73 research outputs found
Neutrino Flavor Evolution in Binary Neutron Star Merger Remnants
We study the neutrino flavor evolution in the neutrino-driven wind from a
binary neutron star merger remnant consisting of a massive neutron star
surrounded by an accretion disk. With the neutrino emission characteristics and
the hydrodynamical profile of the remnant consistently extracted from a
three-dimensional simulation, we compute the flavor evolution by taking into
account neutrino coherent forward scattering off ordinary matter and neutrinos
themselves. We employ a "single-trajectory" approach to investigate the
dependence of the flavor evolution on the neutrino emission location and angle.
We also show that the flavor conversion in the merger remnant can affect the
(anti-)neutrino absorption rates on free nucleons and may thus impact the
-process nucleosynthesis in the wind. We discuss the sensitivity of such
results on the change of neutrino emission characteristics, also from different
neutron star merger simulations.Comment: 24 pages, 20 figures. Figures and text in the result section V have
been modified (due to a numerical error), conclusion remain
Gravitational-wave luminosity of binary neutron stars mergers
We study the gravitational-wave peak luminosity and radiated energy of
quasicircular neutron star mergers using a large sample of numerical relativity
simulations with different binary parameters and input physics. The peak
luminosity for all the binaries can be described in terms of the mass ratio and
of the leading-order post-Newtonian tidal parameter solely. The mergers
resulting in a prompt collapse to black hole have largest peak luminosities.
However, the largest amount of energy per unit mass is radiated by mergers that
produce a hypermassive neutron star or a massive neutron star remnant. We
quantify the gravitational-wave luminosity of binary neutron star merger
events, and set upper limits on the radiated energy and the remnant angular
momentum from these events. We find that there is an empirical universal
relation connecting the total gravitational radiation and the angular momentum
of the remnant. Our results constrain the final spin of the remnant black-hole
and also indicate that stable neutron star remnant forms with super-Keplerian
angular momentum.Comment: 5 pages, 4 figure
Thermodynamics conditions of matter in neutron star mergers
Matter in neutron star collisions can reach densities up to few times the
nuclear saturation threshold and temperatures up to one hundred MeV.
Understanding the structure and composition of such matter requires many-body
nonperturbative calculations that are currently highly uncertain.Unique
constraints on the neutron star matter are provided by gravitational-wave
observations aided by numerical relativity simulations. In this work, we
explore the thermodynamical conditions of matter and radiation along the merger
dynamics. We consider 3 microphysical equation of state models and numerical
relativity simulations including an approximate neutrino transport scheme. The
neutron star cores collision and their multiple centrifugal bounces heat the
initially cold matter to several tens of MeV. Streams of hot matter with
initial densities move outwards and cool due to decompression
and neutrino emission. The merger can result in a neutron star remnant with
densities up to and temperatures ~MeV. The highest
temperatures are confined in an approximately spherical annulus at densities
. Such temperatures favour positron-neutron capture at densities
, thus leading to a neutrino emission dominated by electron
antineutrinos. We study the impact of trapped neutrinos on the remnant matter's
pressure, electron fraction and temperature and find that it has a negligible
effect. Disks around neutron star or black hole remnant are neutron rich and
not isentropic, but they differ in size, entropy and lepton fraction depending
on the nature of the central object. In presence of a black hole, disks are
smaller and mostly transparent to neutrinos; in presence of a massive neutron
star, they are more massive, geometrically and optically thick.Comment: 23 pages, 10 Figures, to be submitted to EPJA Topical Issue: The
first Neutron Star Merger Observation - Implications for Nuclear Physics.
Movies of the thermodynamical conditions available also on the youtube
channel https://www.youtube.com/channel/UChmn-JGNa9mfY5H5938jni
Neutrino-driven winds in the aftermath of a neutron star merger: nucleosynthesis and electromagnetic transients
We present a comprehensive nucleosynthesis study of the neutrino-driven wind
in the aftermath of a binary neutron star merger. Our focus is the initial
remnant phase when a massive central neutron star is present. Using tracers
from a recent hydrodynamical simulation, we determine total masses and
integrated abundances to characterize the composition of unbound matter. We
find that the nucleosynthetic yields depend sensitively on both the life time
of the massive neutron star and the polar angle. Matter in excess of up to becomes unbound until . Due to
electron fractions of mainly nuclei with mass
numbers are synthesized, complementing the yields from the earlier
dynamic ejecta. Mixing scenarios with these two types of ejecta can explain the
abundance pattern in r-process enriched metal-poor stars. Additionally, we
calculate heating rates for the decay of the freshly produced radioactive
isotopes. The resulting light curve peaks in the blue band after about . Furthermore, high opacities due to heavy r-process nuclei in the dynamic
ejecta lead to a second peak in the infrared after .Comment: 15 pages, 18 figures, 2 tables, accepted by Ap
- …