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Author: Reuben Donald Budiardja Publisher: ISBN: Category : Languages : en Pages : 253
Book Description
This dissertation describes the current version of GenASiS and reports recent progress in its development. GenASiS is a new computational astrophysics code built for large-scale and multi-dimensional computer simulations of astrophysical phenomena, with primary emphasis on the simulations of neutron star mergers and core-collapse supernovae. Neutron star mergers are of high interest to the astrophysics community because they should be the prodigious source of gravitation waves and the most promising candidates for gravitational wave detection. Neutron star mergers are also thought to be associated with the production of short-duration, hard-spectral gamma-ray bursts, though the mechanism is not well understood. In contrast, core-collapse supernovae with massive progenitors are associated with long-duration, soft-spectral gamma-ray bursts, with the 'collapsar' hypothesis as the favored mechanism. Of equal interest is the mechanism of core-collapse supernovae themselves, which has been in the forefront of many research efforts for the better half of a century but remains a partially-solved mystery. In addition supernovae, and possibly neutron star mergers, are thought to be sites for the r-process nucleosynthesis responsible for producing many of the heavy elements. Until we have a proper understanding of these events, we will have only a limited understanding of the origin of the elements. These questions provide some of the scientific motivations and guidelines for the development of GenASiS. In this document the equations and numerical scheme for Newtonian and relativistic magnetohydrodynamics are presented. A new FFT-based parallel solver for Poisson's equation in GenASiS are described. Adaptive mesh refinement in GenASiS, and a novel way to solve Poisson's equation on a mesh with refinement based on a multigrid algorithm, are also presented. Following these descriptions, results of simulations of neutron star mergers with GenASiS such as their evolution and the gravitational wave signals and spectra that they generate are shown. In the context of core-collapse supernovae, we explore the capacity of the stationary shock instability to generate magnetic fields starting from a weak, stationary, and radial magnetic field in an initially spherically symmetric fluid configuration that models the stalled shock in the post-bounce supernova environment. Our results show that the magnetic energy can be amplified by almost 4 orders of magnitude. The amplification mechanisms for the magnetic fields are then explained.
Author: Reuben Donald Budiardja Publisher: ISBN: Category : Languages : en Pages : 253
Book Description
This dissertation describes the current version of GenASiS and reports recent progress in its development. GenASiS is a new computational astrophysics code built for large-scale and multi-dimensional computer simulations of astrophysical phenomena, with primary emphasis on the simulations of neutron star mergers and core-collapse supernovae. Neutron star mergers are of high interest to the astrophysics community because they should be the prodigious source of gravitation waves and the most promising candidates for gravitational wave detection. Neutron star mergers are also thought to be associated with the production of short-duration, hard-spectral gamma-ray bursts, though the mechanism is not well understood. In contrast, core-collapse supernovae with massive progenitors are associated with long-duration, soft-spectral gamma-ray bursts, with the 'collapsar' hypothesis as the favored mechanism. Of equal interest is the mechanism of core-collapse supernovae themselves, which has been in the forefront of many research efforts for the better half of a century but remains a partially-solved mystery. In addition supernovae, and possibly neutron star mergers, are thought to be sites for the r-process nucleosynthesis responsible for producing many of the heavy elements. Until we have a proper understanding of these events, we will have only a limited understanding of the origin of the elements. These questions provide some of the scientific motivations and guidelines for the development of GenASiS. In this document the equations and numerical scheme for Newtonian and relativistic magnetohydrodynamics are presented. A new FFT-based parallel solver for Poisson's equation in GenASiS are described. Adaptive mesh refinement in GenASiS, and a novel way to solve Poisson's equation on a mesh with refinement based on a multigrid algorithm, are also presented. Following these descriptions, results of simulations of neutron star mergers with GenASiS such as their evolution and the gravitational wave signals and spectra that they generate are shown. In the context of core-collapse supernovae, we explore the capacity of the stationary shock instability to generate magnetic fields starting from a weak, stationary, and radial magnetic field in an initially spherically symmetric fluid configuration that models the stalled shock in the post-bounce supernova environment. Our results show that the magnetic energy can be amplified by almost 4 orders of magnitude. The amplification mechanisms for the magnetic fields are then explained.
Author: Debades Bandyopadhyay Publisher: Springer Nature ISBN: 3030951715 Category : Science Languages : en Pages : 221
Book Description
This book deals with the interdisciplinary areas of nuclear physics, supernovae and neutron star physics. It addresses the physics and astrophysics of the spectacular supernova explosions, starting with the collapse of massive stars and ending with the birth of neutron stars or black holes. Recent progress in the understanding of core collapse supernova (CCSN) and observational aspects of future detections of neutrinos from CCSN explosions are discussed. The other main focus in this text is the novel phases of dense nuclear matter, its compositions and equation of state (EoS) from low to very high baryon density relevant to supernovae and neutron stars. The multi-messenger astrophysics of binary neutron star merger GW170817 and its relation to EoS through tidal deformability are also presented in detail. The synthesis of elements heavier than iron in the supernova and neutron star environment by the rapid (r)-process are treated here with special emphasis on the nucleosynthesis in the ejected material from GW170817. This monograph is written for graduate students and researchers in the field of nuclear astrophysics.
Author: Sudhanva S. Lalit Publisher: ISBN: Category : Double stars Languages : en Pages :
Book Description
The equation of state (EOS) of dense matter is a crucial input in simulations of core-collapse supernovae, evolution of neutron stars from their birth to old age and binary neutron star mergers. The EOS is required over wide ranges of density and temperature, as well as under conditions in which neutrinos are trapped, and in the presence of intense magnetic field, and rapid differential and subsequent rigid rotation. In the three research projects included in this dissertation, I have made several advances in the EOS modeling.
Author: Praveen Manoharan Publisher: Springer Nature ISBN: 3658368411 Category : Science Languages : en Pages : 77
Book Description
In the last 25 years, an extensive body of work has developed various equation of state independent - or (approximately) universal - relations that allow for the inference of neutron star parameters from gravitational wave observations. These works, however, have mostly been focused on singular neutron stars, while our observational efforts at the present, and in the near future, will be focused on binary neutron star (BNS) mergers. In light of these circumstances, the last five years have also given rise to more attempts at developing universal relations that relate BNS pre-merger neutron stars to stellar parameters of the post-merger object, mostly driven by numerical relativity simulations. In this thesis a first attempt at perturbatively deriving universal relations for binary neutron star mergers with long-lived neutron star remnants is presented. The author succeeds in confirming previous results relating pre-merger binary tidal deformabilities to the f-mode frequency of the post-merger object. Combining this result with recent advances of computing the f-mode frequency of fast rotating neutron stars, he also derives a combined relation that relates the pre-merger binary tidal deformability of a BNS to the effective compactness of a long-lived neutron star remnant. Finally, he also proposes a direct relation between these quantities with improved accuracy.
Author: Anthony Mezzacappa Publisher: World Scientific ISBN: 9812703446 Category : Science Languages : en Pages : 475
Book Description
Efforts to uncover the explosion mechanism of core collapse supernovae and to understand all of their associated phenomena have been ongoing for nearly four decades. Despite this, our theoretical understanding of these cosmic events remains limited; two- and three-dimensional modeling of these events is in its infancy. Most of the modeling efforts over the past four decades have, by necessity, been constrained to spherical symmetry, with the first two-dimensional, albeit simplified, models appearing only during the last decade. Simulations to understand the complex interplay between the turbulent stellar core fluid flow, its magnetic fields, the neutrinos produced in and emanating from the proto-neutron star, the stellar core rotation, and the strong gravitational fields have yet to be performed. Only subsets of these fundamental ingredients have been included in the models thus far, often with approximation. The purpose of this volume is to identify the outstanding issues that remain in order to come to a complete understanding of these important astrophysical events. As the book focuses on open issues rather than the current state of the art in the field OCo although the latter will certainly be discussed OCo it will remain relevant for some time."
Author: Maximilian Kölsch Publisher: ISBN: Category : Languages : de Pages : 0
Book Description
The next observing runs of advanced gravitational-wave detectors will lead to a variety of binary neutron star detections and numerous possibilities for multi-messenger observations of binary neutron star systems. In this context a clear understanding of the merger process and the possibility of prompt black hole formation after merger is important, as the amount of ejected material strongly depends on the merger dynamics. These dynamics are primarily affected by the total mass of the binary, however, the mass ratio also influences the postmerger evolution. To determine the effect of the mass ratio, we investigate the parameter space around the prompt-collapse threshold with a new set of more than 300 fully relativistic simulations, considering 165 different binary configurations. The simulations cover three equations of state and seven mass ratios in the range of 1.0≤q≤1.75, with five to seven simulations of binary systems of different total mass in each case. The threshold mass is determined through an empirical relation based on the collapse-time, which allows us to investigate effects of the mass-ratio on the threshold mass and also on the properties of the remnant system. Furthermore, we model effects of mass ratio and equation of state on tidal parameters of threshold configurations.
Author: Petr Tsatsin Publisher: ISBN: Category : Astrophysics Languages : en Pages : 110
Book Description
The starting point of any general relativistic numerical simulation is a solution of the Hamiltonian and momentum constraints that (ideally) represents an astrophysically realistic scenario. This dissertation presents a new method to produce initial data sets for binary neutron stars with arbitrary spins and orbital eccentricities. The method only provides approximate solutions to the constraints. However, it was shown that the corresponding constraint violations subside after a few orbits, becoming comparable to those found in evolutions of standard conformally flat, helically symmetric binary initial data. This dissertation presents the first spinning neutron star binary simulations in circular orbits with a orbital eccentricity less then 0.01. The initial data sets corresponding to binaries with spins aligned, zero and anti-aligned with the orbital angular momentum were evolved in time. These simulations show the orbital "hang-up" effect previously seen in binary black holes. Additionally, they show orbital eccentricities that can be up to one order of magnitude smaller than those found in helically symmetric initial sets evolutions.
Author: Tanmayee Gupte Publisher: ISBN: Category : Double stars Languages : en Pages : 0
Book Description
"The recent detection of gravitational waves (GWs) from a system of binary neutron stars (BNS) in coincidence with electromagnetic observations has launched a new era of multimessenger astrophysics. In light of the complementary knowledge to be gained through simultaneous observations, BNS mergers are one of the main targets for terrestrial GW interferometric detectors. These observations may prove critical in understanding the equation of state (EOS) of the nuclear matter inside the neutron star core, which is still poorly constrained given current observations. Understanding the neutron star (NS) EOS is critical for binary parameter estimation, and will hopefully aid in the prediction and detection of additional GW signals for systems with varying NS masses. While configurations of binary neutron stars having mass ratios far from unity are of great interest because of their potential observational signatures, generating accurate initial data for such systems has historically proven to be difficult, and relatively limited work has been done to date in simulating unequal-mass BNS because of a variety of numerical difficulties. In this work, we have modified the publicly available LORENE binary initial data code to advance our ability to construct unequal-mass BNS initial data, and used our results to initiate dynamical evolutions of BNS mergers performed using the Einstein Toolkit. We have investigated the quality of the initial data produced by our modified version of LORENE by evaluating a number of metrics, particularly the conservation of the Hamiltonian constraint when data are interpolated onto a grid for use in dynamical simulations. Here we discuss the process by which we generate initial data and use it for launching dynamical simulations, as well as our analysis of the dynamics of the merger for varying mass ratios and different EOSs represented as simple polytropes and piecewise polytropes. In particular, we analyze the relationship between the BNS mass ratio, EOS, and the ejected mass during the merger, and classify the fate of the merger remnant produced in each case."--Abstract.
Author: Reuben Donald Budiardja
Author: Reuben Donald Budiardja
Author: Debades Bandyopadhyay
Author: Sudhanva S. Lalit
Author: Praveen Manoharan
Author: Anthony Mezzacappa
Author: Maximilian Kölsch
Author: 
Author: Petr Tsatsin
Author: Brian S. Muccioli
Author: Tanmayee Gupte