Massive stars end their lives in explosions with kinetic energies on the order of 10 51 erg. Immediately after the explosion has been launched, a region of low density and high entropy forms behind the ejecta, which is continuously subject to neutrino heating. The neutrinos emitted from the remnant at the center, the protoneutron star (PNS), heat the material above the PNS surface. This heat is partly converted into kinetic energy, and the material accelerates to an outflow that is known as the neutrino-driven wind. For the first time we simulate the collapse, bounce, explosion, and the neutrino-driven wind phases consistently over more than 20 s. Our numerical model is based on spherically symmetric general relativistic radiation hydrodynamics using spectral three-flavor Boltzmann neutrino transport. In simulations where no explosions are obtained naturally, we model neutrino-driven explosions for low-and intermediatemass Fe-core progenitor stars by enhancing the charged current reaction rates. In the case of a special progenitor star, the 8.8 M O-Ne-Mg-core, the explosion in spherical symmetry was obtained without enhanced opacities. The post-explosion evolution is in qualitative agreement with static steady-state and parametrized dynamic models of the neutrino-driven wind. On the other hand, we generally find lower neutrino luminosities and mean neutrino energies, as well as a different evolutionary behavior of the neutrino luminosities and mean neutrino energies. The neutrino-driven wind is proton-rich for more than 10 s and the contraction of the PNS differs from the assumptions made for the conditions at the inner boundary in previous neutrino-driven wind studies. Despite the moderately high entropies of about 100 k B /baryon and the fast expansion timescales, the conditions found in our models are unlikely to favor r-process nucleosynthesis. The simulations are carried out until the neutrino-driven wind settles down to a quasi-stationary state. About 5 s after the bounce, the peak temperature inside the PNS already starts to decrease because of the continued deleptonization. This moment determines the beginning of a cooling phase dominated by the emission of neutrinos. We discuss the physical conditions of the quasi-static PNS evolution and take the effects of deleptonization and mass accretion from early fallback into account.

Many of the currently available equations of state for core-collapse supernova simulations give large neutron star radii and do not provide large enough neutron star masses, both of which are inconsistent with some recent neutron star observations. In addition, one of the critical uncertainties in the nucleon-nucleon interaction, the nuclear symmetry energy, is not fully explored by the currently available equations of state. In this article, we construct two new equations of state which match recent neutron star observations and provide more flexibility in studying the dependence on nuclear matter properties. The equations of state are also provided in tabular form, covering a wide range in density, temperature and asymmetry, suitable for astrophysical simulations. These new equations of state are implemented into our spherically symmetric core-collapse supernova model, which is based on general relativistic radiation hydrodynamics with three-flavor Boltzmann neutrino transport. The results are compared with commonly used equations of state in supernova simulations of 15 and 40 M ⊙ progenitors. We do not find any simple correlations between individual nuclear matter properties at saturation and the outcome of these simulations. However, the new equations of state lead to the most compact neutron stars among the relativistic mean-field models which we considered. The new models also obey the previously observed correlation between the time to black hole formation and the maximum mass of an s = 4 neutron star.

We revise the bound from the supernova SN1987A on the coupling of ultralight axion-like particles (ALPs) to photons. In a core-collapse supernova, ALPs would be emitted via the Primakoff process, and eventually convert into gamma rays in the magnetic field of the Milky Way. The lack of a gamma-ray signal in the GRS instrument of the SMM satellite in coincidence with the observation of the neutrinos emitted from SN1987A therefore provides a strong bound on their coupling to photons. Due to the large uncertainty associated with the current bound, we revise this argument, based on state-of-the-art physical inputs both for the supernova models and for the Milky-Way magnetic field. Furthermore, we provide major amendments, such as the consistent treatment of nucleon-degeneracy effects and of the reduction of the nuclear masses in the hot and dense nuclear medium of the supernova. With these improvements, we obtain a new upper limit on the photon-ALP coupling: g aγ 5.3 × 10 −12 GeV −1 , for m a 4.4 × 10 −10 eV , and we also give its dependence at larger ALP masses m a . Moreover, we discuss how much the Fermi-LAT satellite experiment could improve this bound, should a close-enough supernova explode in the near future.

We identify an observable imprint of a first-order hadron-quark phase transition at supranuclear densities on the gravitational-wave (GW) emission of neutron star mergers. Specifically, we show that the dominant postmerger GW frequency f peak may exhibit a significant deviation from an empirical relation between f peak and the tidal deformability if a strong first-order phase transition leads to the formation of a gravitationally stable extended quark matter core in the postmerger remnant. A comparison of the GW signatures from a large, representative sample of microphysical, purely hadronic equations of state indicates that this imprint is only observed in those systems which undergo a strong first-order phase transition. Such a shift of the dominant postmerger GW frequency can be revealed by future GW observations, which would provide evidence for the existence of a strong first-order phase transition in the interior of neutron stars.PACS numbers: 04.30. Tv,26.60.Kp,26.60Dd,97.60.Jd Introduction: The theory of strong interactions, quantum chromodynamics (QCD), with quarks and gluons as fundamental degrees of freedom predicts a transition from nuclear matter to quark matter. At vanishing baryonic chemical potential, numerical solutions of QCD are available, which state a smooth crossover transition at a temperature of T = 154 ± 9 MeV [1][2][3]. At finite baryon densities only phenomenological models of QCD exist, which are benchmarked by nuclear matter phenomenology around nuclear saturation density ρ sat ≈ 2.7×10 14 g cm −3 [4] and by perturbative QCD at asymptotic densities [5]. Those methods, however, are not applicable in the region of the hadron-quark transition. Hence, the nature of the transition to quark matter (crossover or first-order phase transition) remains unclear. Whether the hadron-quark phase transition occurs at conditions which are found in compact stellar objects, e.g., in neutron stars (NS) with central densities of several times ρ sat , is presently unknown. The very first detection of gravitational waves (GW) from a NS merger [6] highlights the prospect to learn about the presence and the nature of the QCD phase transition in stellar objects, e.g. [7][8][9][10][11][12][13][14][15].

We explore the implications of the QCD phase transition during the postbounce evolution of corecollapse supernovae. Using the MIT bag model for the description of quark matter and assuming small bag constants, we find that the phase transition occurs during the early postbounce accretion phase. This stage of the evolution can be simulated with general relativistic three-flavor Boltzmann neutrino transport. The phase transition produces a second shock wave that triggers a delayed supernova explosion. If such a phase transition happens in a future galactic supernova, its existence and properties should become observable as a second peak in the neutrino signal that is accompanied by significant changes in the energy of the emitted neutrinos. In contrast to the first neutronization burst, this second neutrino burst is dominated by the emission of anti-neutrinos because the electrondegeneracy is lifted when the second shock passes through the previously neutronized matter. In search of the phase transition from hadronic to deconfined matter, heavy ion experiments at RHIC and at LHC at CERN explore the QCD phase diagram for large temperatures and small baryochemical potentials. For these conditions, which were also present in the early universe, lattice QCD calculations predict a crossover transition between the deconfined chirally symmetric phase and the confined phase with broken chiral symmetry. For high chemical potentials and low temperatures a first order chiral phase transition is expected and will be tested at the FAIR facility at GSI Darmstadt.Due to their large central densities, compact stars can also serve as laboratories for nuclear matter beyond saturation density and may contain quark matter [1]. The formation of quark matter in compact stars is mainly discussed in two scenarios, in protoneutron stars (PNS) after the supernova explosion [2] and in old accreting neutron stars [3,4]. For the first case, deleptonization leads to the loss of lepton pressure and therefore to an increase in the central density so that the phase transition takes place. Possible observables are the emission of gravitational waves [3,4] due to the contraction of the neutron star or delayed γ-ray bursts [5].In this article we want to follow a third and less discussed case. The phase transition from hadronic to quark matter can already occur in the early postbounce phase of a core-collapse supernova [6,7,8,9,10]. This requires a phase transition onset close to saturation density, which can be realized for high temperatures and low proton fractions. For such a scenario Ref. [8] found the formation of a second shock as a direct consequence of the phase transition. However, the lack of neutrino transport in their model allowed them to investigate the dynamics only for a few ms after bounce. Very recently, a quark matter phase transition has been considered with Boltzmann neutrino transport for a 100 M ⊙ progenitor [11]. The appearance of quark matter shortened the time until black hole formation due to the softening of the equation o...

We discuss three new equations of state (EOS) in core-collapse supernova simulations. The new EOS are based on the nuclear statistical equilibrium model of Hempel and Schaffner-Bielich (HS), which includes excluded volume effects and relativistic mean-field (RMF) interactions. We consider the RMF parameterizations TM1, TMA, and FSUgold. These EOS are implemented into our spherically symmetric core-collapse supernova model, which is based on general relativistic radiation hydrodynamics and three-flavor Boltzmann neutrino transport. The results obtained for the new EOS are compared with the widely used EOS of H. Shen et al. and Lattimer & Swesty. The systematic comparison shows that the model description of inhomogeneous nuclear matter is as important as the parameterization of the nuclear interactions for the supernova dynamics and the neutrino signal. Furthermore, several new aspects of nuclear physics are investigated: the HS EOS contains distributions of nuclei, including nuclear shell effects. The appearance of light nuclei, e.g., deuterium and tritium is also explored, which can become as abundant as alphas and free protons. In addition, we investigate the black hole formation in failed core-collapse supernovae, which is mainly determined by the high-density EOS. We find that temperature effects lead to a systematically faster collapse for the non-relativistic LS EOS in comparison to the RMF EOS. We deduce a new correlation for the time until black hole formation, which allows to determine the maximum mass of proto-neutron stars, if the neutrino signal from such a failed supernova would be measured in the future. This would give a constraint for the nuclear EOS at finite entropy, complementary to observations of cold neutron stars.

The stellar mass range 8 M/M 12 corresponds to the most massive asymptotic giant branch (AGB) stars and the most numerous massive stars. It is host to a variety of supernova (SN) progenitors and is therefore very important for galactic chemical evolution and stellar population studies. In this paper, we study the transition from super-AGB (SAGB) star to massive star and find that a propagating neon-oxygen-burning shell is common to both the most massive electron capture supernova (EC-SN) progenitors and the lowest mass iron-core-collapse supernova (FeCCSN) progenitors. Of the models that ignite neon-burning off-center, the 9.5 M star would evolve to an FeCCSN after the neon-burning shell propagates to the center, as in previous studies. The neon-burning shell in the 8.8 M model, however, fails to reach the center as the URCA process and an extended (0.6 M ) region of low Y e (0.48) in the outer part of the core begin to dominate the late evolution; the model evolves to an EC-SN. This is the first study to follow the most massive EC-SN progenitors to collapse, representing an evolutionary path to EC-SN in addition to that from SAGB stars undergoing thermal pulses (TPs). We also present models of an 8.75 M SAGB star through its entire TP phase until electron captures on 20 Ne begin at its center and of a 12 M star up to the iron core collapse. We discuss key uncertainties and how the different pathways to collapse affect the pre-SN structure. Finally, we compare our results to the observed neutron star mass distribution.

Astrophysical observations originate from matter that interacts with radiation or transported particles. We develop a pragmatic approximation in order to enable multi-dimensional simulations with basic spectral radiative transfer when the available computational resources are not sufficient to solve the complete Boltzmann transport equation. The distribution function of the transported particles is decomposed into a trapped particle component and a streaming particle component. Their separate evolution equations are coupled by a source term that converts trapped particles into streaming particles. We determine this source term by requiring the correct diffusion limit for the evolution of the trapped particle component. For a smooth transition to the free streaming regime, this 'diffusion source' is limited by the matter emissivity. The resulting streaming particle emission rates are integrated over space to obtain the streaming particle flux. Finally, a geometric estimate of the flux factor is used to convert the particle flux to the streaming particle density, which enters the evaluation of streaming particle-matter interactions. The efficiency of the scheme results from the freedom to use different approximations for each particle component. In supernovae, for example, reactions with trapped particles on fast time scales establish equilibria that reduce the number of primitive variables required to evolve the trapped particle component. On the other hand, a stationary-state approximation considerably facilitates the treatment of the streaming particle component. Different approximations may apply in applications to stellar atmospheres, star formation, or cosmological radiative transfer. We compare the isotropic diffusion source approximation with Boltzmann neutrino transport of electron flavour neutrinos in spherically symmetric supernova models and find good agreement. An extension of the scheme to the multi-dimensional case is also discussed.