165 research outputs found
Constraint on the maximum mass of neutron stars using GW170817 event
We revisit the constraint on the maximum mass of cold spherical neutron stars
coming from the observational results of GW170817. We develop a new framework
for the analysis by employing both energy and angular momentum conservation
laws as well as solid results of latest numerical-relativity simulations and of
neutron stars in equilibrium. The new analysis shows that the maximum mass of
cold spherical neutron stars can be only weakly constrained as M_{\rm max}
\alt 2.3M_\odot. Our present result illustrates that the merger remnant
neutron star at the onset of collapse to a black hole is not necessarily
rapidly rotating and shows that we have to take into account the angular
momentum conservation law to impose the constraint on the maximum mass of
neutron stars.Comment: 14 pages, 5 figures, matches the version accepted by PRD for
publicatio
Enrichment of Jupiter’s Atmosphere by Late Planetesimal Bombardment
Jupiter’s atmosphere is enriched with heavy elements by a factor of about 3 compared to a protosolar composition. The origin of this enrichment and whether it represents the bulk composition of the planetary envelope remain unknown. Internal structure models of Jupiter suggest that its envelope is separated from the deep interior and that the planet is not fully mixed. This implies that Jupiter’s atmosphere was enriched with heavy elements just before the end of its formation. Such enrichment can be a result of late planetesimal accretion. However, in situ Jupiter formation models suggest a decreasing accretion rate with increasing planetary mass, which cannot explain Jupiter’s atmospheric enrichment. In this study, we model Jupiter’s formation and show that the migration of proto-Jupiter from ∼20 au to its current location can lead to late planetesimal accretion and atmospheric enrichment. Late planetesimal accretion does not occur if proto-Jupiter migrates only a few astronomical units. We suggest that if Jupiter’s outermost layer is fully mixed and is relatively thin (up to ∼20% of its mass), such late accretion can explain its measured atmospheric composition. It is therefore possible that Jupiter underwent significant orbital migration followed by late planetesimal accretion
Mass Ejection from the Remnant of a Binary Neutron Star Merger: Viscous-Radiation Hydrodynamics Study
We perform long-term general relativistic neutrino radiation hydrodynamics
simulations (in axisymmetry) for a massive neutron star (MNS) surrounded by a
torus, which is a canonical remnant formed after the binary neutron star
merger. We take into account the effects of viscosity, which is likely to arise
in the merger remnant due to magnetohydrodynamical turbulence. As the initial
condition, we employ the azimuthally averaged data of the MNS-torus system
derived in a three-dimensional, numerical-relativity simulation for the binary
neutron star merger. The viscous effect plays key roles for the remnant
evolution and mass ejection from it in two phases of the evolution. In the
first ms, a differential rotation state of the MNS is changed to
a rigidly rotating state, and as a result, a sound wave, which subsequently
becomes a shock wave, is formed in the vicinity of the MNS due to the variation
of the quasi-equilibrium state of the MNS. The shock wave induces significant
mass ejection of mass for the alpha
viscosity parameter of . For the longer-term evolution with s, a significant fraction of the torus material is ejected. The ejecta
mass is likely to be of order , so that the total mass of the
viscosity-driven ejecta could dominate that of the dynamical ejecta of mass
. The electron fraction, , of the ejecta is
always high enough () that this post-merger ejecta is
lanthanide-poor; hence, the opacity of the ejecta is likely to be
times lower than that of the dynamical ejecta. This indicates that the
electromagnetic signal from the ejecta would be rapidly evolving, bright, and
blue if it is observed from a small viewing angle () for
which the effect of the dynamical ejecta is minor.Comment: 21 pages, 18 figures, accepted for publication in Ap
A Monte-Carlo based relativistic radiation hydrodynamics code with a higher-order scheme
We develop a new relativistic radiation hydrodynamics code based on the
Monte-Carlo algorithm. In this code, we implement a new scheme to achieve the
second-order accuracy in time in the limit of a large packet number for solving
the interaction between matter and radiation. This higher-order time
integration scheme is implemented in the manner to guarantee the
energy-momentum conservation to the precision of the geodesic integrator. The
spatial dependence of radiative processes, such as the packet propagation,
emission, absorption, and scattering, are also taken into account up to the
second-order accuracy. We validate our code by solving various test-problems
following the previous studies; one-zone thermalization, dynamical diffusion,
radiation dragging, radiation mediated shock-tube, shock-tube in the optically
thick limit, and Eddington limit problems. We show that our code reproduces
physically appropriate results with reasonable accuracy and also demonstrate
that the second-order accuracy in time and space is indeed achieved with our
implementation for one-zone and one-dimensional problems.Comment: 25 pages, 10 figures, submitted to PR
Collapse of rotating massive stars leading to black hole formation and energetic supernovae
We explore a possible scenario of the explosion as a result of core collapses
of rotating massive stars that leave a black hole by performing a
radiation-viscous-hydrodynamics simulation in numerical relativity. We take
moderately and rapidly rotating compact pre-collapse stellar models derived in
stellar evolution calculations as the initial conditions. We find that the
viscous heating in the disk formed around the central black hole powers an
outflow. For rapidly rotating models, the explosion energy is erg, which is comparable to or larger than that of typical
stripped-envelope supernovae, indicating that a fraction of such supernovae may
be explosions powered by black-hole accretion disks. The explosion energy is
still increasing at the end of the simulations with a rate of erg/s,
and thus, it may reach erg. The nucleosynthesis calculation shows
that the mass of Ni amounts to , which, together
with the high explosion energy, satisfies the required amount for broad-lined
type Ic supernovae. The moderately rotating models predict small ejecta mass of
order and explosion energy of erg. Due to the
small ejecta mass, these models may predict a short-timescale transient with
the rise time 35 d. It can lead to a bright ( erg/s) transient
like superluminous supernovae in the presence of dense massive circum-stellar
medium. Irrespective of the models, the lowest value of the electron fraction
of the ejecta is , and thus, the synthesis of heavy -process
elements is not found in our calculation.Comment: 23 pages, 11 figures, accepted for publication in Ap
Properties of neutrino transfer in a deformed remnant of neutron star merger
We study properties of neutrino transfer in a remnant of neutron star merger,
consisting of a massive neutron star and a surrounding torus. We perform
numerical simulations of the neutrino transfer by solving the Boltzmann
equation with momentum-space angles and energies of neutrinos for snapshots of
the merger remnant having elongated shapes. The evaluation of the neutrino
distributions in the multi-dimensions enable us to provide the detailed
information of angle and energy spectra and neutrino reaction rates. We
demonstrate features of asymmetric neutrino fluxes from the deformed remnant
and investigate the neutrino emission region by determining the neutrinosphere
for each energy. We examine the emission and absorption of neutrinos to
identify important ingredients of heating rates through neutrino irradiation.
We show that the contributions of - and -types neutrinos are
important for the heating in the region above the massive neutron star. We also
examine the angle moments and the Eddington tensor calculated directly by the
neutrino distribution functions and compare them with those obtained by a
moment closure approach, which is often used in the study of neutrino-radiation
hydrodynamics. We show that the components of the Eddington tensor have
non-monotonic behaviors and the approximation of the closure relation may
become inaccurate for high energy neutrinos, whose fluxes are highly aspherical
due to the extended merger remnant.Comment: 28 pages, 33 figures, revised version accepted for publication in Ap
Supernova-like explosion of massive rotating stars from disks surrounding a black hole
We perform a new general-relativistic viscous-radiation hydrodynamics
simulation for supernova-like explosion associated with stellar core collapse
of rotating massive stars to a system of a black hole and a massive torus
paying particular attention to large-mass progenitor stars with the zero-age
main-sequence mass of 20, 35, and 45 of
Ref.~\cite{Aguilera-Dena2020oct}. Assuming that a black hole is formed in a
short timescale after the onset of the stellar collapse, the new simulations
are started from initial data of a spinning black hole and infalling matter
that self-consistently satisfy the constraint equations of general relativity.
It is found that with a reasonable size of the viscous parameter, the
supernova-like explosion is driven by the viscous heating effect in the torus
around the black hole irrespective of the progenitor mass. The typical
explosion energy and ejecta mass for the large-mass cases (
and ) are erg and , respectively, with
Ni mass larger than . These are consistent with the
observational data of stripped-envelope and high-energy supernovae such as
broad-lined type Ic supernovae. This indicates that rotating stellar collapses
of massive stars to a black hole surrounded by a massive torus can be a central
engine for high-energy supernovae. By artificially varying the angular velocity
of the initial data, we explore the dependence of the explosion energy and
ejecta mass on the initial angular momentum and find that the large explosion
energy erg and large Ni mass are
possible only when a large-mass compact torus with mass is
formed.Comment: 20 pages, 11 figures, submitted to PR
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