Journal articles on the topic 'TOV Equation'
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1
Bhatti, M. Z., Z. Yousaf, and Zarnoor. "Stability of charged neutron star in Palatini f(R) gravity." Modern Physics Letters A 34, no. 31 (October 7, 2019): 1950252. http://dx.doi.org/10.1142/s0217732319502523.
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In this work, we discuss the stability of charged neutron star in the background of [Formula: see text] gravity and construct the generalized Tolman–Oppenheimer–Volkoff (TOV) equations. For this, we consider static spherically symmetric geometry to construct the hydrostatic equilibrium equation and deduce TOV equations from modified field equations with electromagnetic effects. We conclude that the generalized TOV equation depicts the stable stars configuration independent of the generic function of the modified gravity if the condition of uniform entropy and chemical composition is assumed.
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Alloy, Marcelo D., Débora P. Menezes, and Manuel Malheiro. "Ansatz for Dense Matter Equation of State." International Journal of Modern Physics: Conference Series 45 (January 2017): 1760049. http://dx.doi.org/10.1142/s2010194517600497.
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The aim of the present work is to try to find an equation of state (EoS) directly from the solution of the Tolman-Oppenheimer-Volkoff (TOV) equations subject to known observational constraints to the maximum mass and corresponding radius and baryonic mass. Hence, instead of solving the TOV equations with an EoS that enters as input, we obtain an EoS as output.
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Carvalho, G. A., S. I. Dos Santos, P. H. R. S. Moraes, and M. Malheiro. "Strange stars in energy–momentum-conserved f(R,T) gravity." International Journal of Modern Physics D 29, no. 10 (July 2020): 2050075. http://dx.doi.org/10.1142/s0218271820500753.
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For the accurate understanding of compact astrophysical objects, the Tolmann–Oppenheimer–Volkoff (TOV) equation has proved to be of great use. Nowadays, it has been derived in many alternative gravity theories, yielding the prediction of different macroscopic features for such compact objects. In this work, we apply the TOV equation of the energy–momentum–conserved version of the [Formula: see text] gravity theory to strange quark stars. The [Formula: see text] theory, with [Formula: see text] being a generic function of the Ricci scalar [Formula: see text] and trace of the energy–momentum tensor [Formula: see text] to replace [Formula: see text] in the Einstein–Hilbert gravitational action, has shown to provide a very interesting alternative to the cosmological constant [Formula: see text] in a cosmological scenario, particularly in the energy–momentum conserved case (a general [Formula: see text] function does not conserve the energy–momentum tensor). Here, we impose the condition [Formula: see text] to the astrophysical case, particularly the hydrostatic equilibrium of strange stars. We solve the TOV equation by taking into account linear equations of state to describe matter inside strange stars, such as [Formula: see text] and [Formula: see text], known as the MIT bag model, with [Formula: see text] the pressure and [Formula: see text] the energy density of the star, [Formula: see text] constant and [Formula: see text] the bag constant.
4
Rather, Ishfaq A., Asloob A. Rather, Ilídio Lopes, V. Dexheimer, A. A. Usmani, and S. K. Patra. "Magnetic-field Induced Deformation in Hybrid Stars." Astrophysical Journal 943, no. 1 (January 1, 2023): 52. http://dx.doi.org/10.3847/1538-4357/aca85c.
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Abstract The effects of strong magnetic fields on the deconfinement phase transition expected to take place in the interior of massive neutron stars are studied in detail for the first time. For hadronic matter, the very general density-dependent relativistic mean field model is employed, while the simple, but effective vector-enhanced bag model is used to study quark matter. Magnetic-field effects are incorporated into the matter equation of state and in the general-relativity solutions, which also satisfy Maxwell’s equations. We find that for large values of magnetic dipole moment, the maximum mass, canonical mass radius, and dimensionless tidal deformability obtained for stars using spherically symmetric Tolman–Oppenheimer–Volkoff (TOV) equations and axisymmetric solutions attained through the LORENE library differ considerably. The deviations depend on the stiffness of the equation of state and on the star mass being analyzed. This points to the fact that, unlike what was assumed previously in the literature, magnetic field thresholds for the approximation of isotropic stars and the acceptable use of TOV equations depend on the matter composition and interactions.
5
Riazi, Nematollah, S. Sedigheh Hashemi, S. Naseh Sajadi, and Shahrokh Assyyaee. "A new class of anisotropic solutions of the generalized TOV equation." Canadian Journal of Physics 94, no. 10 (October 2016): 1093–101. http://dx.doi.org/10.1139/cjp-2016-0365.
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We present gravitating relativistic spheres composed of an anisotropic, barotropic fluid. We assume a bi-polytropic equation of state that has both linear and power-law terms. The generalized Tolman–Oppenheimer–Volkoff (TOV) equation, which describes the hydrostatic equilibrium, is used and the full system of equations is solved for solutions that are regular at the origin and asymptotically flat. Conditions for the appearance of horizon and a basic treatment of stability are also presented.
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Albino, M. B., F. S. Navarra, R. Fariello, and G. Lugones. "The nature of the quark-hadron phase transition in hybrid stars and the mass-radius diagram." Journal of Physics: Conference Series 2340, no. 1 (September 1, 2022): 012015. http://dx.doi.org/10.1088/1742-6596/2340/1/012015.
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Abstract In this work, we use a hybrid equation of state that allows us to choose the smoothness of the quark-hadron phase transition, by choosing the value of a continuous parameter μc . To describe the hadron phase, we use an equation of state (EoS) based on a chiral effective field theory (cEFT), and for the quark phase we use the equation of state of the MFTQCD (Mean Field Theory of QCD). We solve simultaneously the TOV equations and the tidal deformability equations and contruct the mass-radius and deformability-mass diagrams for several values of the parameter μc . We find that the curves in these two diagrams are almost insensitive to the smoothness of the phase transition.
7
Abbas, G., and M. R. Shahzad. "Quintessence compact stars with Vaidya–Tikekar type grr for anisotropic fluid." Canadian Journal of Physics 98, no. 9 (September 2020): 869–76. http://dx.doi.org/10.1139/cjp-2019-0596.
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The present study provides a new solution to the Einstein field equations for anisotropic matter configuration in static and spherically symmetric space–time. By taking benefit from the conformal Killing vector (CKV) technique and quintessence field specified by a parameter ωq as –1 < ωq < –1/3, we generate an exact solution to the field equations. For this investigation, we have used a specific form of metric potential taken fromVaidya–Tikekar (J. Astrophys. Astron. 3, 325 (1982)) geometry. To canvass the physical plausibility of the presented solution, we explored some analytical expressions such as energy conditions, the TOV equation, stability analysis, and equation of state parameters. We present graphical analysis of the necessary analytical expressions that revealed that our solution satisfies the necessary physical conditions.
8
Zhang, Z., X. Wang, H. Zhang, and J. Shi. "Entropy of nonsingular self-gravitating polytropes and their TOV equation." Il Nuovo Cimento B 106, no. 11 (November 1991): 1189–94. http://dx.doi.org/10.1007/bf02728656.
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MIRZA, BABUR M. "THE EQUILIBRIUM STRUCTURE OF CHARGED ROTATING RELATIVISTIC STARS." International Journal of Modern Physics D 17, no. 12 (November 2008): 2291–304. http://dx.doi.org/10.1142/s021827180801387x.
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General relativistic equilibrium conditions imply that an electrically charged compact star, in a spherically symmetric configuration, can sustain a huge amount of electric charge (up to 1020 C). The equilibrium, however, is reached under very critical conditions such that a perturbation to the stellar structure can cause these systems to collapse. We study the effects of rotation in charged compact stars and obtain conditions, the modified Tolman–Oppenheimer–Volkoff (TOV) equations, under which such stars form a stable gravitational system against Coulomb repulsion. We assume the star to be rotating slowly. We also assume that the charge density is proportional to the mass density everywhere inside the star. The modified TOV equations for hydrostatic equilibrium are integrated numerically for the general equation of state for a polytrope. The detailed numerical study shows that the centrifugal force adds to the Coulomb pressure in the star. In the stable equilibrium configurations, therefore, a loss in stellar mass (energy) density occurs for higher values of the angular frequency. The additional energy is radiated in the form of electrical energy. The stellar radius is also decreased so that the star does not necessarily becomes more compact.
10
Nayak, S. N., P. K. Parida, and P. K. Panda. "Effects of the cosmological constant on compact star in quark-meson coupling model." International Journal of Modern Physics E 24, no. 10 (October 2015): 1550068. http://dx.doi.org/10.1142/s0218301315500688.
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We study effect of the cosmological constant on compact star with equation of state provided by quark-meson coupling (QMC) model. In this model, baryons are described as a system of nonoverlapping bags interacting through the scalar and vector mesons. We derive the Tolman–Oppenheimer–Volkoff (TOV) equation taking into account the cosmological constant in static and spherically symmetric metric. Using the equation of state given by QMC model, the mass–radius relationship of the compact star has been computed for various values of the cosmological constant.
11
Ghoroku, Kazuo, Kouki Kubo, Motoi Tachibana, and Fumihiko Toyoda. "Holographic cold nuclear matter and neutron star." International Journal of Modern Physics A 29, no. 10 (April 15, 2014): 1450060. http://dx.doi.org/10.1142/s0217751x14500602.
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We have previously found a new phase of cold nuclear matter based on a holographic gauge theory, where baryons are introduced as instanton gas in the probe [Formula: see text] branes. In our model, we could obtain the equation of state (EOS) of our nuclear matter by introducing Fermi momentum. Then, here we apply this model to the neutron star and study its mass and radius by solving the Tolman–Oppenheimer–Volkoff (TOV) equations in terms of the EOS given here. We give some comments for our holographic model from a viewpoint of the other field theoretical approaches.
12
Vartanyan, Yu L., A. K. Grigoryan, and H. A. Shahinyan. "STRANGE STARS AT VACUUM PRESSURE DEPENDENT ON QUARK DENSITY." Proceedings of the YSU A: Physical and Mathematical Sciences 51, no. 1 (242) (April 17, 2017): 71–76. http://dx.doi.org/10.46991/pysu:a/2017.51.1.071.
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Equation of state of strange quark matter has been studied in the framework of MIT bag model, when vacuum pressure $B$ depends on concentration of baryons $n$. The actuality of such studies is conditioned by the increasing of quark matter density from surface to star center. In the literature there exist different representations of function $B(n)$. In the present work Gaussian parametrization is used, which is based on the idea of existence of asymptotic limiting value of this parameter. For four groups of parameters the equations of state of quark matter were determined. The main integral parameters of star configurations were obtained by numerically integrating of star equilibrium equations (the TOV equation). In the considered case it turns that when vacuum pressure dependence on concentration of baryons is taken into account, configurations of strange stars have maximal masses less than two solar masses.
Erratum: Proc. YSU A: Phys. Math. Sci. 52 (2018), 68
13
Andrew, Keith, Eric V. Steinfelds, and Kristopher A. Andrew. "Cold Quark–Gluon Plasma EOS Applied to a Magnetically Deformed Quark Star with an Anomalous Magnetic Moment." Universe 8, no. 7 (June 27, 2022): 353. http://dx.doi.org/10.3390/universe8070353.
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We consider a QCD cold-plasma-motivated Equation of State (EOS) to examine the impact of an Anomalous Magnetic Moment (AMM) coupling and small shape deformations on the static oblate and prolate core shapes of quark stars. Using the Fogaça QCD-motivated EOS, which shifts from the high-temperature, low-chemical-potential quark–gluon plasma environment to the low-temperature, high-chemical-potential quark stellar core environment, we consider the impact of an AMM coupling with a metric-induced shape deformation parameter in the Tolman–Oppenheimer–Volkov (TOV) equations. The AMM coupling includes a phenomenological scaling that accounts for the weak and strong field characteristics in dense matter. The EOS is developed using a hard gluon and soft gluon decomposition of the gluon field tensor and using a mean-field effective mass for the gluons. The AMM is considered using the Dirac spin tensor coupled to the EM field tensor with quark-flavor-based magnetic moments. The shape parameter is introduced in a metric ansatz that represents oblate and prolate static stellar cores for modified TOV equations. These equations are numerically solved for the final mass and radius states, representing the core collapse of a massive star with a phase transition leading to an unbound quark–gluon plasma. We find that the combined shape parameter and AMM effects can alter the coupled EOS–TOV equations, resulting in an increase in the final mass and a decrease in the final equatorial radius without collapsing the core into a black hole and without violating causality constraints; we find maximum mass values in the range 1.6 Mʘ < M < 2.5 Mʘ. These states are consistent with some astrophysical, high-mass magnetar/pulsar and gravity wave systems and may provide evidence for a core that has undergone a quark–gluon phase transition such as PSR 0943 + 10 and the secondary from the GW 190814 event.
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SHARMA, R., S. KARMAKAR, and S. MUKHERJEE. "MAXIMUM MASS OF A CLASS OF COLD COMPACT STARS." International Journal of Modern Physics D 15, no. 03 (March 2006): 405–18. http://dx.doi.org/10.1142/s0218271806008012.
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We calculate the maximum mass of the class of compact stars described by the Vaidya–Tikekar27 model. The model permits a simple method of systematically fixing bounds on the maximum possible mass of cold compact stars with a given value of radius or central density or surface density. The relevant equations of state are also determined. Although simple, the model is capable of describing the general features of the recently observed very compact stars. For the calculation, no prior knowledge of the equation of state (EOS) is required. This is in contrast to earlier calculations for maximum mass which were done by choosing first the relevant EOSs and using those to solve the TOV equation with appropriate boundary conditions. The bounds obtained by us are comparable and, in some cases, more restrictive than the earlier results.
15
Das, Shyam, Nayan Sarkar, Monimala Mondal, and Farook Rahaman. "A new model for dark matter fluid sphere." Modern Physics Letters A 35, no. 34 (September 7, 2020): 2050280. http://dx.doi.org/10.1142/s0217732320502806.
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We develop a new model for a spherically symmetric dark matter fluid sphere containing two regions: (i) Isotropic inner region with constant density and (ii) Anisotropic outer region. We solve the system of field equation by assuming a particular density profile along with a linear equation of state. The obtained solutions are well-behaved and physically acceptable which represent equilibrium and stable matter configuration by satisfying the Tolman–Oppenheimer–Volkoff (TOV) equation and causality condition, condition on adiabatic index, Harrison–Zeldovich–Novikov criterion, respectively. We consider the compact star EXO 1785-248 (Mass [Formula: see text] and radius R[Formula: see text]8.8 km) to analyze our solutions by graphical demonstrations.
16
Hanifa, M. D. Danarianto, and A. Sulaksono. "Energy Momentum Squared Gravity in Doneva-Jazadjiev anisotropic pressure model of non-rotating neutron stars." Journal of Physics: Conference Series 2214, no. 1 (February 1, 2022): 012003. http://dx.doi.org/10.1088/1742-6596/2214/1/012003.
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Abstract We implement the Doneva-Yazadjiev (DY) anisotropic model of neutron stars into Energy Momentum Squared Gravity (EMSG) theory. We have shown that the Tolmann-Oppenheimer-Volkoff (TOV) equation within this model can be expressed in the terms of effective pressure and energy density. The structure of neutron stars (NS) is then calculated by using Basic Standard Parameter equation of state with hyperons in the center. We found that the combined model is able to adjust the mass-radius relation of the NS. We also found that this model could affect boundary limit of EMSG parameter, α, in the term of stability.
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SARANGI, S., P. K. PANDA, S. K. SAHU, and L. MAHARANA. "ASYMMETRIC NUCLEAR MATTER: A VARIATIONAL APPROACH." International Journal of Modern Physics B 22, no. 25n26 (October 20, 2008): 4524–37. http://dx.doi.org/10.1142/s0217979208050279.
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We discuss here a self-consistent method to calculate the properties of the cold asymmetric nuclear matter. In this model, the nuclear matter is dressed with s-wave pion pairs and the nucleon-nucleon (N-N) interaction is mediated by these pion pairs, ω and ρ mesons. The parameters of these interactions are calculated self-consistently to obtain the saturation properties like equilibrium binding energy, pressure, compressibility and symmetry energy. The computed equation of state is then used in the Tolman-Oppenheimer-Volkoff (TOV) equation to study the mass and radius of a neutron star in the pure neutron matter limit.
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Sarkar, Nayan, Susmita Sarkar, Farook Rahaman, and Ksh Newton Singh. "Anisotropic compact stars model with generalized Bardeen–Hayward mass function." Modern Physics Letters A 36, no. 26 (August 30, 2021): 2150190. http://dx.doi.org/10.1142/s021773232150190x.
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A new compact stars nonsingular model is presented with the generalized Bardeen–Hayward mass function. Generalized Bardeen–Hayward described the regular black hole, however, due to its regularity or nonsingular nature we were inspired to construct an anisotropic compact stars model. Along with the ansatz mass function, we coupled it with a linear equation of state (EoS) to find the solutions of field equations. Indeed, the new solutions are physically viable in all physical ground. The energy conditions and Tolman–Oppenheimer–Volkoff (TOV)-equation are well satisfied signifying that the mass distribution is physically possible and at equilibrium. Also, the static stability criterion, the causality condition and Abreu’s stability condition hold good and therefore configurations are physically static stable. The same condition is further supported by the condition that the adiabatic index, which is greater than the Newtonian limit, i.e. [Formula: see text]. It is also noticed that the bag constant [Formula: see text] is proportional to the surface density in our model.
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Supriyadi, Izrul, Widya Sawitar, Esmar Budi, and Riser Fahdiran. "MODEL MATERI GELAP DUA FLUIDA STATIS DENGAN TAMBAHAN KONSTANTA KOSMOLOGI." Spektra: Jurnal Fisika dan Aplikasinya 3, no. 2 (August 21, 2018): 127–32. http://dx.doi.org/10.21009/spektra.032.07.
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Abstrak
Pada persamaan medan gravitasi Einstein terdapat konstanta kosmologi sebagai konstanta alam yang menjelaskan model mengembangnya alam semesta dan yang paling dominan terdapat di jagad raya ini adalah dalam bentuk energi gelap (dark energy). Kami meninjau model objek dua fluida tidak terkopel, seperti layaknya materi gelap (dark matter) atau bintang yang memiliki karakteristik tensor energi-momentum dan kecepatan-4 nya yang berbeda serta bersifat anisotropik, kemudian disatukan sebagai model dua fluida untuk ditinjau persamaan TOV (Tolman-Oppenheimer-Volkoff) dan persamaan geodesiknya dalam menunjukkan sifat gerak dan model dua fluida tersebut. Hasil perhitungan menunjukkan bahwa model ini dapat menjelaskan persamaan potensial efektif dengan tambahan konstanta kosmologi sebagai karakteristik gerak dan kecepatan tangensial partikel uji dalam orbit lingkaran stabil.
Kata-kata kunci: konstanta kosmologi, anisotropik, potensial efektif, kecepatan tangensial.
Abstract
In Einstein's gravitational field equation has been found the cosmological constant as the natural constant that describes the universe's expansion model and the most dominant in the universe is the dark energy form. We review the two objects of fluid models are not coupled, like dark matter or stars which has the different characteristic energy-momentum tensor and four velocities and anisotropic tend, then combined as two-fluid models for TOV (Tolman-Oppenheimer-Volkoff) equation and the geodesic equation to characterize the movement and the two fluid models. The calculation result shows that this model can explain the potential equation with an addition of an effective cosmological constant as the movement characteristic and tangential velocity of a tested particle in a stable circular orbit.
Keywords: cosmological constant, anisotropic, effective potential, tangential velocity.
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Sarkar, Nayan, Susmita Sarkar, Farook Rahaman, Ksh Newton Singh, and Hasrat Hussain Shah. "Anisotropic fluid spheres satisfying the Karmarkar condition." Modern Physics Letters A 34, no. 15 (May 20, 2019): 1950113. http://dx.doi.org/10.1142/s021773231950113x.
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In this paper, we present new physically viable interior solutions of the Einstein field equations for static and spherically symmetric anisotropic compact stars satisfying the Karmarkar condition. For presenting the exact solutions, we provide a new suitable form of one of the metric potential functions. Obtained solutions satisfy all the physically acceptable properties of realistic fluid spheres and hence solutions are well-behaved and representing matter distributions are in equilibrium state and potentially stable by satisfying the TOV equation and the condition on stability factor, adiabatic indices. We analyze the solutions for two well-known compact stars Vela X-1 (Mass = 1.77 M[Formula: see text], R = 9.56 km) and Cen X-3 (Mass = 1.49 M[Formula: see text], R = 9.17 km).
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Mathias, Amos V., and Jefta M. Sunzu. "A Well-Behaved Anisotropic Strange Star Model." Advances in Mathematical Physics 2022 (November 18, 2022): 1–11. http://dx.doi.org/10.1155/2022/7243750.
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We obtain a new nonsingular exact model for compact stellar objects by using the Einstein field equations. The model is consistent with stellar star with anisotropic quark matter in the absence of electric field. Our treatment considers spacetime geometry which is static and spherically symmetric. Ansatz of a rational form of one of the gravitational potentials is made to generate physically admissible results. The balance of gravitational, hydrostatic, and anisotropic forces within the stellar star is tested by analysing the Tolman-Oppenheimer-Volkoff (TOV) equation. Several stellar objects with masses and radii comparable with observations found in the past are generated. Our model obeys different stability tests and energy conditions. The profiles for the potentials, matter variables, stability, and energy conditions are well behaved.
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Mondal, S. H., M. Alam, M. Hasan, and Md A. Khan. "TOV equation of state and bulk properties of astro-nuclear objects: an investigation." Journal of Physics: Conference Series 2349, no. 1 (September 1, 2022): 012025. http://dx.doi.org/10.1088/1742-6596/2349/1/012025.
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This study of the common characteristics of compact celestial bodies is mostly inspired by the Potekhin group’s current findings on the evolution and structure of compact objects, exploiting the unified equation of state (EoS), proposed by the group reported as Brussels -Montreal (B-M) group. We used three parametric approaches to solve the TOV EoS numerically and obtain number density of baryon, internal stellar pressure, bulk coefficients, and some other quantities for a broad spectrum of mass densities. Numerically simulated results of these quantities are reported in terms of matter density in a tabular form. A schematic view of calculated quantities and their comparison with reference values wherever available are reported in the representative cases.
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Pender, Jamol, Richard Rand, and Elizabeth Wesson. "A Stochastic Analysis of Queues with Customer Choice and Delayed Information." Mathematics of Operations Research 45, no. 3 (August 2020): 1104–26. http://dx.doi.org/10.1287/moor.2019.1024.
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Many service systems provide queue length information to customers, thereby allowing customers to choose among many options of service. However, queue length information is often delayed, and it is often not provided in real time. Recent work by Dong et al. [Dong J, Yom-Tov E, Yom-Tov GB (2018) The impact of delay announcements on hospital network coordination and waiting times. Management Sci. 65(5):1969–1994.] explores the impact of these delays in an empirical study in U.S. hospitals. Work by Pender et al. [Pender J, Rand RH, Wesson E (2017) Queues with choice via delay differential equations. Internat. J. Bifurcation Chaos Appl. Sci. Engrg. 27(4):1730016-1–1730016-20.] uses a two-dimensional fluid model to study the impact of delayed information and determine the exact threshold under which delayed information can cause oscillations in the dynamics of the queue length. In this work, we confirm that the fluid model analyzed by Pender et al. [Pender J, Rand RH, Wesson E (2017) Queues with choice via delay differential equations. Internat. J. Bifurcation Chaos Appl. Sci. Engrg. 27(4):1730016-1–1730016-20.] can be rigorously obtained as a functional law of large numbers limit of a stochastic queueing process, and we generalize their threshold analysis to arbitrary dimensions. Moreover, we prove a functional central limit theorem for the queue length process and show that the scaled queue length converges to a stochastic delay differential equation. Thus, our analysis sheds new insight on how delayed information can produce unexpected system dynamics.
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Shee, Dibyendu, Debabrata Deb, Shounak Ghosh, Saibal Ray, and B. K. Guha. "Anisotropic strange star with Tolman V potential." International Journal of Modern Physics D 27, no. 08 (May 30, 2018): 1850089. http://dx.doi.org/10.1142/s021827181850089x.
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In this paper, we present a strange stellar model using Tolman [Formula: see text]-type metric potential employing simplest form of the MIT bag equation of state (EOS) for the quark matter. We consider that the stellar system is spherically symmetric, compact and made of an anisotropic fluid. Choosing different values of [Formula: see text] we obtain exact solutions of the Einstein field equations and finally conclude that for a specific value of the parameter [Formula: see text], we find physically acceptable features of the stellar object. Further, we conduct different physical tests, viz., the energy condition, generalized Tolman–Oppeheimer–Volkoff (TOV) equation, Herrera’s cracking concept, etc., to confirm the physical validity of the presented model. Matching conditions provide expressions for different constants whereas maximization of the anisotropy parameter provides bag constant. By using the observed data of several compact stars, we derive exact values of some of the physical parameters and exhibit their features in tabular form. It is to note that our predicted value of the bag constant satisfies the report of CERN-SPS and RHIC.
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DAS, C., P. K. PANDA, and M. ADHIKARY. "PROPERTIES OF HOT NEUTRON STAR." International Journal of Modern Physics D 12, no. 07 (August 2003): 1241–54. http://dx.doi.org/10.1142/s0218271803003608.
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The properties of neutron star at temperatures 5 MeV, 10 MeV and 15 MeV are calculated by solving Tolmann–Oppenheimer–Volkoff (TOV) equation. The required equation of state of pure neutron matter is obtained using density dependent Sussex interaction. It is observed that maximum stable mass of the star corresponds to minimum gravitational radius for a given equation of state. Just like the limiting mass, limiting value of redshift, moment of inertia, Kepler frequency as well as Kepler period are observed in case of the neutron star. It is found that the star become somewhat 'massive' and 'fat' at higher temperatures. With the increase in temperature the moment of inertia and Kepler rotational period increase but redshift decreases and Kepler frequency slows down. We also predict that there is a possibility of pion condensation in pure neutron matter.
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Spieksma, F. M. "COUNTABLE STATE MARKOV PROCESSES: NON-EXPLOSIVENESS AND MOMENT FUNCTION." Probability in the Engineering and Informational Sciences 29, no. 4 (July 9, 2015): 623–37. http://dx.doi.org/10.1017/s0269964815000224.
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The existence of a moment function satisfying a drift function condition is well known to guarantee non-explosiveness of the associated minimal Markov process (cf. [1,9]), under standard technical conditions. Surprisingly, the reverse is true as well for a countable space Markov process. We prove this result by showing that recurrence of an associated jump process, that we call the α-jump process, is equivalent to non-explosiveness. Non-explosiveness corresponds in a natural way to the validity of the Kolmogorov integral relation for the function identically equal to 1. In particular, we show that positive recurrence of the α-jump chain implies that all bounded functions satisfy the Kolmogorov integral relation. We present a drift function criterion characterizing positive recurrence of this α-jump chain.Suppose that to a drift functionVthere corresponds another drift functionW, which is a moment with respect toV. Via a transformation argument, the above relations hold for the transformed process with respect toV. Transferring the results back to the original process, allows to characterize theV-bounded functions that satisfy the Kolmogorov forward equation.
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Aziz, Abdul, Saibal Ray, Farook Rahaman, M. Khlopov, and B. K. Guha. "Constraining values of bag constant for strange star candidates." International Journal of Modern Physics D 28, no. 13 (October 2019): 1941006. http://dx.doi.org/10.1142/s0218271819410062.
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We provide a strange star model under the framework of general relativity by using a general linear equation of state (EOS). The solution set thus obtained is employed on altogether 20 compact star candidates to constraint values of MIT bag model. No specific value of the bag constant ([Formula: see text]) a priori is assumed, rather possible range of values for bag constant is determined from observational data of the said set of compact stars. To do so, the Tolman–Oppenheimer–Volkoff (TOV) equation is solved by homotopy perturbation method (HPM) and hence we get a mass function for the stellar system. The solution to the Einstein field equations represents a nonsingular, causal and stable stellar structure which can be related to strange stars. Eventually, we get an interesting result on the range of the bag constant as [Formula: see text]. We have found the maximum surface redshift [Formula: see text] and shown that the central redshift ([Formula: see text]) cannot have value larger than [Formula: see text], where [Formula: see text]. Also, we provide a possible value of bag constant for neutron star with quark core using hadronic as well as quark EOS.
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Chowdhury, Sourav Roy, Debabrata Deb, Farook Rahaman, Saibal Ray, and B. K. Guha. "Anisotropic strange star inspired by Finsler geometry." International Journal of Modern Physics D 29, no. 01 (January 2020): 2050001. http://dx.doi.org/10.1142/s0218271820500017.
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In this paper, we report on a study of the anisotropic strange stars under Finsler geometry. Keeping in mind that Finsler spacetime is not merely a generalization of Riemannian geometry rather the main idea is the projectivized tangent bundle of the manifold [Formula: see text], we have developed the respective field equations. Thereafter, we consider the strange quark distribution inside the stellar system followed by the MIT bag model equation-of-state (EoS). To find out the stability and also the physical acceptability of the stellar configuration, we perform in detail some basic physical tests of the proposed model. The results of the testing show that the system is consistent with the Tolman–Oppenheimer–Volkoff (TOV) equation, Herrera cracking concept, different energy conditions and adiabatic index. One important result that we observe is, the anisotropic stress reaches the maximum at the surface of the stellar configuration. We calculate (i) the maximum mass as well as the corresponding radius, (ii) the central density of the strange stars for finite values of bag constant [Formula: see text] and (iii) the fractional binding energy of the system. This study shows that Finsler geometry is especially suitable to explain massive stellar systems.
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Li, A., Z.-Q. Miao, J.-L. Jiang, S.-P. Tang, and R.-X. Xu. "Bayesian inference of quark star equation of state using the NICER PSR J0030+0451 data." Monthly Notices of the Royal Astronomical Society 506, no. 4 (July 16, 2021): 5916–22. http://dx.doi.org/10.1093/mnras/stab2029.
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ABSTRACT We constrain the equation of state of quark stars within the Bayesian statistical approach using the mass and radius measurements of PSR J0030+0451 from NICER. Three types of bag models, with and without non-zero finite quark mass and/or superfluidity, are employed for quark stars made up with self-bound strange quark matter. We find the $90{{\ \rm per\ cent}}$ posterior credible boundary around the most probable values of the quark star maximum mass is $M_{\rm TOV}=2.38_{-0.23}^{+0.26}\, M_{\odot }$, within the model flexibility of the finite quark mass, the quark pairing gap, and the perturbative contribution from the one-gluon exchange. The radius of a canonical $1.4 \, M_{\odot }$ quark star is $R_{\rm 1.4}\sim 12.3\, {\rm km}$, smaller than the results based on neutron star models.
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Ayriyan, Alexander, Ján Buša, Hovik Grigorian, and Gevorg Poghosyan. "Parallel Algorithm for Solving TOV Equations for Sequence of Cold and Dense Nuclear Matter Models." EPJ Web of Conferences 177 (2018): 07001. http://dx.doi.org/10.1051/epjconf/201817707001.
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We have introduced parallel algorithm simulation of neutron star configurations for set of equation of state models. The performance of the parallel algorithm has been investigated for testing set of EoS models on two computational systems. It scales when using with MPI on modern CPUs and this investigation allowed us also to compare two different types of computational nodes.
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BAO, G., E. ØSTGAARD, and B. DYBVIK. "EQUATION OF STATE, MASS, RADIUS, MOMENT OF INERTIA, AND SURFACE GRAVITATIONAL REDSHIFT FOR NEUTRON STARS." International Journal of Modern Physics D 03, no. 04 (December 1994): 813–38. http://dx.doi.org/10.1142/s0218271894000903.
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We have calculated total masses and radii of neutron stars from the Tolman-Oppenheimer-Volkoff (TOV) equations (for matter in equilibrium in gravitational fields) and different equations of state for neutron-star matter. The calculations are done for different input central densities. We have also obtained pressure and density as functions of distance from the centre of the star, and moments of inertia and surface gravitational redshifts as functions of the total mass of the star. The maximum mass M max is for all equations of state in our calculations given by 1.65M⊙<M max <2.43M⊙ (where M⊙ is the solar mass), which agrees very well with “experimental” results. Corresponding radii R are given by 8.8 km <R<12.7 km , and a smaller central density will, in general, give a smaller mass and a larger radius.
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Soma, Shriya, Lingxiao Wang, Shuzhe Shi, Horst Stöcker, and Kai Zhou. "Neural network reconstruction of the dense matter equation of state from neutron star observables." Journal of Cosmology and Astroparticle Physics 2022, no. 08 (August 1, 2022): 071. http://dx.doi.org/10.1088/1475-7516/2022/08/071.
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Abstract The Equation of State (EoS) of strongly interacting cold and hot ultra-dense QCD matter remains a major challenge in the field of nuclear astrophysics. With the advancements in measurements of neutron star masses, radii, and tidal deformabilities, from electromagnetic and gravitational wave observations, neutron stars play an important role in constraining the ultra-dense QCD matter EoS. In this work, we present a novel method that exploits deep learning techniques to reconstruct the neutron star EoS from mass-radius (M-R) observations. We employ neural networks (NNs) to represent the EoS in a model-independent way, within the range of ∼1-7 times the nuclear saturation density. The unsupervised Automatic Differentiation (AD) framework is implemented to optimize the EoS, so as to yield through TOV equations, an M-R curve that best fits the observations. We demonstrate that this method works by rebuilding the EoS on mock data, i.e., mass-radius pairs derived from a randomly generated polytropic EoS. The reconstructed EoS fits the mock data with reasonable accuracy, using just 11 mock M-R pairs observations, close to the current number of actual observations.
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Ashraf, Asifa, and Zhiyue Zhang. "Stable wormhole models in general relativity under conformal symmetry." International Journal of Geometric Methods in Modern Physics 18, no. 03 (January 18, 2021): 2150041. http://dx.doi.org/10.1142/s0219887821500419.
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In this study, we shall explore conformal symmetry to examine the wormhole models by considering traceless fluid. In this regard, we shall take anisotropic fluid with spherically symmetric space-time. Further, we shall calculate the properties of shape-functions, which are necessary for the existence of wormhole geometry. The presence of exotic matter is confirmed in all the cases through the violation of the Null Energy Condition. Furthermore, we have discussed the stability of wormhole solutions through the Tolman–Oppenheimer–Volkoff (TOV) equation. It is observed that our acquired solutions are stable under the particular values of involved parameters in different cases in conformal symmetry.
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Holmbeck, Erika M., Richard O’Shaughnessy, Vera Delfavero, and Krzysztof Belczynski. "A Nuclear Equation of State Inferred from Stellar r-process Abundances." Astrophysical Journal 926, no. 2 (February 1, 2022): 196. http://dx.doi.org/10.3847/1538-4357/ac490e.
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Abstract Binary neutron star mergers (NSMs) have been confirmed as one source of the heaviest observable elements made by the rapid neutron-capture (r-) process. However, modeling NSM outflows—from the total ejecta masses to their elemental yields—depends on the unknown nuclear equation of state (EOS) that governs neutron star structure. In this work, we derive a phenomenological EOS by assuming that NSMs are the dominant sources of the heavy element material in metal-poor stars with r-process abundance patterns. We start with a population synthesis model to obtain a population of merging neutron star binaries and calculate their EOS-dependent elemental yields. Under the assumption that these mergers were responsible for the majority of r-process elements in the metal-poor stars, we find parameters representing the EOS for which the theoretical NSM yields reproduce the derived abundances from observations of metal-poor stars. For our proof-of-concept assumptions, we find an EOS that is slightly softer than, but still in agreement with, current constraints, e.g., by the Neutron Star Interior Composition Explorer, with R 1.4 = 12.25 ± 0.03 km and M TOV = 2.17 ± 0.03 M ⊙ (statistical uncertainties, neglecting modeling systematics).
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Farasat Shamir, M., and I. Fayyaz. "Charged stellar structure in Tolman–Kuchowicz spacetime." International Journal of Geometric Methods in Modern Physics 17, no. 09 (August 2020): 2050140. http://dx.doi.org/10.1142/s0219887820501406.
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In this paper, we have presented the Einstein–Maxwell equations which are described by the spherically symmetric spacetime in the presence of charge by exploiting the Tolman–Kuchowicz spacetime. The corresponding field equations are constructed and the form of charge distribution is chosen to be [Formula: see text], where [Formula: see text] is a constant quantity. We also find the values of unknown constants from junction conditions and discuss the behavior of effective energy density, effective radial and tangential pressure and anisotropic factor with two viable [Formula: see text] models. We examine the physical stability of charged stellar structure through energy conditions, causality and stability condition. We use modified form of TOV equation for anisotropic charged fluid sphere to analyze the equilibrium condition. In this work, we model the compact star candidate SAXJ 1808.4 – 3658 and study the compactness level and anisotropic behavior corresponding to the variation of physical parameters which are involved in [Formula: see text] models. Further, we evaluate some important properties such as mass-radius ratio compactness factor and surface redshift. It is depicted from this study that the obtained solutions provide strong evidences for more realistic and viable stellar model.
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Mustafa, G., and Tie-Cheng Xia. "Embedded class solutions of an anisotropic object in Rastall gravity." International Journal of Modern Physics A 35, no. 21 (July 27, 2020): 2050109. http://dx.doi.org/10.1142/s0217751x20501092.
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In this current work, we explore an anisotropic compact model with radius 9.1 km and mass 2.01 [Formula: see text] in the regime of Karmarkar condition in Rastall theory. To solve the extended field equations for the Rastall framework we have employed the Karmarkar condition. We investigate a comparative discussion to show the physical acceptance of Karmarkar condition in Rastall theory. Our obtained solutions, i.e. metric functions, density function and both the pressure components have well-behaved nature. The energy bounds and the equilibrium stability in the background of modified TOV equation (for Rastall proposal) are also discussed in this study. The parameter [Formula: see text] from [Formula: see text] metric function has some important role in this current model. All the calculated properties have different natures for [Formula: see text] to [Formula: see text]. In this current study we also discuss some physical parameters of this current model to check the validity of the model. In the end, it is concluded that our model is acceptable physically and geometrically.
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Gedela, Satyanarayana, Ravindra K. Bisht, and Neeraj Pant. "Relativistic modeling of stellar objects using embedded class one spacetime continuum." Modern Physics Letters A 35, no. 13 (February 7, 2020): 2050097. http://dx.doi.org/10.1142/s0217732320500972.
Full textAbstract:
In this paper, we explore a family of exact solutions to the Einstein field equations (EFEs) describing a spherically symmetric, static distribution of fluid spheres with pressure anisotropy in the setting of embedding class one spacetime continuum. A detailed theoretical analysis of this class of solutions for compact stars PSR J16142230, Her X-1, LMC X-4 and 4U 1538-52 is carried out. The solutions are verified by examining various physical aspects, viz., anisotropy, gravitational redshift, causality condition, equilibrium (TOV-equation), stable static criterion and energy conditions, in connection to their cogency. Due to the well-behaved nature of the solutions for a large range of positive real [Formula: see text] values, we develop models of above stellar objects and discuss their behavior with graphical representations of the class of solutions of the first two objects extensively. The solutions studied by Fuloria [Astrophys. Space Sci. 362, 217 (2017)] for [Formula: see text] and Tamta and Fuloria [Mod. Phys. Lett. A 34, 2050001 (2019), https://doi.org/10.1142/S0217732320500017 ] for [Formula: see text] are particular cases of our generalized solution.
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Boonserm, Petarpa. "The Modified Tolman-Oppenheimer-Volkov (TOV) Equation and the Effect of Charge on Pressure in Charge Anisotropy." American Journal of Physics and Applications 4, no. 2 (2016): 57. http://dx.doi.org/10.11648/j.ajpa.20160402.14.
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Shamir, M. Farasat, and I. Fayyaz. "Charged anisotropic compact stars in Logarithmic-Corrected R2 gravity." International Journal of Modern Physics A 35, no. 04 (February 10, 2020): 2050013. http://dx.doi.org/10.1142/s0217751x2050013x.
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We consider [Formula: see text] corrected model, i.e. [Formula: see text], where [Formula: see text] is the Ricci scalar and [Formula: see text], [Formula: see text] are arbitrary constant values, to investigate some of the interior configurations of static anisotropic spherical charged stellar structures. The existence of electric charge and a strong electric field confirms due to the higher values of pressure distribution and energy density of the matter inside the stars. Furthermore, for compact star configurations, we also consider the simplified MIT bag model equation of state (EoS) given by [Formula: see text], where [Formula: see text] is radial pressure, [Formula: see text] is energy density and [Formula: see text] is bag constant. This approach allows to find electric charge from the Einstein–Maxwell field equations. We have extensively discussed the behavior of the electric charge and anisotropic fluid distribution factor for five different values of [Formula: see text]. Interestingly, it is noticed during this study, for smaller values of [Formula: see text] we get intensity in electric charge. The Tolman–Oppenheimer–Volkoff equation (TOV), is modified in order to carry electric charge. In particular, we model the compact star candidates SAXJ 1808.4–3658 and Vela X-1 and give graphical representation of some important properties such as equilibrium condition, mass-radius ratio and surface redshift. In the end, our calculated solutions provide strong evidences for more realistic and viable charged stellar model.
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Hassan, Zinnat, Ghulam Mustafa, and Pradyumn Kumar Sahoo. "Wormhole Solutions in Symmetric Teleparallel Gravity with Noncommutative Geometry." Symmetry 13, no. 7 (July 14, 2021): 1260. http://dx.doi.org/10.3390/sym13071260.
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This article describes the study of wormhole solutions in f(Q) gravity with noncommutative geometry. Here, we considered two different f(Q) models—a linear model f(Q)=αQ and an exponential model f(Q)=Q−α1−e−Q, where Q is the non-metricity and α is the model parameter. In addition, we discussed the existence of wormhole solutions with the help of the Gaussian and Lorentzian distributions of these linear and exponential models. We investigated the feasible solutions and graphically analyzed the different properties of these models by taking appropriate values for the parameter. Moreover, we used the Tolman–Oppenheimer–Volkov (TOV) equation to check the stability of the wormhole solutions that we obtained. Hence, we found that the wormhole solutions obtained with our models are physically capable and stable.
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Lim, Yeunhwan, Chang Ho Hyun, Kyujin Kwak, and Chang-Hwan Lee. "Hyperon puzzle of neutron stars with Skyrme force models." International Journal of Modern Physics E 24, no. 12 (December 2015): 1550100. http://dx.doi.org/10.1142/s0218301315501001.
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We consider the so-called hyperon puzzle of neutron star (NS). We employ Skyrme force models for the description of in-medium nucleon–nucleon (NN), nucleon–Lambda hyperon ([Formula: see text]) and Lambda–Lambda ([Formula: see text]) interactions. A phenomenological finite-range force (FRF) for the [Formula: see text] interaction is considered as well. Equation of state (EoS) of NS matter is obtained in the framework of density functional theory, and Tolman–Oppenheimer–Volkoff (TOV) equations are solved to obtain the mass-radius relations of NSs. It has been generally known that the existence of hyperons in the NS matter is not well supported by the recent discovery of large-mass NSs ([Formula: see text]) since hyperons make the EoS softer than the one without them. For the selected interaction models, [Formula: see text] interactions reduce the maximum mass of NS by about 30%, while [Formula: see text] interactions can give about 10% enhancement. Consequently, we find that some Skyrme force models predict the maximum mass of NS consistent with the observation of [Formula: see text] NSs, and at the same time satisfy observationally constrained mass-radius relations.
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ROCHA, A. S. S., C. A. Z. VASCONCELLOS, and F. FERNÁNDEZ. "A FUZZY BAG MODEL FOR NUCLEAR MATTER: A PRELIMINARY APPROACH." International Journal of Modern Physics D 19, no. 08n10 (August 2010): 1593–97. http://dx.doi.org/10.1142/s0218271810017354.
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In this work we develop an effective formalism for nuclear matter based on the fuzzy bag model. The main objective of our study is to discuss the feasibility of using the fuzzy bag model to describe nuclear matter properties. The physical system is described in our approach by an internal energy function, which has a free term, corresponding to a free Fermi gas, and an interacting one. In the interacting part, pion exchange is taken into account via an effective potential. To avoid superposition of nucleons, we introduce an exclusion volume à la Van der Waals. The internal energy function depends on the nuclear matter density and also on a parameter which will determine the expected volume of a nucleon in matter. We then obtain results for the binding energy per nucleon for the symmetric nuclear matter and for neutron matter, as well as the equation of state within this model. We then determine the mass of neutron stars in hydrostatic equilibrium, using the TOV equations. In spite of utilizing a treatment that is still very preliminary, our results show the feasibility of using this treatment to describe nuclear matter properties.
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Most, Elias R., L. Jens Papenfort, Lukas R. Weih, and Luciano Rezzolla. "A lower bound on the maximum mass if the secondary in GW190814 was once a rapidly spinning neutron star." Monthly Notices of the Royal Astronomical Society: Letters 499, no. 1 (September 24, 2020): L82—L86. http://dx.doi.org/10.1093/mnrasl/slaa168.
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ABSTRACT The recent detection of GW190814 featured the merger of a binary with a primary having a mass of $\sim 23\, \mathrm{ M}_{\odot }$ and a secondary with a mass of $\sim 2.6\, \mathrm{ M}_{\odot }$. While the primary was most likely a black hole, the secondary could be interpreted as either the lightest black hole or the most massive neutron star ever observed, but also as the indication of a novel class of exotic compact objects. We here argue that although the secondary in GW190814 is most likely a black hole at merger, it needs not be an ab-initio black hole nor an exotic object. Rather, based on our current understanding of the nuclear-matter equation of state, it can be a rapidly rotating neutron star that collapsed to a rotating black hole at some point before merger. Using universal relations connecting the masses and spins of uniformly rotating neutron stars, we estimate the spin, $0.49_{-0.05}^{+0.08} \lesssim \chi \lesssim 0.68_{-0.05}^{+0.11}$, of the secondary – a quantity not constrained so far by the detection – and a novel strict lower bound on the maximum mass, $M_{_{\mathrm{TOV}}}\gt 2.08^{+0.04}_{-0.04}\, \, \mathrm{ M}_{\odot }$ and an optimal bound of $M_{_{\mathrm{TOV}}}\gt 2.15^{+0.04}_{-0.04}\, \, \mathrm{ M}_{\odot }$, of non-rotating neutron stars, consistent with recent observations of a very massive pulsar. The new lower bound also remains valid even in the less likely scenario in which the secondary neutron star never collapsed to a black hole.
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Margalit, Ben, Adam S. Jermyn, Brian D. Metzger, Luke F. Roberts, and Eliot Quataert. "Angular-momentum Transport in Proto-neutron Stars and the Fate of Neutron Star Merger Remnants." Astrophysical Journal 939, no. 1 (November 1, 2022): 51. http://dx.doi.org/10.3847/1538-4357/ac8b01.
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Abstract Both the core collapse of rotating massive stars, and the coalescence of neutron star (NS) binaries result in the formation of a hot, differentially rotating NS remnant. The timescales over which differential rotation is removed by internal angular-momentum transport processes (viscosity) have key implications for the remnant’s long-term stability and the NS equation of state (EOS). Guided by a nonrotating model of a cooling proto-NS, we estimate the dominant sources of viscosity using an externally imposed angular-velocity profile Ω(r). Although the magneto-rotational instability provides the dominant source of effective viscosity at large radii, convection and/or the Tayler–Spruit dynamo dominate in the core of merger remnants where dΩ/dr ≥ 0. Furthermore, the viscous timescale in the remnant core is sufficiently short that solid-body rotation will be enforced faster than matter is accreted from rotationally supported outer layers. Guided by these results, we develop a toy model for how the merger remnant core grows in mass and angular momentum due to accretion. We find that merger remnants with sufficiently massive and slowly rotating initial cores may collapse to black holes via envelope accretion, even when the total remnant mass is less than the usually considered threshold ≈1.2 M TOV for forming a stable solid-body rotating NS remnant (where M TOV is the maximum nonrotating NS mass supported by the EOS). This qualitatively new picture of the post-merger remnant evolution and stability criterion has important implications for the expected electromagnetic counterparts from binary NS mergers and for multimessenger constraints on the NS EOS.
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Jasim, Mahmood Khalid, Sunil Kumar Maurya, Ksh Newton Singh, and Riju Nag. "Anisotropic Strange Star in 5D Einstein-Gauss-Bonnet Gravity." Entropy 23, no. 8 (August 6, 2021): 1015. http://dx.doi.org/10.3390/e23081015.
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In this paper, we investigated a new anisotropic solution for the strange star model in the context of 5D Einstein-Gauss-Bonnet (EGB) gravity. For this purpose, we used a linear equation of state (EOS), in particular pr=βρ+γ, (where β and γ are constants) together with a well-behaved ansatz for gravitational potential, corresponding to a radial component of spacetime. In this way, we found the other gravitational potential as well as main thermodynamical variables, such as pressures (both radial and tangential) with energy density. The constant parameters of the anisotropic solution were obtained by matching a well-known Boulware-Deser solution at the boundary. The physical viability of the strange star model was also tested in order to describe the realistic models. Moreover, we studied the hydrostatic equilibrium of the stellar system by using a modified TOV equation and the dynamical stability through the critical value of the radial adiabatic index. The mass-radius relationship was also established for determining the compactness and surface redshift of the model, which increases with the Gauss-Bonnet coupling constant α but does not cross the Buchdahal limit.
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Nazar, H., and G. Abbas. "Model of Charged Anisotropic Strange Stars in Minimally Coupled f R Gravity." Advances in Astronomy 2021 (January 2, 2021): 1–25. http://dx.doi.org/10.1155/2021/6698208.
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In the present article, we have investigated a new family of nonsingular solutions of static relativistic compact sphere which incorporates the characteristics of anisotropic fluid and electromagnetic field in the context of minimally coupled f R theory of gravity. The strange matter MIT bag model equation of state (EoS) has been considered along with the usual forms of the Karori–Barua KB metric potentials. For this purpose, we derived the Einstein–Maxwell field equations in the assistance of strange matter EoS and KB type ansatz by employing the two viable and cosmologically well-consistent models of f R = R + γ R 2 and f R = R + γ R R + α R 2 . Thereafter, we have checked the physical acceptability of the proposed results such as pressure, energy density, energy conditions, TOV equation, stability conditions, mass function, compactness, and surface redshift by using graphical representation. Moreover, we have investigated that the energy density and radial pressure are nonsingular at the core or free from central singularity and always regular at every interior point of the compact sphere. The numerical values of such parameters along with the surface density, charge to radius ratio, and bag constant are computed for three well-known compact stars such as CS1 SAXJ 1808 . 4 − 3658 ( x ˜ = 7.07 km , CS2 VelaX − 1 x ˜ = 9.56 km , and CS3 4U1820 − 30 x ˜ = 10 km and are presented in Tables 1–6. Conclusively, we have noticed that our presented charged compact stellar object in the background of two well-known f R models obeys all the necessary conditions for the stable equilibrium position and which is also perfectly fit to compose the strange quark star object.
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Momeni, Davood, H. Gholizade, Muhammad Raza, and Ratbay Myrzakulov. "Tolman–Oppenheimer–Volkoff equations in nonlocal f(R) gravity." International Journal of Modern Physics A 30, no. 16 (June 9, 2015): 1550093. http://dx.doi.org/10.1142/s0217751x15500931.
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Nonlocal f(R) gravity was proposed as a powerful alternative to general relativity (GR). This theory has potentially adverse implications for infrared (IR) regime as well as ultraviolet (UV) early epochs. However, there are a lot of powerful features, making it really user-friendly. A scalar–tensor frame comprising two auxiliary scalar fields is used to reduce complex action. However, this is not the case for the modification complex which plays a distinct role in modified theories for gravity. In this work, we study the dynamics of a static, spherically symmetric object. The interior region of space–time had rapidly filled the perfect fluid. However, it is possible to derive a physically based model which relates interior metric to nonlocal f(R). The Tolman–Oppenheimer–Volkoff (TOV) equations would be a set of first-order differential equations from which we can deduce all mathematical (physical) truths and derive all dynamical objects. This set of dynamical equations govern pressure p, density ρ, mass m and auxiliary fields {ψ, ξ}. The full conditional solutions are evaluated and inverted numerically to obtain exact forms of the compact stars Her X-1, SAX J 1808.4-3658 and 4U 1820-30 for nonlocal Starobinsky model of f(◻-1 R) = ◻-1 R+α(◻-1 R)2. The program solves the differential equations numerically using adaptive Gaussian quadrature. An ascription of correctness is supposed to be an empirical equation of state [Formula: see text] for star which is informative in so far as it excludes an alternative nonlocal approach to compact star formation. This model is most suited for astrophysical observation.
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Boonserm, Petarpa, Tritos Ngampitipan, and Matt Visser. "Mimicking static anisotropic fluid spheres in general relativity." International Journal of Modern Physics D 25, no. 02 (February 2016): 1650019. http://dx.doi.org/10.1142/s021827181650019x.
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We argue that an arbitrary general relativistic static anisotropic fluid sphere, (static and spherically symmetric but with transverse pressure not equal to radial pressure), can nevertheless be successfully mimicked by suitable linear combinations of theoretically attractive and quite simple classical matter: a classical (charged) isotropic perfect fluid, a classical electromagnetic field and a classical (minimally coupled) scalar field. While the most general decomposition is not unique, a preferred minimal decomposition can be constructed that is unique. We show how the classical energy conditions for the anisotropic fluid sphere can be related to energy conditions for the isotropic perfect fluid, electromagnetic field, and scalar field components of the model. Furthermore, we show how this decomposition relates to the distribution of both electric charge density and scalar charge density throughout the model. The generalized TOV equation implies that the perfect fluid component in this model is automatically in internal equilibrium, with pressure forces, electric forces, and scalar forces balancing the gravitational pseudo-force. Consequently, we can build theoretically attractive matter models that can be used to mimic almost any static spherically symmetric spacetime.
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Singh, Ksh Newton, Piyali Bhar, Farook Rahaman, Neeraj Pant, and Mansur Rahaman. "Conformally non-flat spacetime representing dense compact objects." Modern Physics Letters A 32, no. 18 (May 22, 2017): 1750093. http://dx.doi.org/10.1142/s0217732317500936.
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A new conformally non-flat interior spacetime embedded in five-dimensional (5D) pseudo Euclidean space is explored in this paper. We proceed our calculation with the assumption of spherically symmetric anisotropic matter distribution and Karmarkar condition (necessary condition for class one). This solution is free from geometrical singularity and well-behaved in all respects. We ansatz a new type of metric potential [Formula: see text] and solve for the metric potential [Formula: see text] via Karmarkar condition. Further, all the physical parameters are determined from Einstein’s field equations using the two metric potentials. All the constants of integration are determined using boundary conditions. Due to its conformally non-flat character, it can represent bounded configurations. Therefore, we have used it to model two compact stars Vela X-1 and Cyg X-2. Indeed, the obtained masses and radii of these two objects from our solution are well matched with those observed values given in [T. Gangopadhyay et al., Mon. Not. R. Astron. Soc. 431, 3216 (2013)] and [J. Casares et al., Mon. Not. R. Astron. Soc. 401, 2517 (2010)]. The equilibrium of the models is investigated from generalized TOV-equation. We have adopted [L. Herrera’s, Phys. Lett. A 165, 206 (1992)] method and static stability criterion of Harisson–Zeldovich–Novikov [B. K. Harrison et al., Gravitational Theory and Gravitational Collapse (University of Chicago Press, 1965); Ya. B. Zeldovich and I. D. Novikov, Relativistic Astrophysics, Vol. 1, Stars and Relativity (University of Chicago Press, 1971)] to analyze the stability of the models.
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Egger, Joseph, and Klaus-Peter Hoinka. "Mountain Torque Events at the Tibetan Plateau." Monthly Weather Review 136, no. 2 (February 1, 2008): 389–404. http://dx.doi.org/10.1175/2007mwr2126.1.
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Abstract The interaction of large-scale wave systems with the Tibetan Plateau (TP) is investigated by regressing pressure, potential temperature, winds, precipitation, and selected fluxes in winter onto the three components Toi of this massif’s mountain torque on the basis of the 40-yr ECMWF reanalysis (ERA-40) data. Events with respect to the equatorial “Greenwich” axis of the global angular momentum exhibit by far the largest torques (To1,), which essentially represent north–south pressure differences across the TP. The axial torque To3 peaks when the surface pressure is high at the eastern slope of the TP. The torque To2 with respect to the 90°E axis is closely related to To3 with To2 ∼ −To3. The maximum (minimum) of To1 tends to occur about 1 day earlier than the minimum (maximum) of To2. All torque events are initiated by equivalent barotropic perturbations moving eastward along the northern rim of the TP. In general, the initial depression, for example, forms a southward-protruding extension at the eastern slope of the TP and a new high grows near Japan. Later, the perturbation near Japan moves eastward in To2 events but extends northward in To1 events. These flow developments cannot be explained by theories of topographic instability. The observed vertical motion at the lee slope is at best partly consistent with theories of linear quasigeostrophic wave motion along mountain slopes. These findings lead the authors to test the eventual usefulness of linear theories by fitting the linear terms of a novel statistical equation for the potential temperature θ to the observed changes of θ and the torque to the observations. This test indicates that the evolving regression patterns of θ can be explained by linear terms at least in specific domains. In turn, pressure tendency regressions at a selected level can be calculated on the basis of the linear θ tendencies above that level. The formation of the lee trough appears to be mainly caused by horizontal warm-air advection along the slopes, but changes of the potential temperature above the height of the TP also contribute significantly to the pressure changes in the lee. Cold-air advection aloft strengthens the Japan high. “Turbulent” transports appear to be mainly responsible for the decay of the perturbations but data accuracy problems impede the analysis. In particular, the noisiness of the vertical motion fields affects the skill of the linear calculations.