Neutron Star Kick Velocities Research Articles

On the Formation of Double Neutron Stars in the Milky Way: Influence of Key Parameters

The detection of gravitational wave events has stimulated theoretical modeling of the formation and evolution of double compact objects (DCOs). However, even for the most studied isolated binary evolution channel, there exist large uncertainties in the input parameters and treatments of the binary evolution process. So far, double neutron stars (DNSs) are the only DCOs for which direct observations are available through traditional electromagnetic astronomy. In this work, we adopt a population synthesis method to investigate the formation and evolution of Galactic DNSs. We construct 324 models for the formation of Galactic DNSs, taking into account various possible combinations of critical input parameters and processes such as mass transfer efficiency, supernova type, common envelope efficiency, neutron star kick velocity, and pulsar selection effect. We employ Bayesian analysis to evaluate the adopted models by comparing with observations. We also compare the expected DNS merger rate in the galaxy with that inferred from the known Galactic population of pulsar-neutron star systems. Based on these analyses we derive the favorable range of the aforementioned key parameters.

The Jets and the Neutron Star Kick Velocity of the Supernova Remnant CTB 1

We identify jet-shaped morphology in the core-collapse supernova remnant (SNR) CTB 1 that includes two opposite structural features. We identify these as the imprints of a pair of jets that were among the last jets to explode the massive stellar progenitor of CTB 1. We find the projected angle between the jets’ axis and the direction of the pulsar velocity, which is the neutron star natal kick, to be α = 78°. We tentatively identify possible signatures of a second pair of opposite jets along a different direction. If this identification holds, SNR CTB 1 has a point-symmetric structure. The morphology and large angle of the jets’ axis to kick velocity are expected in the jittering jets explosion mechanism of core-collapse supernovae.

Lower bound for the neutrino magnetic moment from kick velocities induced at the birth of neutron stars

We show that the neutrino chirality flip, which can take place in the core of a neutron star at birth, is an efficient process to allow neutrinos to anisotropically escape, thus providing a to induce the neutron star kick velocities. The process is not subject to the no-go theorem since although the flip from left- to right-handed neutrinos happens at equilibrium, the reverse process does not take place given that right-handed neutrinos do not interact with matter and therefore detailed balance is lost. For simplicity, we model the neutron star core as being made of strange quark matter. We find that the process is efficient when the neutrino magnetic moment is not smaller than [Formula: see text], where [Formula: see text] is the Bohr magneton. When this lower bound is combined with the most stringent upper bound, which uses the luminosity data obtained from the analysis of SN 1987A, our results set a range for the neutrino magnetic moment given by [Formula: see text]. The obtained kick velocities for natal conditions are consistent with the observed ones and span the correct range of radii for typical magnetic field intensities.

Neutron star kick velocity induced by neutrino chirality flip and a lower bound for the neutrino magnetic moment

We study the neutrino chirality flip during the birth of a neutron star, produced in a core made of strange quark matter. This mechanism is applied to the neutron star kick velocity problem and we show that it is efficient when the neutrino magnetic moment is not smaller than 4.7 × 10−15μB, where μB is the Bohr magneton. When this lower bound is combined with the most stringent upper bound, our results set a range for the neutrino magnetic moment given by 4.7 × 10−15 ≤ μν/μB ≤ (0.1 − 0.4) × 10−11. The obtained kick velocities for natal conditions are consistent with the observed ones and span the correct range of radii for typical magnetic field intensities.

Dependence of gravitational wave transient rates on cosmic star formation and metallicity evolution history

ABSTRACT We compare the impacts of uncertainties in both binary population synthesis models and the cosmic star formation history on the predicted rates of gravitational wave (GW) compact binary merger events. These uncertainties cause the predicted rates of GW events to vary by up to an order of magnitude. Varying the volume-averaged star formation rate density history of the Universe causes the weakest change to our predictions, while varying the metallicity evolution has the strongest effect. Double neutron star merger rates are more sensitive to assumed neutron star kick velocity than the cosmic star formation history. Varying certain parameters affects merger rates in different ways depending on the mass of the merging compact objects; thus some of the degeneracy may be broken by looking at all the event rates rather than restricting ourselves to one class of mergers.

3D Core-Collapse Supernova Simulations: Neutron Star Kicks and Nickel Distribution

AbstractWe perform a set of neutrino-driven core-collapse supernova (CCSN) simulations studying the hydrodynamical neutron star kick mechanism in three-dimensions. Our simulations produce neutron star (NS) kick velocities in a range between ~100-600 km/s resulting mainly from the anisotropic gravitational tug by the asymmetric mass distribution behind the supernova shock. This stochastic kick mechanism suggests that a NS kick velocity of more than 1000 km/s may as well be possible. An enhanced production of heavy elements in the direction roughly opposite to the NS recoil direction is also observed as a result of the asymmetric explosion. This large scale asymmetry might be detectable and can be used to constrain the NS kick mechanism.

Theoretical support for the hydrodynamic mechanism of pulsar kicks

The collapse of a massive star's core, followed by a neutrino-driven, asymmetric supernova explosion, can naturally lead to pulsar recoils and neutron star kicks. Here, we present a two-dimensional, radiation-hydrodynamic simulation in which core collapse leads to significant acceleration of a fully-formed, nascent neutron star (NS) via an induced, neutrino-driven explosion. During the explosion, a ~10% anisotropy in the low-mass, high-velocity ejecta lead to recoil of the high-mass neutron star. At the end of our simulation, the NS has achieved a velocity of ~150 km s$^{-1}$ and is accelerating at ~350 km s$^{-2}$, but has yet to reach the ballistic regime. The recoil is due almost entirely to hydrodynamical processes, with anisotropic neutrino emission contributing less than 2% to the overall kick magnitude. Since the observed distribution of neutron star kick velocities peaks at ~300-400 km s$^{-1}$, recoil due to anisotropic core-collapse supernovae provides a natural, non-exotic mechanism with which to obtain neutron star kicks.

Direct Measurement of Neutron Star Recoil in the Oxygen‐rich Supernova Remnant Puppis A

A sequence of three Chandra X-ray Observatory High Resolution Camera images taken over a span of five years reveals arc-second-scale displacement of RX J0822-4300, the stellar remnant (presumably a neutron star) near the center of the Puppis A supernova remnant. We measure its proper motion to be 0.165+/-0.025 arcsec/yr toward the west-southwest. At a distance of 2 kpc, this corresponds to a transverse space velocity of ~1600 km/s. The space velocity is consistent with the explosion center inferred from proper motions of the oxygen-rich optical filaments, and confirms the idea that Puppis A resulted from an asymmetric explosion accompanied by a kick that imparted roughly 3*10^49 ergs of kinetic energy (some 3 percent of the kinetic energy for a typical supernova) to the stellar remnant. We discuss constraints on core-collapse supernova models that have been proposed to explain neutron star kick velocities.

Gamma‐Ray Bursts from High‐Velocity Neutron Stars

We investigate the viability of Galactic corona models of gamma-ray bursts by calculating the spatial distribution expected for a population of high-velocity neutron stars born in the Galactic disk and moving in a gravitational potential that includes contributions from the bulge, disk, and dark matter halo of our Galaxy and also from these same components of our neighboring galaxy M31. We consider two classes of models: one in which the bursts radiate isotropically and one in which the bursts are beamed. We place constraints on these models by comparing the expected brightness and angular distributions with the data in the BATSE 3B catalog. We find that if the bursts radiate isotropically, then the Galactic corona model can reproduce the BATSE peak flux and angular distributions for neutron star kick velocities vkick 800 km s-1, source turn-on ages ton 20 Myr, and BATSE sampling distances 130 kpc dmax 350 kpc. If the bursts are instead beamed with an opening half-angle ?b, no turn-on age is required, and the model can reproduce the BATSE data for 15? ?b 20? and 80 kpc dmax 250 kpc.

On detection of gamma-ray bursts from Andromeda

If gamma-ray bursts originate in a corona of high velocity neutron star around the Milky Way, it should also be possible to detect them from a similar corona around Andromeda. Adopting a simple model of such a corona, we evaluate the ability of instruments on existing and on some proposed missions to detect an excess of bursts toward Andromeda. We investigate the optimal properties of an instrument designed to detect such an excess. We find that if the bursts radiate isotropically, an experiment with a sampling distance d max > 600 kpc is required in order to detect the expected excess of bursts in the direction of Andromeda in ≈ 1 year of observation. If the bursts are beamed forward and backward along the direction of the neutron star's kick velocity, an experiment with d max > 800 kpc is required in order to detect the expected excess in a similar amount of time. Detection of an excess of bursts toward Andromeda would constitute definitive evidence that the bursts are Galactic in origin. Conversely, the observation of no excess toward Andromeda would strongly suggest that the bursts are cosmological in origin, provided that the observation is made by an instrument at least orders of magnitude more sensitive than BATSE, given current constraints on the BATSE sampling distance.

Gamma-ray bursts from high velocity neutron stars

We investigate the viability of the Galactic corona model of γ-ray bursts by calculating the spatial distribution of neutron stars born with high velocities in the Galactic disk, and comparing the resulting brightness and angular distribution with the BATSE data. We find that the Galactic corona model can reproduce the BATSE peak flux and angular distribution data for neutron star kick velocities ≳ 800 km s−1, source turn-on ages ≳ 10 Myrs, and sampling depths 100 kpc ≲d max≲ 400 kpc.