. We also study the combined effect of effective mass and rotation. In all our simulations we find evidence for a power gap near ∼1250 Hz; we investigate its origin and report its EOS dependence.
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| 2. |
- Lin, Zidu, et al.
(author)
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Detectability of neutrino-signal fluctuations induced by the hadron-quark phase transition in failing core-collapse supernovae
- 2024
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In: Physical Review D. - 2470-0010 .- 2470-0029. ; 109:2
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Journal article (peer-reviewed)abstract
- We introduce a systematic and quantitative methodology for establishing the presence of neutrino oscillatory signals due to the hadron-quark phase transition (PT) in failing core-collapse supernovae from the observed neutrino event rate in water- or ice-based neutrino detectors. The methodology uses a likelihood ratio in the frequency domain as a test-statistic; it is employed for quantitative analysis of neutrino signals without assuming the frequency, amplitude, starting time, and duration of the PT-induced oscillations present in the neutrino events and thus it is suitable for analyzing neutrino signals from a wide variety of numerical simulations. We test the validity of this method by using a core-collapse simulation of a 17 solar-mass star by Zha et al. [Astrophys. J. 911, 74 (2021) ]. Based on this model, we further report the presence of a PT-induced oscillations quantitatively for a core-collapse supernovae out to a distance of ∼10 kpc, ∼5 kpc for IceCube and to a distance of ∼10 kpc, ∼5 kpc, and ∼1 kpc for a 0.4 Mt mass water Cherenkov detector. This methodology will aid the investigation of a future galactic supernova and the study of hadron-quark phase in the core of core-collapse supernovae.
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| 3. |
- Zha, Shuai, et al.
(author)
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Gravitational-wave Signature of a First-order Quantum Chromodynamics Phase Transition in Core-Collapse Supernovae
- 2020
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 125:5
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Journal article (peer-reviewed)abstract
- A first-order quantum chromodynamics (QCD) phase transition (PT) may take place in the protocompact star (PCS) produced by a core-collapse supernova (CCSN). In this work, we study the consequences of such a PT in a nonrotating CCSN with axisymmetric hydrodynamic simulations. We find that the PT leads to the collapse of the PCS and results in a loud burst of gravitational waves (GWs). The amplitude of this GW burst is similar to 30 times larger than the postbounce GW signal normally found for nonrotating CCSN. It shows a broad peak at high frequencies (similar to 2500-4000 Hz) in the spectrum, has a duration of less than or similar to 5 ms, and carries similar to 3 orders of magnitude more energy than the other episodes. Also, the peak frequency of the PCS oscillation increases dramatically after the Fr-induced collapse. In addition to a second neutrino burst, the GW signal, if detected by the ground-based GW detectors, is decisive evidence of the first-order QCD PT inside CCSNe and provides key information about the structure and dynamics of the PCS.
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| 4. |
- Zha, Shuai, et al.
(author)
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Hydrodynamic simulations of electron-capture supernovae : progenitor and dimension dependence
- 2022
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 513:1, s. 1317-1328
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Journal article (peer-reviewed)abstract
- We present neutrino-transport hydrodynamic simulations of electron-capture supernovae (ECSNe) in FLASH with new two-dimensional (2D) collapsing progenitor models. These progenitor models feature the 2D modelling of oxygen-flame propagation until the onset of core collapse. We perform axisymmetric simulations with six progenitor models that, at the time of collapse, span a range of propagating flame front radii. For comparison, we also perform a simulation with the same set-up using the canonical, spherically symmetrical progenitor model n8.8. We found that the variations in the progenitor models inherited from simulations of stellar evolution and flame propagation do not significantly alter the global properties of the neutrino-driven ECSN explosion, such as the explosion energy (∼1.36–1.48 × 1050 erg) and the mass (∼0.017–0.018 M⊙) and composition of the ejecta. Due to aspherical perturbations induced by the 2D flame, the ejecta contains a small amount (≲1.8 × 10−3 M⊙) of low-Ye (0.35 < Ye < 0.4) component. The baryonic mass of the protoneutron star is ∼1.34 M⊙ (∼1.357 M⊙) with the new (n8.8) progenitor models when simulations end at ∼400 ms and the discrepancy is due to updated weak-interaction rates in the progenitor evolutionary simulations. Our results reflect the nature of ECSN progenitors containing a strongly degenerate oxygen–neon–magnesium (ONeMg) core and suggest a standardized ECSN explosion initialized by ONeMg core collapse. Moreover, we carry out a rudimentary three-dimensional simulation and find that the explosion properties are fairly compatible with the 2D counterpart. Our paper facilitates a more thorough understanding of ECSN explosions following the ONeMg core collapse, though more three-dimensional simulations are still needed.
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| 5. |
- Zha, Shuai, et al.
(author)
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Impact of rotation on the multimessenger signatures of a hadron-quark phase transition in core-collapse supernovae
- 2022
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In: Physical Review D. - 2470-0010 .- 2470-0029. ; 106:12
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Journal article (peer-reviewed)abstract
- We study the impact of rotation on the multimessenger signals of core-collapse supernovae (CCSNe) with the occurrence of a first-order hadron-quark phase transition (HQPT). We simulate CCSNe with the flash code starting from a 20 M⊙ progenitor with different rotation rates, and using the RDF equation of state from Bastian 2021 that prescribes the HQPT. Rotation is found to delay the onset of the HQPT and the resulting dynamical collapse of the protocompact star (PCS) due to the centrifugal support. All models with the HQPT experience a second bounce shock which leads to a successful explosion. The oblate PCS as deformed by rotation gives rise to strong gravitational-wave (GW) emission around the second bounce with a peak amplitude larger by a factor of ∼10 than that around the first bounce. The breakout of the second bounce shock at the neutrinosphere produces a ¯νe-rich neutrino burst with a luminosity of serveral 1053 erg s−1. In rapidly rotating models the PCS pulsation following the second bounce generates oscillations in the neutrino signal after the burst. In the fastest rotating model with the HQPT, a clear correlation is found between the oscillations in the GW and neutrino signals immediately after the second bounce. In addition, the HQPT-induced collapse leads to a jump in the ratio of rotational kinetic energy to gravitational energy (β) of the PCS, for which persistent GW emission may arise due to secular nonaxisymmetric instabilities.
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| 6. |
- Zha, Shuai, et al.
(author)
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Progenitor Dependence of Hadron-quark Phase Transition in Failing Core-collapse Supernovae
- 2021
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 911:2
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Journal article (peer-reviewed)abstract
- We study the consequences of a hadron-quark phase transition (PT) in failing core-collapse supernovae (CCSNe) that give birth to stellar-mass black holes (BH). We perform a suite of neutrino-transport general-relativistic hydrodynamic simulations in spherical symmetry with 21 progenitor models and a hybrid equation of state (EoS) including hadrons and quarks. We find that the effect of the PT on the CCSN postbounce dynamics is a function of the bounce compactness parameter xi(2.2). For xi(2.2) greater than or similar to 0.24, the PT leads to a second dynamical collapse of the protocompact star (PCS). While BH formation starts immediately after this second collapse for models with xi(2.2) greater than or similar to 0.51, the PCS experiences a second bounce and oscillations for models with 0.24 less than or similar to x xi(2.2) less than or similar to 0.51. These models emit potent oscillatory neutrino signals with a period of similar to 1 ms for tens of milliseconds after the second bounce, which can be a strong indicator of the PT in failing CCSNe if detected in the future. However, no shock revival occurs and BH formation inevitably takes place in our spherically symmetric simulations. Furthermore, via a diagram of mass-specific entropy evolution of the PCS, the progenitor dependence can be understood through the appearance of a third family of compact stars emerging at large entropy induced by the PT.
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| 7. |
- Zha, Shuai, et al.
(author)
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Unveiling the nature of gravitational-wave emission in core-collapse supernovae with perturbative analysis
- 2024
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In: Physical Review D. - 2470-0010 .- 2470-0029. ; 109:8
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Journal article (peer-reviewed)abstract
- Gravitational waves (GWs) can provide crucial information about the central engines of core-collapse supernovae (CCSNe). In order to unveil the nature of GW emission in CCSNe, we apply perturbative analyses with the same underlying equations as simulations to diagnose oscillations of the proto-neutron star (PNS) during ∼1 s postbounce. In the pseudo-Newtonian case, we find that radial profiles of GW emission match well between the perturbative analysis with ?=2 and simulations inside the PNS at any frequency and time. This confirms that the GW emission of CCSNe arises from the global PNS oscillations in the perturbative regime. Based on this, we solve for the discrete eigenmodes with a free PNS surface and tentatively identify a set of ? modes and the ? mode contributing to the peak GW emission. We also offer a possible explanation for the power gap in the GW spectrum found in simulations that lies at the frequency with vanishing cumulative emission of the PNS. Our results enhance the predictive power of perturbative analyses in the GW signals of CCSNe.
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