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Journal articles on the topic 'Relativistic compact objects'

Author: Grafiati

Published: 18 May 2024

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1

Mizuno, Yosuke. "GRMHD Simulations and Modeling for Jet Formation and Acceleration Region in AGNs." Universe 8, no. 2 (January 28, 2022): 85. http://dx.doi.org/10.3390/universe8020085.

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Relativistic jets are collimated plasma outflows with relativistic speeds. Astrophysical objects involving relativistic jets are a system comprising a compact object such as a black hole, surrounded by rotating accretion flows, with the relativistic jets produced near the central compact object. The most accepted models explaining the origin of relativistic jets involve magnetohydrodynamic (MHD) processes. Over the past few decades, many general relativistic MHD (GRMHD) codes have been developed and applied to model relativistic jet formation in various conditions. This short review provides an overview of the recent progress of GRMHD simulations in generating relativistic jets and their modeling for observations.

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2

Paul, Bikash Chandra, and Rumi Deb. "Relativistic solutions of anisotropic compact objects." Astrophysics and Space Science 354, no. 2 (September 13, 2014): 421–30. http://dx.doi.org/10.1007/s10509-014-2097-2.

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3

Mak, M. K., and T. Harko. "Relativistic compact objects in isotropic coordinates." Pramana 65, no. 2 (August 2005): 185–92. http://dx.doi.org/10.1007/bf02898610.

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4

Mitra, Abhas, and Krishna Kumar Singh. "Thermal Radiation from Compact Objects in Curved Space-Time." Universe 8, no. 10 (September 26, 2022): 504. http://dx.doi.org/10.3390/universe8100504.

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We highlight here the fact that the distantly observed luminosity of a spherically symmetric compact star radiating thermal radiation isotropically is higher by a factor of (1+zb)2 compared to the corresponding flat space-time case, where zb is the surface gravitational redshift of the compact star. In particular, we emphasize that if the thermal radiation is indeed emitted isotropically along the respective normal directions at each point, this factor of increment (1+zb)2 remains unchanged even if the compact object would lie within its photon sphere. Since a canonical neutron star has zb≈0.1, the actual X-ray luminosity from the neutron star surface could be ∼20% higher than what would be interpreted by ignoring the general relativistic effects described here. For a static compact object, supported by only isotropic pressure, compactness is limited by the Buchdahl limit zb<2.0. However, for compact objects supported by anisotropic pressure, zb could be even higher (zb<5.211). In addition, in principle, there could be ultra-compact objects having zb≫1. Accordingly, the general relativistic effects described here might be quite important for studies of thermal radiation from some ultra-compact objects.

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5

EKŞİ, Kazım Yavuz. "Neutron stars: compact objects with relativistic gravity." TURKISH JOURNAL OF PHYSICS 40 (2016): 127–38. http://dx.doi.org/10.3906/fiz-1510-11.

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6

CHATTOPADHYAY, PRADIP KUMAR, RUMI DEB, and BIKASH CHANDRA PAUL. "RELATIVISTIC SOLUTION FOR A CLASS OF STATIC COMPACT CHARGED STAR IN PSEUDO-SPHEROIDAL SPACETIME." International Journal of Modern Physics D 21, no. 08 (August 2012): 1250071. http://dx.doi.org/10.1142/s021827181250071x.

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Considering Vaidya–Tikekar metric, we obtain a class of solutions of the Einstein–Maxwell equations for a charged static fluid sphere. The physical 3-space (t = const. ) here is described by pseudo-spheroidal geometry. The relativistic solution for the theory is used to obtain models for charged compact objects; thereafter, a qualitative analysis of the physical aspects of compact objects are studied. The dependence of some of the properties of a superdense star on the parameters of the three geometry is explored. We note that the spheroidicity parameter a plays an important role for determining the properties of a compact object. A nonlinear equation of state (EOS) is required to describe a charged compact object with pseudo-spheroidal geometry, which we have shown for known masses of compact objects. We also note that the size of a static compact charged star is more than that of a static compact star without charge.

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Gallo, Emanuel, and Osvaldo M. Moreschi. "Modeling the dynamics of black holes through balanced equations of motion." International Journal of Geometric Methods in Modern Physics 16, no. 03 (March 2019): 1950034. http://dx.doi.org/10.1142/s0219887819500348.

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We present a general approach for the formulation of equations of motion for astrophysical compact objects in general relativistic theories. The objects are modeled as relativistic particles, which are assumed to be moving in a geometric background which in turn is asymptotically flat. The background can be affected by the compact object; so that our approach can be applied to binary systems; by concentrating on the main contributions coming from back reaction effects due to gravitational radiation. Our premises are different from the traditional post-Newtonian and self-force approaches since we make strong use of the asymptotic properties of the self geometry of the particle; as is described below. In particular, we use a center of mass setting, and relativistic individual dynamical times for each object. We expect our model to complement the other approaches in different regimes.

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Sharif, M., and Arfa Waseem. "Charged compact objects in f(R,T) gravity." International Journal of Modern Physics D 28, no. 02 (January 2019): 1950033. http://dx.doi.org/10.1142/s0218271819500330.

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This paper analyzes the effects of charge on the nature of relativistic compact star candidates with anisotropic distribution in the framework of [Formula: see text] gravity. For this purpose, we consider Krori–Barua solutions and obtain the values of unknown constants as well as charge using observational data of Her X-1, 4U1820-30 and SAX J 1808.4-3658 star models. For three viable [Formula: see text] models, we investigate the behavior of energy density, transverse as well as radial pressures in the interior geometry of these stars. The validity of energy conditions, effect of anisotropic factor and stability of these stellar models are also examined. We conclude that the effect of charge leads to more stable structures of relativistic compact objects.

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9

Chevalier, Roger A. "Compact Objects in Supernova Remnants." International Astronomical Union Colloquium 145 (1996): 399–406. http://dx.doi.org/10.1017/s0252921100008253.

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Core collapse in very massive stars can lead to a central black hole that swallows the rest of the star and in less massive stars to a central neutron star and explosion. There is probably an intermediate mass range that gives an explosion and a central black hole; supernova remnants with no observable central object are candidates. The association of pulsars with Type II supernovae gives an estimate of the pulsar power to be expected in a supernova, but the uncertainty in the initial pulsar periods gives a wide range in possible powers. The relativistic wind bubble model for the Crab Nebula has steadily developed and there are now predictions regarding particle acceleration in the optical wisps. The bubble model with expansion into supernova gas can also be applied to other young pulsar nebulae.

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10

Tomimatsu, Akira. "Relativistic Dynamos in Magnetospheres of Rotating Compact Objects." Astrophysical Journal 528, no. 2 (January 10, 2000): 972–78. http://dx.doi.org/10.1086/308190.

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11

DEB, RUMI, BIKASH CHANDRA PAUL, and RAMESH TIKEKAR. "Relativistic models of a class of compact objects." Pramana 79, no. 2 (July 24, 2012): 211–22. http://dx.doi.org/10.1007/s12043-012-0305-6.

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12

Pazameta, Zoran. "Maxwell-Proca Fields in Relativistic Astrophysical Compact Objects." Journal of Modern Physics 04, no. 08 (2013): 240–44. http://dx.doi.org/10.4236/jmp.2013.48a023.

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13

Nazar, H., M. Azam, G. Abbas, Riaz Ahmed, and R. Naeem. "Relativistic polytropic models of charged anisotropic compact objects." Chinese Physics C 47, no. 3 (March 1, 2023): 035109. http://dx.doi.org/10.1088/1674-1137/acae5b.

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Abstract In this paper, we introduce new viable solutions to the Einstein-Maxwell field equations by incorporating the features of anisotropic matter distributions within the realm of the general theory of relativity ( ). To obtain these solutions, we employed the Finch-Skea spacetime, along with a generalized polytropic equation of state ( ). We constructed various models of generalized polytropes by assuming different values of the polytropic index, i.e., , and . Next, numerous physical characteristics of these considered models were studied via graphical analysis, and they were found to obey all the essential conditions for astrophysical compact objects. Furthermore, such outcomes of charged anisotropic compact star models could be reproduced in various other cases including linear, quadratic, and polytropic

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14

Das, Shyam, Bikram Parida, Saibal Ray, and Shyamal Pal. "Role of Anisotropy on the Tidal Deformability of Compact Stellar Objects." Physical Sciences Forum 2, no. 1 (February 22, 2021): 29. http://dx.doi.org/10.3390/ecu2021-09311.

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In this paper, we introduce a framework to study the tidal deformation of relativistic anisotropic compact stars. Anisotropic stresses are ubiquitous in nature and widely used in modelling compact stellar objects. Tidal deformability of astrophysical compact objects is a natural effect of gravity, such as one produced by a companion in a binary system. In general relativity, the existence of this measurable effect of gravity can be quantified by their tidal Love numbers (TLN), which characterize the deformability of a neutron star (NS) from sphericity. The tidal deformability or polarizability parameter of an NS depends on its complex internal structure, and hence, the nature of the compact object can be studied by measuring the TLN. We choose a particular solution, which is the anisotropic generalization of the Tolman IV model, as the interior of the compact stellar object. The physical acceptability of the model has been shown graphically by considering the pulsar 4U 1608-52 with their current estimated mass and radius. By computing the quadrupole moment, we found that the TLN is dependent on anisotropy of the compact object. We graphically analyze the variation of the TLN against anisotropy for different compact objects with a compactness factor. The numerical value of TLN is given for different compact objects for physically acceptable values of the anisotropic parameter.

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Chakraborty, Koushik, Farook Rahaman, and Arkopriya Mallick. "A relativistic two-fluid model of compact stars." Modern Physics Letters A 32, no. 10 (March 27, 2017): 1750055. http://dx.doi.org/10.1142/s0217732317500559.

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We propose a relativistic model of compact star admitting conformal symmetry. Quark matter and baryonic matter which are considered as two different fluids, constitute the star. We define interaction equations between the normal baryonic matter and the quark matter and study the physical situations for repulsive, attractive and zero interaction between the constituent matters. The measured value of the Bag constant is used to explore the spacetime geometry inside the star. From the observed values of the masses of some compact objects, we have obtained theoretical values of the radii. Theoretical values of the radii match well with the previous predictions for such compact objects.

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16

Pandey, U. S. "General relativistic treatment of magnetofluid disk around compact objects." Astrophysics and Space Science 141, no. 2 (1988): 217–32. http://dx.doi.org/10.1007/bf00639490.

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17

Pandey, U. S. "General relativistic treatment of magnetofluid disk around compact objects." Astrophysics and Space Science 141, no. 2 (1988): 251–56. http://dx.doi.org/10.1007/bf00639492.

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18

FOSCHINI, LUIGI. "THE UNIFICATION OF RELATIVISTIC JETS." International Journal of Modern Physics: Conference Series 28 (January 2014): 1460188. http://dx.doi.org/10.1142/s2010194514601884.

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19

Becerra, L., H. Hernández, and L. A. Núñez. "Quasi-static thermal evolution of compact objects." Canadian Journal of Physics 93, no. 8 (August 2015): 920–34. http://dx.doi.org/10.1139/cjp-2014-0645.

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We study under what conditions the thermal peeling is present for dissipative local and quasi-local anisotropic spherical matter configurations. Thermal peeling occurs when different signs in the velocity of fluid elements appear, giving rise to the splitting of the matter configuration. The evolution is considered in the quasi-static approximation and the matter contents are radiant, anisotropic (unequal stresses) spherical local, and quasi-local fluids. The heat flux and the associated temperature profiles are described by causal thermodynamics consistent with this approximation. It is found that both types of configurations can exhibit thermal peeling when most of the radiated energy emerges from the first half of the distribution, and thermal peeling appears to be associated with extreme astrophysical scenarios (highly relativistic and very energetic gravitational system).

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20

KIM, Jinho. "Black Hole, Neutron Star and Numerical Relativity." Physics and High Technology 30, no. 6 (June 30, 2021): 7–13. http://dx.doi.org/10.3938/phit.30.017.

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Compact stars, e.g., black holes and neutron stars, are the most energetic objects in astrophysics. These objects are accompanied by extremely strong gravity and a high velocity, which approaches the speed of light. Therefore, compact objects should be dealt with in Einstein’s relativity. This article will briefly introduce a numerical method that will allow us to obtain general solutions in general relativity. Several applications using numerical relativistic simulations will also be presented.

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21

Mitra, Abhas. "Masses of radiation pressure supported stars in extreme relativistic realm." Proceedings of the International Astronomical Union 2, S238 (August 2006): 409–10. http://dx.doi.org/10.1017/s1743921307005698.

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AbstractWe discuss that in the extreme relativistic limit, i.e., when z ≫ 1, where z is the surface gravitational redshift, there could be radiation pressure supported and dominated stars with arbitrary gravitational mass, high or low. Such objects are called Eternally Collapsing Objects (ECOs). ECOs are practically as compact as Schwarzschild black holes (BH) and, observationally, are likely to be mistaken as BHs. Further since any object undergoing continued collapse must first become an ECO before becoming a true BH state characterized by M = 0, the observed BH Candidates are ECOs.

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22

Rojas C., W. A., and J. R. Arenas S. "Relativistic Origin of the Cutoff Parameter in Exotic Compact Objects." Gravitation and Cosmology 27, no. 2 (April 2021): 136–42. http://dx.doi.org/10.1134/s0202289321020122.

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23

Pazameta, Z. "A general relativistic model for magnetic monopole-infused compact objects." Astrophysics and Space Science 339, no. 2 (January 28, 2012): 317–22. http://dx.doi.org/10.1007/s10509-012-0996-7.

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24

Bonolis, Luisa. "Stellar structure and compact objects before 1940: Towards relativistic astrophysics." European Physical Journal H 42, no. 2 (April 28, 2017): 311–93. http://dx.doi.org/10.1140/epjh/e2017-80014-4.

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25

Mak, M. K., P. N. Dobson, and T. Harko. "Maximum mass-radius ratios for charged compact general relativistic objects." Europhysics Letters (EPL) 55, no. 3 (August 2001): 310–16. http://dx.doi.org/10.1209/epl/i2001-00416-x.

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26

MIGLIARI, SIMONE, GABRIELE GHISELLINI, JAMES MILLER-JONES, and DAVID RUSSELL. "JET MODELS FOR NEUTRON STAR X-RAY BINARIES." International Journal of Modern Physics: Conference Series 08 (January 2012): 108–13. http://dx.doi.org/10.1142/s2010194512004485.

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A variety of different models for jet formation have been developed over the years (mainly) for black hole systems and young stellar objects. Conclusive observational constraints which would favor one particular mechanism are difficult to obtain. Neutron star X-ray binaries are crucial for advancing our understanding of jet formation in general, building a bridge between the two most studied jet-producing classes of systems: black holes, i.e. non-magnetized, relativistic objects, and young stellar objects, i.e. non-relativistic, magnetized stars. I will briefly review the status of our observational knowledge of jets in neutron star X-ray binaries, with a focus on the parameters which might be involved in the production of jets. I will present recent works and current observational programs aiming to quantify the role of the compact object in the formation of jets in neutron star systems. Finally, I will test a jet model developed for young stellar objects, the X–wind model, on a neutron star system.

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27

Neslušan, L. "The second rise of general relativity in astrophysics." Modern Physics Letters A 34, no. 30 (September 28, 2019): 1950244. http://dx.doi.org/10.1142/s0217732319502444.

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The field equations, which are the mathematical basis of the theory of general relativity, provide us with a much larger variety of solutions to model the neutron stars and other compact objects than are used in the current astrophysics. We point out some important consequences of the new kind of solutions of the field equations, which can be obtained if the astrophysical usage of general relativity is not constrained, and outline an impact of these solutions on the models of internal structure of compact objects. If general relativity is not constrained, it enables to construct the stable object, with the outer surface above the event horizon, of whatever large mass. A new concept of relativistic compact object is a consequence of newly discovered property of gravity, yielded by the field equations in a spherically symmetric configuration of matter: in comparison with the Newtonian case, a particle is more effectively attracted by a nearer than a more distant matter.

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Ahmedov, Bobomurat. "Relativistic Astrophysics in Uzbekistan." Proceedings of the International Astronomical Union 13, S349 (December 2018): 276–82. http://dx.doi.org/10.1017/s1743921319000437.

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AbstractDuring the last twenty years, due to the extensive help and assistance of the international scientific community, there has been a great success in the development and establishment of new well-functioning and competitive scientific groups specialized in general relativity and relativistic astrophysics in Uzbekistan (Tashkent), Kazakhstan (Astana and Almaty), Kyrgyzstan (Bishkek) and great achievements have been made on the study in Central Asia in relativistic cosmology and astrophysics of compact gravitational objects.

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Rubiera-Garcia, Diego. "From fundamental physics to tests with compact objects in metric-affine theories of gravity." International Journal of Modern Physics D 29, no. 11 (May 26, 2020): 2041007. http://dx.doi.org/10.1142/s0218271820410072.

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This paper provides a short but comprehensible overview of some relevant aspects of metric-affine theories of gravity in relation to the physics and astrophysics of compact objects. We shall highlight the pertinence of this approach to supersede General Relativity on its strong-field regime, as well as its advantages and some of its difficulties. Moreover, we shall reflect on the present and future opportunities to test its predictions with relativistic and nonrelativistic stars, black holes, and other exotic horizonless compact objects.

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30

Martín, Eduardo L. "Evidence for Particle Acceleration and Nuclear Reactions around Compact Relativistic Objects." Annals of the New York Academy of Sciences 759, no. 1 (September 1995): 332–35. http://dx.doi.org/10.1111/j.1749-6632.1995.tb17557.x.

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31

Malaver, Manuel, and Rajan Iyer. "Some new relativistic charged models with anisotropic pressure." Physics & Astronomy International Journal 7, no. 4 (November 10, 2023): 240–49. http://dx.doi.org/10.15406/paij.2023.07.00315.

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In this paper, we found new classes of solutions to the Einstein-Maxwell field equations with matter anisotropic distribution incorporating a particular form of electric field intensity within the framework of general relativity. We use a metric potential or ansatz that depends on an adjustable parametern in order to get the new solutions. We generated new models of compact stars with n=1 and n=2. Graphical analysis allows us to conclude that the new models satisfy all the physical characteristics for astrophysical objects and can be very useful in the study and description of compact structures. We obtained models consistent with the pulsars PSR J1311-3430 and PSR J0952–0607.

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Jang, Uicheol, Hongsu Kim, and Yu Yi. "Thick Accretion Disk and Its Super Eddington Luminosity around a Spinning Black Hole." Journal of Astronomy and Space Sciences 38, no. 1 (March 2021): 39–44. http://dx.doi.org/10.5140/jass.2021.38.1.39.

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In the general accretion disk model theory, the accretion disk surrounding an astronomical object comprises fluid rings obeying Keplerian motion. However, we should consider relativistic and rotational effects as we close in toward the center of accretion disk surrounding spinning compact massive objects such as a black hole or a neutron star. In this study, we explore the geometry of the inner portion of the accretion disk in the context of Mukhopadhyay’s pseudo-Newtonian potential approximation for the full general relativity theory. We found that the shape of the accretion disk “puffs up” or becomes thicker and the luminosity of the disk could exceed the Eddington luminosity near the surface of the compact spinning black hole.

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Charles, P. A., A. D. Barnes, J. Casares, J. S. Clark, R. Cornelisse, C. Knigge, and D. Steeghs. "SS433 and the nature of ultra-luminous X-ray sources." Proceedings of the International Astronomical Union 2, S238 (August 2006): 219–24. http://dx.doi.org/10.1017/s1743921307005005.

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AbstractThe prototypical micro-quasar, SS433, one of the most bizarre objects in the Galaxy, is a weak X-ray source, yet the kinetic energy of its relativistic, precessing jets is vastly greater. In spite of its importance as the nearest example of directly observable relativistic phenomena, we know remarkably little about the nature of this binary system. There are ongoing arguments not only about the mass of the compact object, but even as to whether it is a black hole or a neutron star, an argument that recent high resolution optical spectroscopy has contributed to.Combined with the INTEGRAL discovery of a new class of highly obscured galactic high-mass X-ray binaries, one of which has been found to precess on a similar timescale to SS433, we suggest that these would indeed be seen by external observers as ULXs, once additional effects such as beaming (either relativistic or geometrical) are included.

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Bacchini, Fabio, Bart Ripperda, Alexander Y. Chen, and Lorenzo Sironi. "Numerical methods for General Relativistic particles." Proceedings of the International Astronomical Union 14, S342 (May 2018): 19–23. http://dx.doi.org/10.1017/s1743921318007834.

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AbstractWe present recent developments on numerical algorithms for computing photon and particle trajectories in the surrounding of compact objects. Strong gravity around neutron stars or black holes causes relativistic effects on the motion of massive particles and distorts light rays due to gravitational lensing. Efficient numerical methods are required for solving the equations of motion and compute i) the black hole shadow obtained by tracing light rays from the object to a distant observer, and ii) obtain information on the dynamics of the plasma at the microscopic scale. Here, we present generalized algorithms capable of simulating ensembles of photons or massive particles in any spacetime, with the option of including external forces. The coupling of these tools with GRMHD simulations is the key point for obtaining insight on the complex dynamics of accretion disks and jets and for comparing simulations with upcoming observational results from the Event Horizon Telescope.

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TSUPKO, OLEG YU. "MAGNETO-PLASMA PROCESSES IN RELATIVISTIC ASTROPHYSICS: MODERN DEVELOPMENTS." International Journal of Modern Physics D 22, no. 07 (June 2013): 1330016. http://dx.doi.org/10.1142/s0218271813300164.

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This contribution is a review of some talks presented at the session "Magneto-Plasma Processes in Relativistic Astrophysics" of the Thirteenth Marcel Grossmann Meeting MG13. We discuss the modern developments of relativistic astrophysics, connected with presence of plasma and magnetic fields. The influence of magneto-plasma processes on the structure of the compact objects and accretion processes is considered. We also discuss a crucial role of magnetic field for the mechanism of core-collapse supernova explosions. Gravitational lensing in plasma is also considered.

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Yusupova, R. М., G. R. Muchtarova, and R. N. Izmailov. "EDDINGTON LUMINOSITY LIMIT FOR MASSLESS WORMHOLES WITH SCALAR FIELD." Izvestia Ufimskogo Nauchnogo Tsentra RAN, no. 1 (March 28, 2022): 21–24. http://dx.doi.org/10.31040/2222-8349-2022-0-1-21-24.

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Most astrophysical objects growth by mass accretion. The almost universal presence of interstellar matter generally leads to the formation around compact objects of accretion disks. The emission of the radiation from the disk is determined by the external gravitational potentials of the central massive object, which in turn are essentially determined by its nature – neutron star, black hole, wormhole or naked singularity. Hence the astrophysical observations of the emission spectra from accretion disks may lead to the possibility of directly testing the physical and astrophysical properties of the compact general relativistic objects that have generated the disk via their gravitational field. The accretion process proceeds due to the viscosity caused by the turbulent motions of matter in the accretion disks. In turn, disks have an important property – luminosity, which today allows indirect observation of astrophysical compact objects. In this work, calculations are performed to determine the Eddington luminosity limit of an accretion disk formed around a massless wormhole. The dependence of the limiting luminosity in the throat region and at infinity on the dilatonic, electric and magnetic charges for the Goulart wormhole was established. An upper limit was also obtained for the dilatonic charge, at which the maximum value of Eddington's luminosity is reached. As a result, it was found that with an increase in the dilatonic charge, the value of the Eddington luminosity limit increases.

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Romero, Gustavo E. "Synergies in extragalactic and Galactic jet research." Proceedings of the International Astronomical Union 10, S313 (September 2014): 361–69. http://dx.doi.org/10.1017/s1743921315002495.

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AbstractThe discovery of relativistic jets and superluminal sources associated with accreting X-ray binaries in the Galaxy opened new ways of investigating the physics of outflows from compact objects. The short timescales and relatively large angular sizes of Galactic jets allow to probe the physics of relativistic outflows to unprecedented details. In this article I discuss results of recent modelling of Galactic jets, covering both radiative and dynamical aspects, which can shed light on different features of their extragalactic cousins.

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Böhmer, C. G., and T. Harko. "Bounds on the basic physical parameters for anisotropic compact general relativistic objects." Classical and Quantum Gravity 23, no. 22 (October 11, 2006): 6479–91. http://dx.doi.org/10.1088/0264-9381/23/22/023.

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Miller, J. M., A. D'Aì, M. W. Bautz, S. Bhattacharyya, D. N. Burrows, E. M. Cackett, A. C. Fabian, et al. "ON RELATIVISTIC DISK SPECTROSCOPY IN COMPACT OBJECTS WITH X-RAY CCD CAMERAS." Astrophysical Journal 724, no. 2 (November 12, 2010): 1441–55. http://dx.doi.org/10.1088/0004-637x/724/2/1441.

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40

Fraija, N., B. Betancourt Kamenetskaia, A. Galvan-Gamez, M. G. Dainotti, R. L. Becerra, S. Dichiara, P. Veres, and A. C. Caligula do E. S. Pedreira. "GRB Afterglow of the Sub-relativistic Materials with Energy Injection." Astrophysical Journal 933, no. 2 (July 1, 2022): 243. http://dx.doi.org/10.3847/1538-4357/ac714d.

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Abstract Sub-relativistic materials launched during the merger of binary compact objects and the core collapse of massive stars acquire velocity structures when expanding in a stratified environment. The remnant (either a spinning magnetized neutron star (NS) or a central black hole) from the compact object or core collapse could additionally inject energy into the afterglow via spin-down luminosity or/and by accreting fallback material, producing a refreshed shock, modifying the dynamics, and leading to rich radiation signatures at distinct timescales and energy bands with contrasting intensities. We derive the synchrotron light curves evolving in a stratified environment when a power-law velocity distribution parameterizes the energy of the shock, and the remnant continuously injects energy into the blast wave. As the most relevant case, we describe the latest multiwavelength afterglow observations (≳900 days) of the GW170817/GRB 170817A event via a synchrotron afterglow model with energy injection of a sub-relativistic material. The features of the remnant and the synchrotron emission of the sub-relativistic material are consistent with a spinning magnetized NS and the faster blue kilonova afterglow, respectively. Using the multiband observations of some short bursts with evidence of kilonovae, we provide constraints on the expected afterglow emission.

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Marcowith, A., G. Henri, and G. Pelletier. "A Study of Gamma Spectral Break in AGN." Symposium - International Astronomical Union 159 (1994): 347. http://dx.doi.org/10.1017/s0074180900175485.

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Since its launch, CGRO has detected more than 20 γ-ray emitting AGN, most of them associated with powerful, radio-loud, flat-spectrum objects, exhibiting VLBI superluminal motions. In the case of 3C279, the huge value of the apparent luminosity (∼ 1048erg.s−1) and the variability time-scale of a few days (Hartmann et al., 1992) gives a very large compacity lapp ≃ 200, that is, the medium should be completely thick to γ-rays. This contradiction can be explained if the γ-rays originate from a relativistic jet pointing at a small angle with respect to the line of sight (Maraschi et al., 1992). However, the still large value of compacity suggests the existence of an inner, more compact region where pair production can take place efficiently (Henri et al., 1993). This supports the so-called “two-flow” model, where the superluminal motion is attributed to the expansion of a relativistic pair plasma heated by a MHD jet from an accretion disk (Sol et al., 1989). Hence we propose to interpret the spectral break observed in many objects around a few MeV (Lichti et al., 1993) by an opacity effect due to photon-photon absorption by pair production.

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Falcke, H. "11.2. The nature of compact radio cores in galaxies." Symposium - International Astronomical Union 184 (1998): 459–60. http://dx.doi.org/10.1017/s0074180900085569.

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Compact radio cores, which are often assumed to mark the presence of a super-massive black hole, are not only found in the nuclei of powerful quasars but also in nearby galaxies. While in quasars they are typically associated with relativistic jets, the nature of those cores in low-luminosity AGN is less clear. Here, I will briefly mention some of the recent theories (ADAFs or jets) and observations of the latter class of objects.

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MAK, M. K., PETER N. DOBSON, and T. HARKO. "MAXIMUM MASS–RADIUS RATIO FOR COMPACT GENERAL RELATIVISTIC OBJECTS IN SCHWARZSCHILD–DE SITTER GEOMETRY." Modern Physics Letters A 15, no. 35 (November 20, 2000): 2153–58. http://dx.doi.org/10.1142/s0217732300002723.

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Upper limits for the mass–radius ratio are derived for arbitrary general relativistic matter distributions in the presence of a cosmological constant. General restrictions for the redshift and total energy (including the gravitational contribution) for compact objects in the Schwarzschild–de Sitter geometry are also obtained in terms of the cosmological constant and of the mean density of the star.

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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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Papavasileiou, Theodora, Odysseas Kosmas, and Ioannis Sinatkas. "Relativistic Magnetized Astrophysical Plasma Outflows in Black-Hole Microquasars." Symmetry 14, no. 3 (February 27, 2022): 485. http://dx.doi.org/10.3390/sym14030485.

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In this work, we deal with collimated outflows of magnetized astrophysical plasma known as astrophysical jets, which have been observed to emerge from a wide variety of astrophysical compact objects. The latter systems can be considered as either hydrodynamic (HD) or magnetohydrodynamic (MHD) in nature, which means that they are governed by non-linear partial differential equations. In some of these systems, the velocity of the jet is very high and they require relativistic MHD (RMHD) treatment. We mainly focus on the appropriate numerical solutions of the MHD (and/or RMHD) equations as well as the transfer equation inside the jet and simulate multi-messenger emissions from specific astrophysical compact objects. We use a steady state axisymmetric model assuming relativistic magnetohydrodynamic descriptions for the jets (astrophysical plasma outflows) and perform numerical simulations for neutrino, gamma-ray and secondary particle emissions. By adopting the existence of such jets in black hole microquasars (and also in AGNs), the spherical symmetry of emissions is no longer valid, i.e., it is broken, and the system needs to be studied accordingly. One of the main goals is to estimate particle collision rates and particle energy distributions inside the jet, from black-hole microquasars. As concrete examples, we choose the Galactic Cygnus X-1 and the extragalactic LMC X-1 systems.

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SAKAI, FUMIO, TERUNOBU NAKAJYO, TATSUYA YANAGIDA, and SHINJI ITO. "A COMPACT THOMSON X-RAY SOURCE AT SHI." International Journal of Modern Physics B 21, no. 03n04 (February 10, 2007): 465–72. http://dx.doi.org/10.1142/s0217979207042252.

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A compact, high-brightness x-ray source has been developed through Thomson scattering between photons and relativistic electrons. 33keV energy photons (maximum) were generated in a 165-degree interaction configuration with 38MeV electrons and 800nm-wavelength Ti :sapphire laser light. The number of total photons generated at an interaction point was 106 photons/pulse for a 0.8nC electron bunch charge and 150mJ laser pulse energy. In a 90-degree interaction configuration, 105 photons/pulse total photons were obtained (maximum). Transverse profiles of x-ray intensity and energy were measured by an x-ray CCD camera. These experiment profiles agreed with the analytical results. Imaging using this x-ray source was demonstrated as an application. X-ray images for some objects were taken with various lengths between the objects and the camera. As a result, the refraction contrast images were observed with 17keV x-rays.

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Gautschy, Alfred. "Any Recent Progress in the Theory of Pulsating Stars?" International Astronomical Union Colloquium 176 (2000): 324–33. http://dx.doi.org/10.1017/s0252921100058000.

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AbstractTo answer the topical question we survey synoptically the recent literature in pulsation theory. We restrict the topics to those which are not dealt with otherwise in this volume. We address research on roAp stars, EC 14026 variables, strange modes, luminous blue variables, pulsation-rotation coupling, and pulsations in compact objects seen from the classical, as well as the relativistic, viewpoint.

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Nouh, M. I., Y. A. Azzam, E. A.-B. Abdel-Salam, F. I. Elnagahy, and T. M. Kamel. "ANN AND ANALYTICAL SOLUTIONS TO RELATIVISTIC ISOTHERMAL GAS SPHERES." Revista Mexicana de Astronomía y Astrofísica 58, no. 2 (October 1, 2022): 321–32. http://dx.doi.org/10.22201/ia.01851101p.2022.58.02.13.

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Relativistic isothermal gas spheres are a powerful tool to model many astronomical objects, like compact stars and clusters of galaxies. In the present paper, we introduce an artificial neural network (ANN) algorithm and Taylor series to model the relativistic gas spheres using Tolman-Oppenheimer-Volkoff differential equations (TOV). Comparing the analytical solutions with the numerical ones revealed good agreement with maximum relative errors of 10−3. The ANN algorithm implements a three-layer feed-forward neural network built using a back-propagation learning technique that is based on the gradient descent rule. We analyzed the massradius relations and the density profiles of the relativistic isothermal gas spheres against different relativistic parameters and compared the ANN solutions with the analytical ones. The comparison between the two solutions reflects the efficiency of using the ANN to solve TOV equations.

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Frey, Sándor, Krisztina É. Gabányi, and Tao An. "The Quasar CTD 135 Is Not a Compact Symmetric Object." Symmetry 14, no. 2 (February 4, 2022): 321. http://dx.doi.org/10.3390/sym14020321.

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The radio-loud quasar CTD 135 (2234+282, J2236+2828) has been proposed as a candidate compact symmetric object (CSO), based on its symmetric radio structure revealed by multi-frequency very long baseline interferometry (VLBI) imaging observations on milliarcsec angular scales. CSOs are known as young jetted active galactic nuclei (AGN) whose relativistic plasma jets are misaligned with respect to the line of sight. The peculiarity of CTD 135 as a CSO candidate was its detection in γ-rays, while the vast majority of known γ-ray emitting AGN are blazars with jets pointing close to our viewing direction. Since only a handful of CSOs are known as γ-ray sources, the unambiguous identification of a single candidate is important for studying this rare class of objects. By collecting and interpreting observational data from the recent literature, we revisit the classification of CTD 135. We present evidence that the object, based on its flat-spectrum radio core with high brightness temperature, variability at multiple wavebands, and infrared colours should be classified as a blazar rather than a CSO.

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Romero, Gustavo E., and P. Sotomayor Checa. "Population III microquasars." International Journal of Modern Physics D 27, no. 10 (July 2018): 1844019. http://dx.doi.org/10.1142/s0218271818440194.

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We present the first results obtained in the elaboration of a complete model of a microquasar where the donor star is from Population III. These stars do not produce stellar winds so we consider that the mass loss is due exclusively to matter overflowing the Roche lobe towards the compact object, a maximally rotating black hole. The rate of accretion is extremely super-Eddington, with an intense mass loss from the system in the form of winds and jets. We calculate the relativistic particle content of the jet and the corresponding spectral energy distribution (SED) considering a lepto-hadronic model. Prospects for the cosmological implications of these objects are briefly discussed.

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