Dissertations / Theses on the topic 'Neutron stars'
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1
Cernohorsky, Jan. "Neutrino driven neutron star formation." Amsterdam : Amsterdam : Rodopi ; Universiteit van Amsterdam [Host], 1990. http://dare.uva.nl/document/91884.
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Roark, Jacob Brian. "The Deconfinement Phase Transition in Neutron Stars and Proto-Neutron Stars." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1542979864566784.
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Naso, Luca. "Magnetic Fields in Proto-Neutron Stars and in Accretion Discs Around Neutron Stars." Doctoral thesis, SISSA, 2009. http://hdl.handle.net/20.500.11767/4267.
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Themain characters of this thesis are themagnetic field, the plasma velocity field, the turbulentmagnetic
resistivity and the numerical codes. They act on two different stages and
on two different levels and occasionaly there are other bit players, e.g. the α-effect, the
quenching, the differential rotation, themagnetic streamfunction, themagnetic Reynolds
number, the Interactive Data Language and even ZEUS. All of them are led by the same
invisible hand with the purpose of understanding better the intricate topic of the magnetic
field - plasma relation.
The two stages of the scene could not be more different, in one case everything is done
in less than a minute inside a proto-neutron star soon after a supernova explosion, in the
other case there is no time evolution at all and an equilibrium configuration is looked for
inside a disc ofmatter spiraling around a neutron star. Nevertheless the same set of equations
can describe the behaviour of the characters on both stages, this set is composed of
the equations of the electromagnetic field plus the fluid equations.
However knowing that the answers to all of your questions are written inside only
one book, does not mean that you are able to read that book ... It is at this moment that
the numerical codes come into the scene, offering you a way of translating the book in
a language that you know. Unfortunately they like playing tricks and you cannot trust
their translations unless you take many precautions every time.
Eventually, after the equations have been solved, comes the art of interpreting the results;
a task that might seem quite simple in comparison with the difficulties overcome
on the path to get there, but that requires a deep knowledge of what has already been
done and a good intuition about what can possibly happen later on.
We do not presume to have made big leaps forward in the process of understanding
the behaviour of the magnetic field in the cases considered here, nonetheless thanks to
our simplified models we were able to grasp the fundamental aspects of the phenomena
being considered, to gain some insights and to propose new falsifiable ideas. At the
same time we have also developed new tools for making our models more elaborate and
realistic. Therefore we expect to find even more characters in the future Chapters of this analysis, but that is another story, and will be told another time.
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Riz, Luca. "Spin polarization effects in neutron stars." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/253498.
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This thesis is concerned with effects of spin polarization in neutron stars. In particular, we focus on static and dynamic properties of dense neutron matter. We use two different kind of potential to perform our studies: the phenomenological two-body Argonne V$8$' potential plus the three-body Urbana IX force and a modern local version of chiral effective potential up to next-to-next-to-leading order (N$2$LO).
Estimates are calculated for the neutrino mean free path in partially spin-polarized neutron matter starting from Quantum Monte Carlo (QMC) simulations and using mean-field approaches to compute the response function in the longitudinal and transverse channel. We also compute magnetic susceptibility of dense neutron matter from accurate QMC calculations of partially spin-polarized systems. Twist-averaged boundary conditions (TABC) have been implemented to reduce finite-size effects. In the results, we also account for the theoretical uncertainty coming from the chiral expansion scheme.
These results may play a role in studying high-energy phenomena such as neutron star mergers and supernova explosions, although they have been computed only at T$=0$ K.
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Riz, Luca. "Spin polarization effects in neutron stars." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/253498.
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This thesis is concerned with effects of spin polarization in neutron stars. In particular, we focus on static and dynamic properties of dense neutron matter. We use two different kind of potential to perform our studies: the phenomenological two-body Argonne V$8$' potential plus the three-body Urbana IX force and a modern local version of chiral effective potential up to next-to-next-to-leading order (N$2$LO).
Estimates are calculated for the neutrino mean free path in partially spin-polarized neutron matter starting from Quantum Monte Carlo (QMC) simulations and using mean-field approaches to compute the response function in the longitudinal and transverse channel. We also compute magnetic susceptibility of dense neutron matter from accurate QMC calculations of partially spin-polarized systems. Twist-averaged boundary conditions (TABC) have been implemented to reduce finite-size effects. In the results, we also account for the theoretical uncertainty coming from the chiral expansion scheme.
These results may play a role in studying high-energy phenomena such as neutron star mergers and supernova explosions, although they have been computed only at T$=0$ K.
6
Tang, Pui-shan Anisia. "The physics of neutron stars." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B38297036.
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Tang, Pui-shan Anisia, and 鄧珮姗. "The physics of neutron stars." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B38297036.
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Viganò, Daniele. "Magnetic fields in neutron stars." Doctoral thesis, Universidad de Alicante, 2013. http://hdl.handle.net/10045/36185.
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González, Boquera Claudia. "Neutron-rich matter in atomic nuclei and neutron stars." Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/668774.
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The proper understanding of the equation of state (EoS) of highly asymmetric nuclear matter is essential when studying systems such as neutron stars (NSs). Using zero-range Skyrme interactions and finite-range interactions such as Gogny forces, momentum-dependent interactions (MDI) and simple effective interactions (SEI), we analyze the properties of the EoS and the influence they may have on the calculations for NSs.
We start by studying the convergence properties of the Taylor series expansion of EoS in powers of the isospin asymmetry. Next, we analyze the accuracy of the results for β-stable nuclear matter, which is found in the interior of NSs, when it is computed using the Taylor expansion of the EoS. The agreement with the results obtained using the full expression of the EoS is better for interactions with small-to-moderate values of the slope of the symmetry energy L.
The mass and radius relation for a NS is obtained by integrating the so-called Tolman-Oppenheimer-Volkoff (TOV) equations, where the input is the EoS of the system. We have studied the mass-radius relation for Skyrme and Gogny interactions, and we see that that very soft forces are not able to give stable solutions of the TOV equations and only the stiff enough parametrizations can provide 2M0 NSs. We also notice that none of the existing parametrizations of the standard Gogny D1 interaction is able to provide a NS inside the observational constraints. Because of that, we propose a new parametrization, which we name D1M∗, that is able to provide NSs of 2M0 while still providing the same good description of finite nuclei as D1M. A parametrization D1M∗∗ is also presented, which is fitted in the same way as D1M∗ and provides NSs up to 1.91M0.
Moreover, we estimate the core-crust transition in NSs by finding where the nuclear matter in the core is unstable against fluctuations of the density. To do that, we employ two methods, the thermodynamical method and the dynamical method. In the case of finite-range interactions, such as the Gogny ones, to use the dynamical method we have had to derive the explicit expression of the energy curvature matrix in momentum space for this type of interactions. We observe a decreasing trend of the transition density with the slope L of the symmetry energy, while the correlation between the transition pressure and L is much lower.
Finally different NS properties are studied. The crustal properties, such as the crustal mass, crustal thickness and crustal fraction of the moment of inertial have lower values if one computes them using the core-crust transition density obtained with the dynamical method instead of the one obtained with the thermodynamical method, pointing out the importance of the accurate evaluation of the transition density when studying observational phenomena. We have also studied the moment of inertia of NSs, which is compared to constraints proposed in the literature. Finally, the tidal deformability for NSs is also calculated and compared with the constraints coming from the GW170817 event detected by the LIGO and Virgo observatories and which accounts for the merger of two NSs in a binary system.El coneixement de l’equació d’estat (EoS) de matèria altament densa i assimètrica és essencial per tal d’estudiar les estrelles de neutrons (NSs). En aquesta tesi s’analitzen, utilitzant interaccions de camp mig no relativistes, les propietats de l’EoS i la seva influència en càlculs de NSs. Primerament, s’estudia la convergència del desenvolupament en sèrie de Taylor de l’EoS en potències de l'assimetria d’isospí. Seguidament, s’analitza l’exactitud dels resultats per matèria β-estable, la qual es troba a l’interior de les NSs, quan es calcula utilitzant el desenvolupament de Taylor de l’EoS. La relació entre la massa i el radi obtinguda integrant les equacions Tolman-Oppenheimer-Volkoff (TOV) també és estudiada. A causa de que les interaccions de Gogny de la família D1 no aconsegueixen donar NSs compatibles amb observacions astrofísiques, en aquesta tesi proposem dues noves forces de Gogny, anomenades D1M∗ i D1M∗∗, les quals poden donar, respectivament, NSs de 2 i 1.91 masses solars. Una altra part de la tesi es dedica a l’estudi de la transició entre l’escorça i el nucli, buscant la densitat a la qual la matèria uniforme al nucli és inestable contra fluctuacions de densitat. Ho estudiem amb dos mètodes, el mètode termodinàmic i el mètode dinàmic. Finalment, s’analitzen diverses propietats de les NSs, com són la relació entre la massa i el radi de l’estrella, les propietats de l’escorça, el moment d’inèrcia, així com la deformació deguda als corrents de marea (tidal deformability) que està relacionada amb l’emissió d’ones gravitacionals en sistemes binaris d’estrelles de neutrons.
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Thurman, Hugh O. Copeland Gary E. "Neutron star electromagnetic field structure /." Connect to this resource. (Authorized users only), 2004.
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Harko, Tiberiu. "Properties of strange stars." Thesis, Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk:8888/cgi-bin/hkuto%5Ftoc%5Fpdf?B23242280.
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Straaten, Steve van. "Timing similarities among accreting neutron stars." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2004. http://dare.uva.nl/document/92823.
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Diener, Jacobus Petrus Willem. "Ferromagnetic phase transitions in neutron stars." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71982.
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Thesis (PhD)--Stellenbosch University, 2012.ENGLISH ABSTRACT: We consider the ferromagnetic phase in pure neutron matter as well as charge neutral, betaequilibrated nuclear matter. We employ Quantum Hadrodynamics, a relativistic field theory description of nuclear matter with meson degrees of freedom, and include couplings between the baryon (proton and neutron) magnetic dipole moment as well as between their charge and the magnetic field in the Lagrangian density describing such a system. We vary the strength of the baryon magnetic dipole moment till a non-zero value of the magnetic field, for which the total energy density of the magnetised system is at a minimum, is found. The system is then assumed to be in the ferromagnetic state. The ferromagnetic equation of state is employed to study matter in the neutron star interior. We find that as the density increases the ferromagnetic field does not increase continuously, but exhibit sudden rapid increases. These sudden increases in the magnetic field correspond to shifts between different configurations of the charged particle’s Landau levels and can have significant observational consequences for neutron stars. We also found that although the ferromagnetic phase softens the neutron star equation of state it does not significantly alter the star’s massradius relationship. The properties of magnetised symmetric nuclear matter were also studied. We confirm that magnetised matter tends to be more proton-rich but become more weakly bound for stronger magnetic fields. We show that the behaviour of the compressibility of nuclear matter is influenced by the Landau quantisation and tends to have an oscillatory character as it increases with the magnetic field. The symmetry energy also exhibits similar behaviour.
AFRIKAANSE OPSOMMING: In hierdie studie het ons die ferromagnetiese fase in suiwer neutronmaterie, sowel as in ladingsneutrale, beta-ge¨ekwilibreerde neutronstermaterie, ondersoek. Vir die doeleindes het ons die Kwantum Hadrodinamika-model van kernmaterie gebruik. Dit is ’n relatiwistiese, veldteoretiese model wat mesone inspan om die interaksies tussen die protone en neutrone te bemiddel. Om die impak van die magneetveld te bestudeer, sluit ons ’n koppeling tussen die barioonlading en die magneetveld, asook barioondipoolmoment en die magneetveld, in by die Lagrange digtheid wat ons sisteem beskryf. Om die ferromagnetiese fase te ondersoek, varieer ons die sterkte van die barioondipoolmoment om ’n nie-nul waarde van die magneetveld wat energie digtheid sal minimeer te vind. Die ferromagnetiese toestandsvergelyking word toegepas op materie aan die binnekant van die neutronster en die impak hiervan op die waarneembare eienskappe van die ster word ondersoek. Ons vind dat die ferromagnetiese magneetveld nie kontinu toeneem soos die digtheid verhoog nie. Die skielike toenames in die magneetveld is die gevolg van die sisteem wat die konfigurasie van die gelaaide deeltjies se Landau-vlakke skielik verander en dit kan beduidende waarneembare gevolge vir die ster inhou. Ons vind ook dat die ferromagnetiese fase die toestandsvergelyking versag, maar dat die versagting die massa-radius verhouding van die ster nie grootliks beïnvloed nie. Die eienskappe van gemagnetiseerde kernmaterie word ook ondersoek. Ons bevestig dat gemagnetiseerde materie meer proton-ryk, maar minder sterk gebind word. Ons wys dat die saampersbaarheid van kernmaterie deur die teenwoordigheid van Landau-vlakke beïnvloed word en ossilerend saam met die magneetveld toeneem. Die simmetrie-energie manifesteer ook soortgelyke gedrag.
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Hogg, Michael. "Neutron stars and their terrestrial analogues." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/366019/.
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When we consider in detail the behaviour of a fluid consisting of two (or possibly more) interpenetrating components, the likelihood of dynamical instabilities induced by coupling between the two fluids cannot be ignored. The phenomenon is generic to all such multi fluid systems and as such is appellated the two-stream instability. Mathematically this class of instability is somewhat akin to the more well known Kelvin Helmholtz instability, but is distinguished by the fluids flowing through each other rather than having a clearly defined interface between them. In this thesis we describe in some detail the mechanisms underlying this instability in a simple linear ow scrutinising in particular the growing (unstable) solutions for small harmonic perturbations. We further consider the application of this genre of instabilities to other physical systems, most conspicuously to that of a rotating super fluid body with rotational lag between the components. This case is of particular interest in neutron star physics, where it offers possibilities for exploring behaviour within the core. There also seems to be the chance of exploring this example in laboratory systems. We also take a tentative first step to extending the application and understanding of the two-stream instability by flirting with the analogous observations in a laboratory realisable binary Bose-Einstein Condensate. This laboratory realisation is a first step towards being able to explore physically issues relating to neutron star dynamics. We further discuss general analogue systems for modelling key features of neutron stars in terrestrial laboratories. The possible applications, along with some of the diffculties in using these analogues, are explored.
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Vasisht, Gautam Kulkarni S. R. "Many faces of young neutron stars /." Diss., Pasadena, Calif. : California Institute of Technology, 1996. http://resolver.caltech.edu/CaltechETD:etd-09172008-100913.
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Gullón, Juanes Miguel. "Population Synthesis of isolated Neutron Stars." Doctoral thesis, Universidad de Alicante, 2015. http://hdl.handle.net/10045/53162.
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Neutron Stars present a wide variety from the observational point of view. The advent of new and powerful detectors and instruments has opened a new era where the classical picture of neutrons stars seen as radio-pulsars has been modified with new classes such as magnetars, X-ray Isolated Neutron Stars (XINSs) or Central Compact Objects (CCOs) in Supernova Remnants . In addition to the more than 2500 sources detected in the radio band, more than two hundred have also been detected as X-ray and gamma-ray sources. This number is expected to increase in the near future. Despite this apparent diversity, some studies demand a theory able to explain the different classes in terms of the same physical scenario (Kaspi, 2010), in which the evolution of the magnetic field appears to play an important role (Viganò et al., 2013). The Population Synthesis of Neutron Stars, which is the central subject of this thesis, is an interesting approach to understand the problem, as both intrinsic properties and observational biases are taken into account. These technique is based on Monte Carlo methods, applied to simulate the whole population of neutron stars. The main objective of the thesis has been to perform a multi-wavelength study of the different populations of Neutron Stars focusing in the effects of magneto-thermal evolution. This report consists of a global summary of the objectives, methods and main results of the thesis. It is structured as follows. The first chapter gives an introduction to Neutron Stars. Chapter two is a description of the method of Population Synthesis of Neutron Stars. In chapter three a global discussion of the main results is presented. Chapter four closes the report with the conclusions. An appendix is also included which constitutes a description of a method based on the pulsar current analysis.
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Kaplan, David Lior Ariel Sargent W. L. W. "The diversity of neutron stars: nearby thermally emitting neutron stars and the compact central objects in supernova remnants /." Diss., Pasadena, Calif. : California Institute of Technology, 2004. http://resolver.caltech.edu/CaltechETD:etd-05272004-150045.
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Moreno, Guzmán Fermín. "Accretion onto Neutron Stars: Hydrodynamics and Nucleosynthesis." Doctoral thesis, Universitat Politècnica de Catalunya, 2009. http://hdl.handle.net/10803/6594.
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In the middle of the 70s, some authors suggested that accretion of hydrogen and helium rich material by a neutron star in a binary system, where the companion star would have low mass, could explain thermonuclear bursts observed by the first satellites launched to the space in order to analyze the Xray band of the electromagnetic spectrum. This phenomenon, known as type I X-ray bursts (XRB), is a thermonuclear runaway produced by the themonuclear fusion of the accreted material in degenerated conditions. This kind of explosion from stellar source is the most frequent in our galaxy (and the third, after supernovae and classical novae, in terms of total output energy), because his short recurrence period. Due to the extreme gravitational field of a neutron star it is known that produced nucleosynthesis is not ejected to the interstellar medium but forming part of the neutron star crust.In this work we have tried, first, to study the effects of nuclear uncertainties, related to nuclear reaction rates, in the nucleosynthesis produced during a X-ray burst, and second, to simulate physical properties and associated nucleosynthesis to this kind of events, through hydrodynamical models.
In order to analyze the impact of uncertainties of the nuclear reaction rates in the nucleosynthesis, and due to the prohibitive calculation time with an hydrodinamical code, we have used a post-processing code which we have coupled, for a given set of 10 temperatures and densities profiles, an extensive nuclear reactions network formed by 606 isotopes and 3551 nuclear reactions, whose reaction rates have been modified using to alternative methods. In the first one, every rate has been individually modified, multiplying it by 0.1 and 10, calculating the final nucleosynthesis. This way, it is possible to evaluate the impact in final nucleosynthesis individual variations in the nuclear reaction rates. Also we have analyzed the effects in final nucleosynthesis by modifying the energy associated to each reaction (Q-value). In the second method, nuclear reaction rates have been modified simultaneously, multiplying each one by a random factor which follow a log-normal distribution with a probability of 95.5% of being in the interval [0.1,10]. In order to analyzed this method from an statistically point of view, the nucelosynthesis has been calculated up to 10,000 times, with a Monte Carlo code specifically built to this Thesis, for different set of random numbers. Obtained results with both methods are coincidents and show that for a network formed by 3,500 reactions approximately, only about 60 reactions have an impact in final yields greater than a factor of 2.Finally, we have used an hydrodynamical code, one-dimensional (spherically symmetric), Lagrangian and multi-shell, to which we have coupled a nuclear reactions network formed by 324 isotopes and 1392 reactions with the aim of reproduce physical parameters and nucleosynthesis produced during X-ray bursts. To do that, we have applied this code to different models, analyzing the effect of spatial resolution in the accreted shell, the metallicity of the transferred material as well as the mass of the neutron star, in the final result. For each model, we have simulated different bursts, with energies, luminosities and recurrence times coincidents with observations and, together with the nucleosynthesis, similar to the results obtained by other authors.
A mediados de los años 70, varios autores sugirieron que la acreción de material rico en hidrógeno y helio por parte de una estrella de neutrones, integrante de un sistema binario donde la masa de la estrella compañera fuese pequeña, podría explicar las erupciones termonucleares observadas por los primeros satélites lanzados al espacio para analizar la banda X del espectro electromagnético. Dicho fenómeno, conocido como erupciones de rayos X de tipo I (en inglés, type I X-ray bursts, XRB), consiste en el alud termonuclear producido por la fusión termonuclear del material acretado, en condiciones degeneradas. Este tipo de explosión termonuclear de origen estelar es el más frecuente en nuestra galaxia (y el tercero, tras las supernovas y las novas clásicas, en términos de energía total liberada), debido a su corto periodo de recurrencia. Como consecuencia del extremo campo gravitatorio de una estrella de neutrones, se cree que la nucleosíntesis producida durante este tipo de eventos no es expulsada al medio interestelar, pasando a formar parte de la corteza de la estrella.
En este trabajo hemos intentado, por un lado, estudiar los efectos de las incertidumbres de origen nuclear, asociadas a los ritmos de las reacciones nucleares, en la nucleosíntesis producida durante un X-ray burst; y por otro lado, simular las propiedades físicas y la nucleosíntesis asociada a este tipo de eventos, mediante modelos hidrodinámicos.
Para estudiar el impacto de las incertidumbres de los ritmos de las reacciones nucleares en la nucleosíntesis, y debido a que el tiempo de cálculo con un código hidrodinámico resultaría prohibitivo, hemos utilizado un código de post-procesado al que se ha acoplado, para un conjunto determinado de 10 perfiles de temperatura y densidad, una extensa red de reacciones nucleares, formada por 606 isótopos y 3551 reacciones nucleares, cuyos ritmos de reacción han sido modificados utilizando dos métodos alternativos. En el primero, cada ritmo ha sido modificado individualmente, multiplicándolo por 0.1 y 10, calculándose la nucleosíntesis final. De esta manera, puede evaluarse el impacto que tienen en las abundancias finales las variaciones individuales de los ritmos de las reacciones nucleares.
Así mismo, también se ha analizado el efecto que produce en las abundancias finales el hecho de modificar la energía asociada a cada reacción (Q-value). En el segundo método, los ritmos nucleares se han modificado simultáneamente, multiplicando cada uno de ellos por un factor aleatorio según una distribución log-normal, y cuya probabilidad de encontrarse en el intervalo [0.1,10] es del 95,5%. Para poder hacer una estimación estadística de este último método, se ha calculado la nucleosíntesis hasta 10.000 veces, con un código Monte Carlo específicamente construido para esta Tesis, para diferentes conjuntos de números aleatorios. Los resultados obtenidos con ambos métodos son coincidentes y demuestran que, para una red formada por unas 3500 reacciones nucleares, sólo unas 60 reacciones tienen un impacto en las abundancias finales mayor que un factor 2.
Por último, hemos utilizado un código hidrodinámico, unidimensional (en simetría esférica), Lagrangiano y multicapa, al que se ha acoplado una red de reacciones nucleares formada por 324 isótopos y 1392 reacciones nucleares, con el objetivo de reproducir los parámetros físicos y la nucleosíntesis producida en los X-ray bursts. Para ello, hemos aplicado este código a diferentes modelos, analizando el efecto de la resolución espacial de la capa acretada, la metalicidad del material transferido, así como la masa de la estrella de neutrones, en el resultado final. Para cada modelo, hemos simulado diferentes erupciones, con energías, luminosidades, y periodos de recurrencia, coincidentes con las observaciones y, junto con la nucleosíntesis, similares a los resultados obtenidos por otros autores.
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Beisenkhanova, Neilya. "Cooling of neutron stars with quark core." Thesis, Montana State University, 2012. http://etd.lib.montana.edu/etd/2012/beisenkhanova/BeisenkhanovaN0512.pdf.
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Ordinary neutron stars can undergo two possible scenarios of cooling: with conventional 'standard' neutrino emission processes or with faster 'non-standard' processes. For both of these scenarios various mechanisms have been proposed. As possible nonstandard options, previous detailed studies already explored direct URCA processes involving hyperon-mixed matter and pion condensates. In the current research we explore another possible non-standard scenario - quark cooling where a hybrid star with a quark core undergoes direct URCA cooling. We used the exact evolutionary code originally constructed by Nomoto and Tsuruta (1987) which was modified for quark cooling. We chose a model with a medium equation of state TNI 6, where transition from neutron to quark matter takes place at a critical density of four times the nuclear density. Our results show that low mass stars undergo standard cooling while heavier stars, with mass larger than about 1.45 mass compared to the sun, possess a central core where nonstandard accelerating quark cooling is in operation but it can be suppressed significantly due to density-dependent superfluid property. We showed that our quark cooling scenario can be consistent with the observational data on neutron star temperatures. An important result is that we obtained more realistic cooling behavior than obtained earlier, by adopting a density-dependent superfluid energy gap model, instead of constant gaps employed earlier.
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Price, Steven Curtis. "Rotational and thermal dynamics of neutron stars." Diss., Montana State University, 2012. http://etd.lib.montana.edu/etd/2012/price/PriceS0512.pdf.
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This thesis explores the rotational and thermal dynamics of neutron stars. All neutron stars exhibit irregularities in their spin rates, which may be evidence of coupling between the solid crust and liquid components in the interior. We study short-time scale correlations in the stochastic variations in spin rate, timing noise, in 32 pulsars. Upon subtraction of low frequency wander, we find that in two stars a fluctuation in rotational phase at a given time is correlated with past fluctuations over a correlation time of ~ 10-40 d; over longer times, the fluctuations are uncorrelated. We interpret this result as the signature of a damped rotational mode in the star, excited by the noise process, and likely due to friction between the crust and interior liquid. In the second part of this thesis, we investigate the thermal and magnetic evolution of highly magnetized neutron stars, magnetars. We explore a thermo-resistive instability in the outer crusts of magnetars wherein a perturbation in temperature increases ohmic heating. We show that magnetars of characteristic age T age ~ 10 â��´ yr are unstable over timescales as short as days if strong current sheets are present in the outer crust. This instability could play an important role in the thermal and magnetic field evolution of highly magnetized neutron stars, and may be related to bursting activity in magnetars.
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Gonzalez, Marjorie. "X-ray observations of young neutron stars." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18813.
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The extreme physical properties of neutron stars make them efficient emitters at all wavelengths of the electromagnetic spectrum and, traditionally, they have been extensively studied at radio wavelengths. The neutron stars with the highest estimated magnetic fields (so-called "magnetars") have remarkably different characteristics from the rest of the population: they emit no persistent radio emission but show large amounts of high-energy radiation that is thought to be powered by their large magnetic fields. For this thesis we have studied the X-ray emission properties of various types of young neutron stars, discovering unusual characteristics, constraining long-term behaviour and finding associated nebulae. We have observed the neutron stars PSR B0154+61 and PSR J1119-6127, which have high magnetic fields but otherwise emit normal radio emission. For the latter, unusual thermal X-ray emission was discovered that points to the possible effects of a magnetic field on the surface. Also, this source now represents the youngest neutron star from which thermal emission from the surface has been detected. However, we find no evidence for clear magnetar-like characteristics in these sources. The reason for this discrepancy, as yet unclear and a matter of debate, poses a great challenge to our understanding of the evolution of neutron stars and their emission mechanisms. We have also studied the long-term properties of the "anomalous X-ray pulsar" 4U 0142+61, thought to be a magnetar. We find that changes are present in almost all of its emission characteristics over the last 7 years. The observed changes agree with the general predictions made by the magnetar model of such sources. However, the details of these changes suggest that further work is still needed on the expected emission from these objects. In addition, neutron stars are seen to power extended structures, called pulsar wind nebulae (PWNe), which can radiate large amounts of high-energy emission. HeLes propriétés extrêmes des étoiles à neutrons font de ces objets compacts des émetteurs efficaces dans toutes les longueurs d'ondes du spectre électromagnétique. Cependant, elles ont historiquement été étudiées principalement dans les ondes radios. Les étoiles à neutrons ayant un fort champ magnétique (appelées "magnétars") ont des caractéristiques remarquablement différentes du reste de la population: elles n'émettent pas d'ondes radios mais elles présentent de grandes quantités de radiations à haute énergie causées par le champ magnétique. Pour ce projet, nous avons étudié les propriétés des rayons X provenant de différents types de jeunes étoiles à neutrons, découvert des caractéristiques inattendues, contraint le comportement à long terme et enfin trouvé des nébuleuses associés aux étoiles à neutrons. Tout d'abord, nous avons observé les étoiles à neutrons PSR B0154+61 et PSR J1119-6127. Ces deux objets ont un fort champ magnétique mais ils émettent cependant des ondes radios normales. Pour la seconde, des émissions de rayons X thermiques ont également été découvertes, ce qui suggère les possibles effets du champ magnétique sur la surface. Aussi, cette source est maintenant la plus jeune étoile à neutrons émettant une radiation thermique depuis sa surface. Il n'y a cependant aucune preuve permettant d'associer ces sources aux caractéristiques des magnétars. La raison de cette différence, toujours incomprise et sujette à de nombreux débats, pose un énorme défi à notre compréhension de l'évolution des étoiles à neutrons et de leurs mécanismes d'émission. Ensuite, nous avons également étudié les propriétés à long terme du "pulsar anormal à Rayons X" 4U 0142+61, que l'on pense être un magnétar. Nous trouvons des changements de presque toutes ces caractéristiques d'émission sur les 7 dernières années. Les variations observées sont en accord avec les prédictions suggérées par$
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Hui, Chung-yue, and 許宗宇. "Anisotropic heat transfer inside rotating neutron stars." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B29275611.
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Haskell, Brynmor Dylan Luigi. "Gravitational waves from deformed rotating neutron stars." Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438658.
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Marques, Miguel. "Relativistic rapidly differentially rotating hot neutron stars." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEO007/document.
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Les étoiles à neutrons sont parmi les objets les plus extrêmes dans l'univers. Elles sont des étoiles compactes, nées à la suite d'une explosion de supernova gravitationnelle, au point final de l'évolution stellaire. Le champ gravitationnel y est très fort, et la matière à l'intérieur atteint des densités extrêmement élevées. Elles sont donc des "laboratoires" prometteurs, non seulement pour tester le régime de champ fort en relativité générale, mais aussi pour en apprendre davantage sur la physique nucléaire à haute densité, qui actuellement ne peut pas être reproduit avec des expériences terrestres. Ainsi, les étoiles à neutrons nous permettent d'adresser des questions telles que l'existence éventuelle de particules autres que nucléons à haute-densité. À cause de la naissance violente de ces objets, les étoiles à neutrons très jeunes, que l'on appelle proto-étoiles à neutrons, sont également très chaudes, et souvent en rotation différentielle rapide. Dans cette thèse nous avons pour but de développer un modèle stationnaire d'une telle proto-étoile à neutrons.Ainsi, nous présentons une nouvelle méthode pour calculer numériquement les équations d'équilibre d'un fluide parfait relativiste, axisymétrique et stationnaire, en rotation différentielle et à température finie, valable pour une équation d'état réaliste. Nous présentons en détail le code (accessible au public) développé. Nous avons appliqué ce code avec des nouvelles équations d'état réalistes à température finie, basée sur une théorie relativiste du champ moyen, en incluant tous les degrés de liberté hyperoniques. Nous avons calculé des modèles relativistes stationnaires de proto-étoiles à neutrons en rotation différentielle rapide. Nous allons discuter les applications de nos modèles pour explorer plus en détail la physique de ces objetsNeutron stars are among the most extreme objects in the universe. They are compact stars born as the aftermath of a core-collapse supernova explosion, at the endpoint of stellar evolution, with a strong gravitational field, and extremely high densities. They are therefore promising 'laboratories', not only to test the strong-field regime of general relativity, but also to learn about nuclear physics in the high density regime, which presently is not accessible in earth based experiments. This allows to address questions such as the possible existence of particles other than nucleons at high-densities. As a consequence of the violent birth of these objects, new-born (proto-)neutron stars are extremely hot and, in general, rapidly rotating, which raises interesting problems in the task of developing a stationary model of such objects.In this thesis, we present a new self-consistent method to numerically compute the equilibrium equations of stationary axisymmetric relativistic (differentially) rotating perfect fluids at finite temperature, with a realistic equation of state. We introduce in detail the (publicly available) code in which we implemented the described numerical scheme. We use newly developed realistic equations of state with finite temperature, which are based on density dependent relativistic mean field theory, and in which all hyperonic degrees of freedom are included, to compute realistic stationary relativistic models of rapidly differentially rotating proto-neutron stars. We discuss future applications of our code for further exploring the physics of proto-neutron stars
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Watts, Anna Louise. "The dynamics of differentially rotating neutron stars." Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/50593/.
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This thesis investigates the effect of rapid accretion and differential rotation on neutron star oscillations. The research is motivated by the fact that vibrating neutron stars are a promising source of gravitational waves. The first part of the thesis is a study of a nascent neutron star accreting supernova remnant material. We model an unstable r-mode oscillation that leads to the emission of gravitational waves, and the torques and heating associated with rapid accretion onto a star with a magnetic field. We consider the consequences for both gravitational wave emission and the rotation rate of the star. The main part of the thesis addresses differential rotation. This is likely to arise at times, such as the immediate aftermath of the supernova, when we expect strong vibrations. We focus on two factors unique to differentially rotating systems; dynamical shear instabilities, and the existence of a corotation band (a frequency band in which mode pattern speed matches the local angular velocity). Using a simple model, we find dynamical shear instabilities that arise where modes cross into the corotation band, if the degree of differential rotation exceeds a certain threshold. Recently, several authors have reported the discovery of dynamical instabilities in differentially rotating stars at low values of the ratio of kinetic to potential energy. We demonstrate that our instability mechanism explains all of the reported features of these instabilities. We also investigate the nature of oscillations within the corotation band. The band gives rise to a continuous spectrum whose collective physical perturbation exhibits complicated temporal behaviour. We also report the existence of modes within the continuous spectrum that appear physically indistinguishable from the discrete modes outside the band, despite the singular nature of their eigenfunctions.
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Krüger, Christian. "Seismology of adolescent general relativistic neutron stars." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/384187/.
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Lander, Samuel Kenneth. "Equilibria and oscillations of magnetised neutron stars." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/167473/.
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We investigate equilibrium configurations and oscillation spectra of neutron stars, modelled as rotating magnetised fluid bodies in Newtonian gravity. We also explore the idea that these model neutron stars could have dynamics analogous to rigid-body free precession. In axisymmetry, the equations of magnetohydrodynamics reduce to a purely toroidal-field case and a mixed-field case (with a purely poloidal-field limit). We solve these equations using a nonlinear code which finds stationary rotating magnetised stars by an iterative procedure. We find that despite the general nature of our approach, the mixed-field configurations we produce are all dominated by their poloidal component. We calculate distortions induced both by magnetic fields and by rotation; our results suggest that the relationship between the magnetic energy and the induced ellipticity should be close to linear for all known neutron stars. We then investigate the oscillation spectra of neutron stars, using these stationary configurations as a background on which to study perturbations. This is done by evolving the perturbations numerically, making the Cowling approximation and specialising to purely toroidal fields for simplicity. The results of the evolutions show a number of magnetically-restored Alfv´en modes. We find that in a rotating star pure inertial and pure Alfv´en modes are replaced by hybrid magneto-inertial modes. We also show that magnetic fields appear to reduce the effect of the r-mode instability. Finally, we look at precession-like dynamics in magnetised fluid stars, using both analytic and numerical methods. Whilst these studies are only preliminary, they indicate deficiencies in previous research on this topic. We suggest ways in which the problem of magnetised-fluid precession could be better understood.
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Taverna, Roberto. "Polarized emission from highly-magnetized neutron stars." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424483.
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The study of magnetars, the anomalous X-ray pulsars (AXPs) and the soft gamma repeaters (SGRs), and of X-ray Dim Isolated Neutron Stars (XDINSs) is of particular relevance, since these objects exhibit the strongest magnetic fields ever observed in the universe (10^13-10^15 G) and represent the only laboratories where physics in the presence of such strong magnetic fields can be tested. Until now, these peculiar neutron stars have been investigated through spectroscopic and timing measurements, which led to validate the theoretical models developed to explain their phenomenology, as in the case of the "twisted magnetosphere'' model for magnetars or the different surface emission models for XDINSs. Nevertheless, this kind of analysis alone is far from providing complete information. In this respect, X-ray polarimetry may disclose an entirely new approach in the study of highly magnetized neutron stars. Radiation emitted in the presence of strong magnetic fields, in fact, is expected to be highly polarized; polarization measurements provide two additional observables, the linear polarization fraction and the polarization angle, that can unambiguously determine the model parameters also when spectral analysis alone fails. The polarization signal that an observer at infinity would collect, however, do not necessary coincide with model predictions for the polarization at the surface, due to the effects of quantum electrodynamics in the highly magnetized vacuum around the star, coupled with the rotation of the Stokes parameters in the plane perpendicular to the line of sight, induced by the non-uniform magnetic field. In this thesis I present the results of the numerical codes I developed to simulate the polarization pattern, both at the surface and as observed at infinity, of the radiation emitted from highly magnetized, isolated neutron stars, using as templates the bright AXP 1RXS J170849.0-400910 and the XDINS RX J1856.5-3754. I demonstrate that polarization measurements can indeed provide key information about the physical and geometrical properties of these sources, allowing to directly test theoretical models. This work is also relevant in view of the launch of new-generation X-ray polarimeters, currently under development, like the X-ray Imaging Polarimeter Explorer (XIPE). For this reason, I also compare theoretical models with XIPE simulated observations, in order to show how polarization measurements can be used to extract the values of magnetospheric parameters and viewing angles.Lo studio delle magnetars, anomalous X-ray pulsars (AXPs) e soft gamma repeaters (SGRs), e delle X-ray Dim Isolated Neutron Stars (XDINSs) è di particolare rilevanza, dal momento che questi oggetti mostrano i più forti campi magnetici mai osservati nell'universo (10^13-10^15 G) e rappresentano i soli laboratori dove la fisica in presenza di campi magnetici così forti può essere testata. Fino ad ora, queste particolari stelle di neutroni sono state studiate attraverso misure spettroscopiche e di timing, che hanno portato a corroborare i modelli teorici formulati per spiegare la loro fenomenologia, come nel caso del "twisted magnetosphere'' model per le magnetars o dei diversi modelli di emissione superficiale per le XDINSs. Cionondimeno, questa analisi da sola non riesce a fornire informazioni complete. A questo riguardo, la polarimetria X può svelare un approccio completamente nuovo nello studio delle stelle di neutroni altamente magnetizzate. La radiazione emessa in presenza di forti campi magnetici, infatti, è attesa essere altamente polarizzata; le misure di polarizzazione forniscono due osservabili aggiuntivi, la frazione di polarizzazione lineare e l'angolo di polarizzazione, che possono determinare senza ambiguità i parametri dei modelli anche quando la sola analisi spettrale si dimostra insufficiente. Il segnale di polarizzazione che un osservatore riceve all'infinito, tuttavia, non coincide necessariamente con ciò che i modelli predicono per la polarizzazione alla superficie, a causa degli effetti dell'elettrodinamica quantistica nel vuoto fortemente magnetizzato attorno alla stella, accoppiato con la rotazione dei parametri di Stokes nel piano perpendicolare alla linea di vista, indotta dal campo magnetico non uniforme. In questa tesi presento i risultati dei codici numerici che ho sviluppato per simulare il pattern di polarizzazione, sia alla superficie che all'infinito, della radiazione emessa da stelle di neutroni isolate altamente magnetizzate, usando come modelli la luminosa AXP 1RXS 170849.0-400910 e la XDINS RX J1856.5-3754. Dimostrerò che le misure di polarizzazione possono effettivamente fornire informazioni cruciali sulle proprietà fisiche e geometriche di queste sorgenti, permettendo di testare direttamente i modelli teorici. Questo lavoro è inoltre rilevante in vista del lancio di polarimetri X di nuova generazione, attualmente in fase di sviluppo, come l'X-ray Imaging Polarimetry Explorer (XIPE). Per questa ragione, confronterò i modelli teorici con osservazioni simulate di XIPE, allo scopo di mostrare come le misure di polarizzazione possono essere utilizzate per estrarre i valori dei parametri relativi alla magnetosfera e gli angoli di vista.
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Pfahl, Eric D. (Eric David) 1976. "The galactic population of binaries containing neutron stars." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8487.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 2002.Includes bibliographical references (p. 127-140).
The research presented herein is a theoretical investigation of the formation, evolution, and ultimate fate of low-, intermediate-, and high-mass X-ray binaries (L/I/HMXBs). The primary theoretical tool used throughout is binary population synthesis. Results of these calculations are used to account for the numbers and properties of observed X-ray binaries and their descendants, as well as to direct future observational and theoretical work. Combining binary population synthesis and binary stellar evolution calculations, I present a systematic population study of L/IMXBs in the Galactic plane. Since full stellar evolution calculations are used to model the X-ray binary phase, it is possible to make detailed comparisons between the theoretical models and observations. It is demonstrated quantitatively that IMXBs probably play a crucial role in shaping the population of LMXBs observed at the current epoch, as well as their descendant binary millisecond radio pulsars. Recently, a new class of HMXBs has emerged, distinguished from other HMXBs by their wide, nearly circular orbits. I show that the discovery of a significant number of such systems is at odds with the conventional wisdom that most neutron stars receive very large "kick" speeds at birth. This problem may be rectified in a self-consistent way if the kick speed depends on the rotation rate of the pre-collapse core, which I propose is strongly influenced by the evolution of the neutron-star progenitor in a binary system. The reasonable suggestion that certain globular clusters contain nearly 1000 neutron stars conflicts with the large mean kick speeds estimated from observations of isolated radio pulsars, which are 5 to 10 times the present cluster escape speeds.
(cont.) Therefore, most neutron stars born from single progenitors should have been ejected from their host clusters. I show that many more neutron stars are retained if a significant fraction are formed with massive stellar companions, but that the retained fraction is still too small to account for the inferred large numbers of neutron stars at the current epoch. Several alternative hypotheses are discussed, including the intriguing possibility that globular clusters we see today were ten times more massive in the distant past. The Chandra X-ray Observatory has revealed hundreds of previously undetected point sources in a small field about the Galactic center. I show that the majority of these sources may be neutron stars accreting from the winds of unevolved companion stars. Infrared observations are proposed to search for the stellar counterparts of the X-ray sources.
by Eric D. Pfahl.
Ph.D.
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Medin, Zach, Marina von Steinkirch, Alan C. Calder, Christopher J. Fontes, Chris L. Fryer, and Aimee L. Hungerford. "MODEL ATMOSPHERES FOR X-RAY BURSTING NEUTRON STARS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/624031.
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The hydrogen and helium accreted by X-ray bursting neutron stars is periodically consumed in runaway thermonuclear reactions that cause the entire surface to glow brightly in X-rays for a few seconds. With models of the emission, the mass and radius of the neutron star can be inferred from the observations. By simultaneously probing neutron star masses and radii, X-ray bursts (XRBs) are one of the strongest diagnostics of the nature of matter at extremely high densities. Accurate determinations of these parameters are difficult, however, due to the highly non-ideal nature of the atmospheres where XRBs occur. Observations from X-ray telescopes such as RXTE and NuStar can potentially place strong constraints on nuclear matter once uncertainties in atmosphere models have been reduced. Here we discuss current progress on modeling atmospheres of X-ray bursting neutron stars and some of the challenges still to be overcome.
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Antonelli, M. "MODELLING SUPERFLUID NEUTRON STARS APPLICATIONS TO PULSAR GLITCHES." Doctoral thesis, Università degli Studi di Milano, 2018. http://hdl.handle.net/2434/544419.
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In this dissertation I discuss how observations of the maximum glitch occurred in a
certain pulsar provides a test for the microscopic physics of neutron star interiors, in
particular the pinning forces (a parameter which effectively describes the strength of
the vortex-lattice interaction at the mesoscopic scale). Conversely, by fixing the input
parameters by taking estimates from recent literature, it is possible to estimate the mass of
a glitching pulsar. A proof of concept of this thesis is given by constructing a quantitative
model for pulsar rotational dynamics that can consistently encode state of the art models
of the pinning force between vortices and ions in the crust, as well as the stratified structure
of a neutron star. This point is far from being secondary as most studies on pulsar glitches
are based on body-averaged models or differential models that tacitly assume a cylindrical
symmetry, not consistent with the spherically layered structure.
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Brook, Paul Richard. "The variability of radio pulsars." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:65ae413c-cd12-408b-843c-60886cecf1b7.
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Neutron stars are amongst the most exotic objects known in the universe; more than a solar mass of material is squeezed into an object the size of a city, leading to a density comparable to that of an atomic nucleus. They have a surface magnetic field which is typically around a trillion times stronger than the magnetic field here on Earth, and we have observed them to spin up to around 700 times per second. The existence of neutron stars was first proposed by Baade and Zwicky in 1934 but later graduated from theory to fact in 1967 as the first pulses were detected by Jocelyn Bell-Burnell, a then graduate student at the University of Cambridge. There are now well over 2000 neutron stars whose radio emission beams point at, and have been detected on Earth. We call these objects pulsars. Because of their remarkable properties, pulsars are very useful to physicists, who can employ them as precision timing tools due to the unwavering nature of their emission and of their rotation. Having an array of ultra-accurate clocks scattered throughout our galaxy is very useful for performing astrophysical experiments. In particular, precise pulsar timing measurements and the models that explain them, will permit the direct detection of gravitational radiation; a stochastic background initially, and potentially the individual signals from supermassive black hole binaries. Our models of pulsar behaviour are so precise that we are now able to notice even slight departures from them; we are starting to see that unmodelled variability in pulsars occurs over a broad range of timescales, both in emission and in rotation. Any unmodelled variability is, of course, detrimental to the pulsar's utility as a precision timing tool, and presents a problem when looking for the faint effects of a passing gravitational wave. We are hoping that pulsar timing arrays will detect gravitational radiation in the coming decade, but this depends, in part, on our ability to understand and mitigate the effects of the unmodelled intrinsic instabilities that we are observing. One important clue as to the nature of the variability in pulsar emission and rotation, is the emerging relationship between the two; we sometimes observe correlation on timescales of months and years. We have been observing pulsars for almost fifty years and our expanding datasets now document decades of pulsar behaviour. This gives us the ability to investigate pulsar variability on a range of timescales and to gain an insight into the physical processes that govern these enigmatic objects. In this thesis I describe new techniques to detect and analyse the emission and rotational variability of radio pulsars. We have employed these techniques on a 24 year pulsar dataset to unearth a striking new example of a dramatic and simultaneous shift in a pulsar's emission and rotation. We hypothesise that this event was caused by an asteroid interaction, although other explanations are also possible. Our variability techniques have also been used to analyse data from 168 young, energetic pulsars. In this thesis we present results from the nine most interesting. Of these, we have found some level of correlated variability in seven, one of which displays it very strongly. We have also assessed the emission stability of the NANOGrav millisecond pulsars and have found differing degrees of variability, due to both instrumental and astrophysical causes. Finally, we propose a method of probing the relationship between emission and rotation on short-timescales and, using a simulation, we have shown the conditions under which this is possible. Throughout the work, we address the variability in pulsar emission, rotation and links between the two, with the aim of improving pulsar timing, attaining a consolidated understanding of the diverse variable phenomena observed and elucidating the evolutionary path taken by pulsars.
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周海峰 and Hoi-fung Chau. "Superfluid inside neutron stars and their signature of existence." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1992. http://hub.hku.hk/bib/B31232978.
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The Best PhD Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,1991-1993published_or_final_version
Physics
Doctoral
Doctor of Philosophy
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White, Frances. "Geometrical and physical aspects of rotating neutron stars models." Thesis, University of Portsmouth, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424210.
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Deaton, Michael Brett. "Neutrinos in mergers of neutron stars with black holes." Thesis, Washington State University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3732682.
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Mergers of a neutron star and a black hole are interesting because of the dual complexity of the black hole's strong gravity and the neutron star's nuclear-density fluid. Mergers can yield short-lived nuclear accretion disks, emitting copious neutrinos. This radiation may change the thermodynamic state of the disk itself, may drive an ultrarelativistic jet of electrons and positrons, may oscillate in its flavor content, may irradiate surrounding matter, playing a role in nucleosynthesis, and may be detected directly.
In this thesis I present a model of such a merger, its remnant accretion disk, and its neutrino emission. In particular, we evolve a neutron star—black hole merger through ∼100 ms, solving the full general relativistic hydrodynamics equations, from inspiral through merger and accretion epochs. We treat the neutrinos approximately, using a leakage framework, which accounts for local energy losses and composition drift in the fluid due to escaping neutrinos. We use geodesic ray tracing on a late time slice of the model to calculate the full spatial-, angular-, and energy-dependence of the neutrino distribution function around the accretion disk. This distribution then serves in a computation of the energy available to form a jet via neutrino-antineutrino annihilation in the disk funnel. In this scenario, we find that enough energy is deposited to drive a jet of short-gamma-ray-burst-energy by neutrino processes alone.
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Lemon, Tim. "Simulations of jets from neutron stars and black holes." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/378941/.
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Postnikov, Sergey A. "Topics in the Physics and Astrophysics of Neutron Stars." Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1259174094.
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Kolomeitsev, E. E., Burkhard Kämpfer, and D. N. Voskresensky. "Contribution of the massive photon decay channel to the neutrino cooling of neutron stars." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-31717.
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The role of the massive photon decay via intermediate states of electron-electron-holes and proton-proton-holes into neutrino-anti-neutrino pairs in the course of neutron star cooling is investigated. These reactions may ba operative in hot neutron stars in the region of proton pairing. The corresponding contribution to the neutrino emissivity is calculated. It varies with the temperature as T3/2e−mγ/T for T < m γ, where mγ is an effective photon mass in superconducting matter. Estimates show that this process appears as strong cooling channel of neutron stars at temperatures T ≈ ( 10^9 - 10^10) K.
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Kolomeitsev, E. E., Burkhard Kämpfer, and D. N. Voskresensky. "Contribution of the massive photon decay channel to the neutrino cooling of neutron stars." Forschungszentrum Rossendorf, 1995. https://hzdr.qucosa.de/id/qucosa%3A21997.
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The role of the massive photon decay via intermediate states of electron-electron-holes and proton-proton-holes into neutrino-anti-neutrino pairs in the course of neutron star cooling is investigated. These reactions may ba operative in hot neutron stars in the region of proton pairing. The corresponding contribution to the neutrino emissivity is calculated. It varies with the temperature as T3/2e−mγ/T for T < m γ, where mγ is an effective photon mass in superconducting matter. Estimates show that this process appears as strong cooling channel of neutron stars at temperatures T ≈ ( 10^9 - 10^10) K.
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Flanagan, Claire Susan. "Observations of glitches in PSR 0833-45 and 1641-45." Thesis, Rhodes University, 1996. http://hdl.handle.net/10962/d1005266.
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An eleven-year series of radio timing observations of 0833- 45 (Vela) and PSR 1641- 45 is presented. During this time, five large spin-ups ("glitches") were observed in 0833- 45 and one in 1641-45. The stellar response to these events is investigated, and the three relat ively long complete inter-glitch intervals in 0833-45 are modeled. The results are of relevance to studies of the interiors of neutron stars. The initial aim of the project - to obtain good observational coverage of large glitches in the Vela pulsar - was successfully achieved, and high quality observations of the periods between glitches were obtained as a by-product. The results of the analysis presented here provide support for the existence of both linear and non-linear coupling in the Vela pulsar, and put a limit on the former in PSR 1641- 45. The recently observed existence of a rapidly recovering component of part of a glitch in Vela was verified in the subsequent glitch, although there is now evidence to contradict the suggestion that this component involves a particular region of the star that is implicated in every glitch. Observations of a recent glitch in the same pulsar have resolved a small component of the spin-up; such a component has not been reported for any other large glitch.
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張承民 and Chengmin Zhang. "The evolution of neutron star magnetic fields." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31241359.
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Zhang, Chengmin. "The evolution of neutron star magnetic fields /." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21687559.
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丁群英 and Kwan-ying Winnis Ding. "Magnetic field decay of neutron star: effectsof interpinning of 3P2 neutron superfluid and 1S0 protonsuperconducting fluid." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1992. http://hub.hku.hk/bib/B31210764.
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Raithel, Carolyn A., Feryal Özel, and Dimitrios Psaltis. "FROM NEUTRON STAR OBSERVABLES TO THE EQUATION OF STATE. I. AN OPTIMAL PARAMETRIZATION." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622054.
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The increasing number and precision of measurements of neutron star masses, radii, and, in the near future, moments of inertia offer the possibility of precisely determining the neutron star equation of state (EOS). One way to facilitate the mapping of observables to the EOS is through a parametrization of the latter. We present here a generic method for optimizing the parametrization of any physically allowed EOS. We use mock EOS that incorporate physically diverse and extreme behavior to test how well our parametrization reproduces the global properties of the stars, by minimizing the errors in the observables of mass, radius, and the moment of inertia. We find that using piecewise polytropes and sampling the EOS with five fiducial densities between similar to 1-8 times the nuclear saturation density results in optimal errors for the smallest number of parameters. Specifically, it recreates the radii of the assumed EOS to within less than 0.5 km for the extreme mock EOS and to within less than 0.12 km for 95% of a sample of 42 proposed, physically motivated EOS. Such a parametrization is also able to reproduce the maximum mass to within 0.04 M-circle dot and the moment of inertia of a 1.338 M-circle dot. neutron star to within less than 10% for 95% of the proposed sample of EOS.
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Ding, Kwan-ying Winnis. "Magnetic field decay of neutron star : effects of interpinning of 3P2 neutron superfluid and 1S0 proton superconducting fluid /." [Hong Kong : University of Hong Kong], 1992. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13340396.
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Birkl, Reiner. "Stationary, axisymmetric neutron stars with meridional circulation in general relativity." kostenfrei, 2010. https://mediatum2.ub.tum.de/node?id=966092.
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Carriere, Josef. "Neutron stars and the equation of state of dense matter." [Bloomington, Ind.] : Indiana University, 2005. http://wwwlib.umi.com/dissertations/fullcit/3183485.
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Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2005.Source: Dissertation Abstracts International, Volume: 66-08, Section: B, page: 4269. Adviser: Charles J. Horowitz. Title from dissertation home page (viewed Oct. 10, 2006).
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Oosterbroek, Tim. "Spectral and time variability in black holes and neutron stars." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 1995. http://dare.uva.nl/document/92550.
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Bastarrika, Mikel. "Bayesian analysis of burst gravitational waves from galactic neutron stars." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/2363/.
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This thesis summarises my work in relation to data analysis for gravitational wave detection. Most of the personal contribution relates to the assessment of the detectability of potential burst-type gravitational wave signals from the galactic population of neutron stars and to the parameter estimation of the models used to represent these signals. A small part of the work, confined to the last chapter, describes the experimental work carried at the beginning of the research period and aimed to measure the shot-noise level of the modulated laser-light in the gravitational wave detectors. Chapter 1 is introductory and presents generic information about gravitational wave radiation, a postulate of the theory of general relativity. The polarisation of the radiation and the approximate values of amplitudes and frequencies of the signals expected from astrophysical events are presented, together with most important gravitational radiation sources for ground-based detectors. Chapter 2 presents the study on the detectability of burst-type gravitational wave signals incoming from neutron stars located in our galaxy. Three differently shaped galactic neutron star populations are introduced and the detectability of ground-based detectors to signals of different polarisation degree coming from these source populations is investigated. Based on the time- and polarisation-averaged antenna pattern and antenna power values, approximated by Monte Carlo methods, detectability is measured in terms of a) the geographical location and orientation of hypothetical detectors, and b) the current detectors, either working individually or as a part of a network. Also, the sidereal times at which each detector is more sensitive to the sources of the neutron star populations defined are inferred. Chapter 3 introduces a mathematical model of the burst-type gravitational wave ringdown signal investigated in this work, which represents a short-lived gravitational polarised radiation generated by an oscillating neutron star: an exponentially damped sinusoid comprised of a sine and a cosine component, of the same frequency but different amplitude, as the two polarisation components of the signal. The model of the signal is given, in the time- and in the frequency-domain. Chapter 4 is devoted to present the Bayesian probability tools necessary to carry out ‘model comparison’ and ‘parameter estimation’ for the detectability study of our particular burst-type signal. Comparison of models allows choosing the one that better represents the data and subsequently focusing on in order to compute the most likely parameter values of that model. Also, in this section, the way in which the detector data can be simulated in the frequency domain, combining the signal and a noise realisation corresponding to the power spectrum of the noise that characterizes the detector, is explained. The likelihood function for a signal corresponding to one oscillation mode and seen by one detector is derived both in the time- and in the frequency-domain. The nested sampling technique is summarised, a useful tool to compute effectively the marginal likelihood of the hypotheses considered. Chapter 5 presents the results of the model selection and the parameter estimation exercise. The expression of the likelihood is generalised so that it can adopt more than one oscillation mode and been seen by various detectors of a network. Depending whether one, f-mode, or two oscillation modes, f and p, are suspect, two different scenarios of various hypotheses are considered. For each hypothesis the minimum strength of the signal to claim detection is studied and a parameter estimation exercise is carried out to characterise the signal and define the location of the source in the sky. Signals of known parameters and differing strengths were injected into the synthetic noise of three advanced detectors comprising a network. The values of the parameters were estimated using Bayesian inference for two different scenarios: when only the f-mode is suspect (scenario 1), or when both f- and p-modes are suspect (scenario 2). Posterior probabilities of the parameters in Scenario 1 are better defined and constrained than those for Scenario 2, due to the added uncertainty of including another oscillation mode. As expected, the uncertainty of the probability distributions of the parameter values decreases and the mode shifts toward the exact injected value as the signal strength increases. For both scenarios the frequency value can be accurately estimated, but not so well the damping time, especially for the p-mode oscillation, which is suspected to have longer time durations than f-modes, typically several seconds. The ability to estimate the polarisation degree of the signal is also quite limited and strong signals are required for the mode of the distribution to approximate the exact value. Similarly, determining the most probable location for the source is possible in both scenarios. The two-fold degeneracy of the sky position and related to the travel time of the signal to the detectors has been broken; relatively strong (high SNR) signals, especially for scenario 2, are needed for the source location to be constrained with accuracy. Chapter 6 presents the experimental work carried out, by which the measuring of the shot-noise level of differently modulated and demodulated laser light was intended. Due to the poor outcome of this experiment and the lack of useful results the emphasis has been placed on a detailed description of the modulation apparatus, opto-electronic set up and the control system put together. Chapter 7 looks to the future and briefly presents how to take this data analysis work forward.
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姚昌銓 and Cheong-chuen Yao. "Properties of neutron stars in the relativistic mean field theory." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B30409135.
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