574 research outputs found
Muons in the aftermath of neutron star mergers and their impact on trapped neutrinos
No full textIn the upcoming years, present and next-generation gravitational wave
observatories will detect a larger number of binary neutron star (BNS) mergers
with increasing accuracy. In this context, improving BNS merger numerical
simulations is crucial to correctly interpret the data and constrain the
equation of state (EOS) of neutron stars (NSs). State-of-the-art simulations of
BNS mergers do not include muons. However, muons are known to be relevant in
the microphysics of cold NSs and are expected to have a significant role in
mergers, where the typical thermodynamic conditions favour their production.
Our work is aimed at investigating the impact of muons on the merger remnant.
We post-process the outcome of four numerical relativity simulations of BNS
mergers performed with three different baryonic EOSs and two mass ratios
considering the first milliseconds after merger. We compute the abundance
of muons in the remnant and analyse how muons affect the trapped neutrino
component and the fluid pressure. We find that depending on the baryonic EOS,
the net fraction of muons is between and the net fraction of
electrons. Muons change the flavour hierarchy of trapped (anti-)neutrinos such
that deep inside the remnant, muon anti-neutrinos are the most abundant,
followed by electron anti-neutrinos. Finally, muons and trapped neutrinos
modify the neutron-to-proton ratio, affecting the remnant pressure by up to
when compared with calculations neglecting them. This work demonstrates
that muons have a non-negligible effect on the outcome of BNS merger
simulations, and they should be included to improve the accuracy of a
simulation.Comment: 19 pages, 11 figure
Optimization of Finite-Differencing Kernels for Numerical Relativity Applications
No full textA simple optimization strategy for the computation of 3D finite-differencing kernels on many-cores architectures is proposed. The 3D finite-differencing computation is split direction-by-direction and exploits two level of parallelism: in-core vectorization and multi-threads shared-memory parallelization. The main application of this method is to accelerate the high-order stencil computations in numerical relativity codes. Our proposed method provides substantial speedup in computations involving tensor contractions and 3D stencil calculations on different processor microarchitectures, including Intel Knight Landing
Optimization of Finite-Differencing Kernels for Numerical Relativity Applications
No full textA simple optimization strategy for the computation of 3D finite-differencing kernels on many-cores architectures is proposed. The 3D finite-differencing computation is split direction-by-direction and exploits two level of parallelism: in-core vectorization and multi-threads shared-memory parallelization. The main application of this method is to accelerate the high-order stencil computations in numerical relativity codes
Neutrino treatment in multidimensional astrophysical simulations : a new spectral scheme
No full textNeutrinos play a central role in modern physics and astrophysics. Their extremely weak interaction
rate with baryons and other leptons makes their detection on the Earth difficult and challenging.
At the same time, it implies that the emission and the absorption of neutrinos are the dominant
radiative processes in hot and dense astrophysical environment (such as core-collapse supernovae
and the merger of binary compact objects), where photons are completely trapped and diffuse out on
much longer timescales. The implementation of neutrino-transport schemes in hydrodynamics simulations
is a subtle problem, especially in multi-dimensions, where an accurate solution of the transport
equations can be, computationally speaking, extremely expensive.
In this work, we have developed a new approximate neutrino-radiation treatment, the Advanced Spectral
Leakage (ASL) scheme; after having tested and calibrated it, we have shown a variety of applications,
both in the context of core-collapse supernovae and of binary neutron star mergers.
The ASL scheme was derived from previous grey leakage schemes, and it retains the conceptual and the
computational simplicity that characterize leakage schemes. Different from its predecessors, the new
treatment is spectral (i.e. it retains information on the particle energy), and it includes the modeling
of a neutrino trapped component in optically thick conditions and of neutrino absorption terms in
optically thin conditions. The scheme has been tested against detailed neutrino-transport in the context
of spherically symmetric models of collapsing stellar cores. We have shown that it is able to capture,
with reasonable accuracy, the main expected features during the collapse phase, at core bounce and in the
first hundreds of millisecond after bounce, both for the fundamental hydrodynamics and neutrino quantities.
The optical depth is a central quantity in leakages schemes. We have also developed a new algorithm to
compute the optical depth in multi-dimensional domains, without any symmetry constraint.
We called it Multidimensional Optical Depth Algorithm (MODA).
The major application of the ASL scheme in this work has been the study of the development of a neutrino-driven
wind from the hot and dense disc resulting from the merger of two neutron star. This process has been studied
for the first time in 3D Cartesian simulations, performed with the FISH code. The intense (10^53 erg/s) neutrino
emission coming from the (probably, unstable) hyper massive neutron star and from the disc itself is partially
re-absorbed by low density (< 10^10 g/cm^3), neutron-rich (Y_e < 0.1) matter inside disc. This energy deposition
drives a baryonic wind, mainly perpendicular to the disc plane, on a timescale of ~50 ms. Neutrino-matter
interactions in the wind modify significantly the electron fraction of matter: the resulting distribution shows
a broad range of Y_e, from 0.2 to 0.4, with larger values along the polar directions than along the equatorial one.
At ~100ms after the merger, the amount of ejecta is of the order of 2% the initial mass of the disc, thus it
represents a significant channel for mass ejection from binary neutron star mergers. The broad range in Y_e represents
an interesting signature in the context of r-process nucleosynthesis.
Furthermore, we have shown other applications of the ASL scheme.
First, we have implemented it in the MHD version of the FISH code to study the electron fraction in jets resulting from
magneto-rotationally driven supernovae. In the case of strong and fast jet formation (~30 ms after core bounce),
the electron fraction in the ejecta is low enough (Y_e < 0.3) to produce robust r-process nucleosynthesis.
Second, we have implemented the ASL scheme inside the SPH code SPHYNCS, to perform core-collapse simulations.
The results we have obtained are compatible with what we have obtained with grid codes. This model shows that the
scheme is of easy implementation also in Lagrangian, multidimensional SPH codes.
Finally, we have designed a new prescription to explode artificially spherically symmetric core-collapse models,
using the IDSA scheme for electron neutrinos and the ASL scheme for mu and tau neutrinos. The extra energy deposition
required to trigger the explosion is obtained by the parametrized absorption of heavy flavour neutrinos inside the
gain region. The model has shown promising results and it is well suited to study the explosive nucleosynthesis for
broad stellar progenitor samples, including detailed neutrino treatment
Neutrino emission from binary neutron star mergers: characterizing light curves and mean energies
No full textNeutrinos are copiously emitted by neutron star mergers, due to the high
temperatures reached by dense matter during the merger and its aftermath.
Neutrinos influence the merger dynamics and shape the properties of the ejecta,
including the resulting -process nucleosynthesis and kilonova emission. In
this work, we analyze neutrino emission from a large sample of merger radiation
hydrodynamics simulations in Numerical Relativity, covering a broad range of
initial masses, nuclear equation of state and viscosity treatments. We extract
neutrino luminosities and mean energies, and compute quantities of interest
such as the peak values, peak broadnesses, time averages and decrease time
scales. We provide a systematic description of such quantities, including their
dependence on the initial parameters of the system. We find that for equal-mass
systems the total neutrino luminosity (several )
decreases for increasing reduced tidal deformability, as a consequence of the
less violent merger dynamics. Similarly, tidal disruption in asymmetric mergers
leads to systematically smaller luminosities. Peak luminosities can be twice as
large as the average ones. Electron antineutrino luminosities dominate
(initially by a factor of 2-3) over electron neutrino ones, while electron
neutrinos and heavy flavour neutrinos have similar luminosities. Mean energies
are nearly constant in time and independent on the binary parameters. Their
values reflect the different decoupling temperature inside the merger remnant.
Despite present uncertainties in neutrino modelling, our results provide a
broad and physically grounded characterization of neutrino emission, and they
can serve as a reference point to develop more sophisticated neutrino transport
schemes.Comment: 30 pages, 14 figures, 4 Tables, published in EPJ A topical issue
"CompOSE: a repository for Neutron Star Equations of State and Transport
Properties
AT2017gfo: Bayesian inference and model selection of multicomponent kilonovae and constraints on the neutron star equation of state
No full textThe joint detection of the gravitational wave GW170817, of the short gamma-ray burst GRB170817A and of the kilonova AT2017gfo, generated by the the binary neutron star (NS) merger observed on 2017 August 17, is a milestone in multimessenger astronomy and provides new constraints on the NS equation of state. We perform Bayesian inference and model selection on AT2017gfo using semi-analytical, multicomponents models that also account for non-spherical ejecta. Observational data favour anisotropic geometries to spherically symmetric profiles, with a log-Bayes' factor of similar to 10(4), and favour multicomponent models against single-component ones. The best-fitting model is an anisotropic three-component composed of dynamical ejecta plus neutrino and viscous winds. Using the dynamical ejecta parameters inferred from the best-fitting model and numerical-relativity relations connecting the ejecta properties to the binary properties, we constrain the binary mass ratio to q < 1.54 and the reduced tidal parameter to . Finally, we combine the predictions from AT2017gfo with those from GW170817, constraining the radius of a NS of 1.4 M-circle dot to 12.2 +/- 0.5 km (1 sigma level). This prediction could be further strengthened by improving kilonova models with numerical-relativity information
Kejahatan HAM Ras Albino Di Afrika
No full textHuman rights recognize forms of violation and crime, discrimination against something different is one form of violation of human rights. Africa is a large country and has many differences and gatherings of many ethnic groups and religions, it does not rule out the possibility of a conflict. In this case the albino group is often discriminated against, persecuted, bullied, raped and even killed. Ranging from babies to adults. On the basis of the background that has been written, the author will put forward a discussion about the form of what kind of human rights violations against Albino people in Africa. The method used in this journal is the Juridical Normative Method. The author uses the Juridical Normative Method to be able to find out directly in order to be able to examine how the application of the specific laws of existing international conventions about human rights violations. The results of this material discussion found that many human rights crimes were committed because of the negative stigma and myths about how albino people exist and albino people have high selling prices for spiritual needs for shamans in Africa and the black market. Discrimination against Albino people is often done even after they are born until they grow up, starting from being isolated from the surrounding environment, having difficulty getting the right to learn, the difficulty of getting the right to work, and feeling threatened if they are outside their hiding place. murder, rape, and even mutilation often occur in their lives
Probing the incompressibility of nuclear matter at ultra-high density through the prompt collapse of asymmetric neutron star binaries
No full textUsing 250 neutron star merger simulations with microphysics, we explore for
the first time the role of nuclear incompressibility in the prompt collapse
threshold for binaries with different mass ratios. We demonstrate that
observations of prompt collapse thresholds, either from binaries with two
different mass ratios or with one mass ratio but combined with the knowledge of
the maximum neutron star mass or compactness, will constrain the
incompressibility at the maximum neutron star density, , to within
tens of percent. This, otherwise inaccessible, measure of can
potentially reveal the presence of hyperons or quarks inside neutron stars.Comment: 7 pages, 4 figures; 2 tables and 4 figures in the appendi
Numerical Relativity Simulations of the Neutron Star Merger GW170817: Long-term Remnant Evolutions, Winds, Remnant Disks, and Nucleosynthesis
No full textThe Wind and the Sun in Ninam ISO shb
No full textThe narrative of the wind and the sun by Albino Xiriana, a native speaker of the Ninam language, Northern dialect (ISO shb, Yanomami family, spoken in the Uraricaa river in Brazil and the Paragua river in Venezuela). Data was recorded in 2017 in the Saúba village in the Uraricaa river. Albino was told the story twice and retold it to the recorder only once. Thiago Chacon was the author of the recording and both transcribed the story with Ninam's orthography and translated it into portuguese.
Ninam graphemes that diverge from IPA and their equivalents in IPA:
ë = ə
x = ʃ
tx = tʃ
th = tʰ
VV = Vʔ
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