43 research outputs found
Multi-dimensional Core-Collapse Supernova Simulations with Neutrino Transport
We present multi-dimensional core-collapse supernova simulations using the
Isotropic Diffusion Source Approximation (IDSA) for the neutrino transport and
a modified potential for general relativity in two different supernova codes:
FLASH and ELEPHANT. Due to the complexity of the core-collapse supernova
explosion mechanism, simulations require not only high-performance computers
and the exploitation of GPUs, but also sophisticated approximations to capture
the essential microphysics. We demonstrate that the IDSA is an elegant and
efficient neutrino radiation transfer scheme, which is portable to multiple
hydrodynamics codes and fast enough to investigate long-term evolutions in two
and three dimensions. Simulations with a 40 solar mass progenitor are presented
in both FLASH (1D and 2D) and ELEPHANT (3D) as an extreme test condition. It is
found that the black hole formation time is delayed in multiple dimensions and
we argue that the strong standing accretion shock instability before black hole
formation will lead to strong gravitational waves.Comment: 3 pages, proceedings for Nuclei in the Cosmos XIV, Niigata, Japan
(2016
Two-Dimensional Core-Collapse Supernova Simulations with the Isotropic Diffusion Source Approximation for Neutrino Transport
The neutrino mechanism of core-collapse supernova is investigated via
non-relativistic, two-dimensional (2D), neutrino radiation-hydrodynamic
simulations. For the transport of electron flavor neutrinos, we use the
interaction rates defined by Bruenn (1985) and the isotropic diffusion source
approximation (IDSA) scheme, which decomposes the transported particles into
trapped particle and streaming particle components. Heavy neutrinos are
described by a leakage scheme. Unlike the "ray-by-ray" approach in some other
multi-dimensional supernova models, we use cylindrical coordinates and solve
the trapped particle component in multiple dimensions, improving the
proto-neutron star resolution and the neutrino transport in angular and
temporal directions. We provide an IDSA verification by performing 1D and 2D
simulations with 15 and 20 progenitors from Woosley et al.~(2007) and
discuss the difference of our IDSA results with those existing in the
literature. Additionally, we perform Newtonian 1D and 2D simulations from
prebounce core collapse to several hundred milliseconds postbounce with 11, 15,
21, and 27 progenitors from Woosley et al.~(2002) with the HS(DD2)
equation of state. General relativistic effects are neglected. We obtain robust
explosions with diagnostic energies ~B for all
considered 2D models within approximately milliseconds after bounce
and find that explosions are mostly dominated by the neutrino-driven
convection, although standing accretion shock instabilities are observed as
well. We also find that the level of electron deleptonization during collapse
dramatically affect the postbounce evolution, e.g.~the ignorance of
neutrino-electron scattering during collapse will lead to a stronger explosion.Comment: 23 pages. Accepted for publication in Ap
Massive Stars and their Supernovae
Massive stars and their supernovae are prominent sources of radioactive
isotopes, the observations of which thus can help to improve our astrophysical
models of those. Our understanding of stellar evolution and the final explosive
endpoints such as supernovae or hypernovae or gamma-ray bursts relies on the
combination of magneto-hydrodynamics, energy generation due to nuclear
reactions accompanying composition changes, radiation transport, and
thermodynamic properties (such as the equation of state of stellar matter).
Nuclear energy production includes all nuclear reactions triggered during
stellar evolution and explosive end stages, also among unstable isotopes
produced on the way. Radiation transport covers atomic physics (e.g. opacities)
for photon transport, but also nuclear physics and neutrino nucleon/nucleus
interactions in late phases and core collapse. Here we want to focus on the
astrophysical aspects, i.e. a description of the evolution of massive stars and
their endpoints, with a special emphasis on the composition of their ejecta (in
form of stellar winds during the evolution or of explosive ejecta). Low and
intermediate mass stars end their evolution as a white dwarf with an unburned C
and O composition. Massive stars evolve beyond this point and experience all
stellar burning stages from H over He, C, Ne, O and Si-burning up to core
collapse and explosive endstages. In this chapter we discuss the
nucleosynthesis processes involved and the production of radioactive nuclei in
more detail.Comment: 79 pages; Chapter of "Astronomy with Radioactivities", a book in
Springer's 'lecture notes in physics series, Vol. 812, Eds. Roland Diehl,
Dieter H. Hartmann, and Nikos Prantzos, to appear in summer 201
PUSHing Core-Collapse Supernovae to Explosions in Spherical Symmetry: Nucleosynthesis Yields
Core-collapse supernovae (CCSNe) are the extremely energetic deaths of
massive stars. They play a vital role in the synthesis and dissemination of
many heavy elements in the universe. In the past, CCSN nucleosynthesis
calculations have relied on artificial explosion methods that do not adequately
capture the physics of the innermost layers of the star. The PUSH method,
calibrated against SN1987A, utilizes the energy of heavy-flavor neutrinos
emitted by the proto-neutron star (PNS) to trigger parametrized explosions.
This makes it possible to follow the consistent evolution of the PNS and to
ensure a more accurate treatment of the electron fraction of the ejecta. Here,
we present the Iron group nucleosynthesis results for core-collapse supernovae,
exploded with PUSH, for two different progenitor series. Comparisons of the
calculated yields to observational metal-poor star data are also presented.
Nucleosynthesis yields will be calculated for all elements and over a wide
range of progenitor masses. These yields can be immensely useful for models of
galactic chemical evolution.Comment: 3 pages, 3 figures, poster presentation to appear in the proceedings
of the 14th International Symposium on Nuclei in the Cosmos (NIC-XIV), Ed. S.
Kubono, JPS (Japan Physical Society
Astrophysical Implications of the QCD phase transition
The possible role of a first order QCD phase transition at nonvanishing quark chemical potential and temperature for cold neutron stars and for supernovae is delineated. For cold neutron stars, we use the NJL model with nonvanishing color superconducting pairing gaps, which describes the phase transition to the 2SC and the CFL quark matter phases at high baryon densities. We demonstrate that these two phase transitions can both be present in the core of neutron stars and that they lead to the appearance of a third family of solution for compact stars. In particular, a core of CFL quark matter can be present in stable compact star configurations when slightly adjusting the vacuum pressure to the onset of the chiral phase transition from the hadronic model to the NJL model. We show that a strong first order phase transition can have strong impact on the dynamics of core collapse supernovae. If the QCD phase transition sets in shortly after the first bounce, a second outgoing shock wave can be generated which leads to an explosion. The presence of the QCD phase transition can be read off from the neutrino and antineutrino signal of the supernova
Explosion Dynamics of Parametrized Spherically Symmetric Core-Collapse Supernova Simulations
We report on a method, PUSH, for triggering core-collapse supernova (CCSN)
explosions of massive stars in spherical symmetry. This method provides a
framework to study many important aspects of core collapse supernovae: the
effects of the shock passage through the star, explosive supernova
nucleosynthesis and the progenitor-remnant connection. Here we give an overview
of the method, compare the results to multi-dimensional simulations and
investigate the effects of the progenitor and the equation of state on black
hole formation.Comment: Proceedings for Nuclei in the Cosmos XIV, Niigata, Japan (2016
New aspects of the QCD phase transition in proto-neutron stars and core-collapse supernovae
The QCD phase transition from hadronic to deconfined quark matter is found to be a so-called "entropic" phase transition, characterized, e.g., by a negative slope of the phase transition line in the pressure-temperature phase diagram. In a first part of the present proceedings it is discussed that entropic phase transitions lead to unusual thermal properties of the equation of state (EoS). For example one finds a loss of pressure (a "softening") of the proto-neutron star EoS with increasing entropy. This can lead to a novel, hot third family of compact stars, which exists only in the early proto-neutron star phase. Such a hot third family can trigger explosions of core-collapse supernovae. However, so far this special explosion mechanism was found to be working only for EoSs which are not compatible with the 2 M⊙ constraint for the neutron star maximum mass. In a second part of the proceeding it is discussed which quark matter parameters could be favorable for this explosion mechanism, and have sufficiently high maximum masses at the same time
Stellar Mass Black Hole Formation and Multi-messenger Signals from Three Dimensional Rotating Core-Collapse Supernova Simulations
We present self-consistent, 3D core-collapse supernova simulations of a 40
progenitor model using the isotropic diffusion source approximation
for neutrino transport and an effective general relativistic potential up to
~s~postbounce. We consider three different rotational speeds with
initial angular velocities of ,~0.5, and~1~rad~s and
investigate the impact of rotation on shock dynamics, black hole formation, and
gravitational wave signals. The rapidly-rotating model undergoes an early
explosion at ~ms postbounce and shows signs of the low
instability. We do not find black hole formation in this model within ~ms postbounce. In contrast, we find black hole formation at
776~ms~postbounce and 936~ms~postbounce for the non-rotating and
slowly-rotating models, respectively. The slowly-rotating model explodes at
~ms postbounce and fallback accretion onto the proto-neutron star
(PNS) results in BH formation. In addition, the
standing~accretion~shock~instability could induce rotation on the proto-neutron
star with a non-rotating progenitor and gives a black~hole spin parameter of
, if the specific angular momentum is conserved during black hole
formation. But for the non-rotating model, without an explosion, all the
angular momentum should eventually be accreted by the BH, resulting in a
non-spinning BH. The successful explosion of the slowly-rotating model
drastically slows accretion onto the PNS allowing continued cooling and
contraction that results in an extremely high gravitational-wave frequency
(~Hz) at black~hole formation, while the non-rotating model
generates gravitational wave signals similar to its 2D counterpart.Comment: 14 pages, 11 figure
On the Importance of the Equation of State for the Neutrino-Driven Supernova Explosion Mechanism
By implementing widely-used equations of state (EOS) from Lattimer & Swesty
(LS) and H. Shen et al. (SHEN) in core-collapse supernova simulations, we
explore possible impacts of these EOS on the post-bounce dynamics prior to the
onset of neutrino-driven explosions. Our spherically symmetric (1D) and axially
symmetric (2D) models are based on neutrino radiation hydrodynamics including
spectral transport, which is solved by the isotropic diffusion source
approximation. We confirm that in 1D simulations neutrino-driven explosions
cannot be obtained for any of the employed EOS. Impacts of the EOS on the
post-bounce hydrodynamics are more clearly visible in 2D simulations. In 2D
models of a 15 M_sun progenitor using the LS EOS, the stalled bounce shock
expands to increasingly larger radii, which is not the case using the SHEN EOS.
Keeping in mind that the omission of the energy drain by heavy-lepton neutrinos
in the present scheme could facilitate explosions, we find that 2D models of an
11.2 M_sun progenitor produce neutrino-driven explosions for all the EOS under
investigation. Models using the LS EOS are slightly more energetic compared to
those with the SHEN EOS. The more efficient neutrino heating in the LS models
coincides with a higher electron antineutrino luminosity and a larger mass that
is enclosed within the gain region. The models based on the LS EOS also show a
more vigorous and aspherical downflow of accreting matter to the surface of the
protoneutron star (PNS). The accretion pattern is essential for the production
and strength of outgoing pressure waves, that can push in turn the shock to
larger radii and provide more favorable conditions for the explosion.
[abbreviated]Comment: 21 pages, 22 figures, accepted for publication in Ap
Numerical parameter survey of non-radiative black hole accretion: flow structure and variability of the rotation measure
We conduct a survey of numerical simulations to probe the structure and appearance of non-radiative black hole accretion flows like the supermassive black hole at the Galactic Centre. We find a generic set of solutions, and make specific predictions for currently feasible rotation measure (RM) observations, which are accessible to current instruments including the Expanded Very Large Array (EVLA), Giant Metrewave Radio Telescope (GMRT) and Atacama Large Millimeter Array (ALMA). The slow time variability of the RM is a key quantitative signature of this accretion flow. The time variability of RM can be used to quantitatively measure the nature of the accretion flow, and to differentiate models. Sensitive measurements of RM can be achieved using RM synthesis or using pulsars. Our energy conserving ideal magnetohydrodynamical simulations, which achieve high dynamical range by means of a deformed-mesh algorithm, stretch from several Bondi radii to about one-thousandth of that radius, and continue for tens of Bondi times. Magnetized flows which lack outward convection possess density slopes around −1, almost independent of physical parameters, and are more consistent with observational constraints than are strongly convective flows. We observe no tendency for the flows to become rotationally supported in their centres, or to develop steady outflow. We support these conclusions with formulae which encapsulate our findings in terms of physical and numerical parameters. We discuss the relation of these solutions to other approaches. The main potential uncertainties are the validity of ideal magnetohydrodynamic and the absence of a fully relativistic inner boundary condition. The RM variability predictions are testable with current and future telescope