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M Sharif - One of the best experts on this subject based on the ideXlab platform.
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effects of charge on Dynamical Instability of spherical collapse in f r t gravity
General Relativity and Gravitation, 2018Co-Authors: M Sharif, Arfa WaseemAbstract:The effects of charge on stable structure of spherically symmetric collapsing model comprising anisotropic matter distribution are studied in f(R, T) gravity, where R and T correspond to scalar curvature and trace of the energy-momentum tensor, respectively. We construct the field equations, Maxwell equations and Dynamical equations in this scenario. We employ linear perturbation scheme on physical variables, metric functions as well as modified terms to establish the evolution or collapse equation for a consistent functional form of f(R, T) gravity. We investigate the limit of Instability in Newtonian as well as post Newtonian regimes. It is found that charge plays a fundamental role to slow down the collapse and form a more stable system.
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Dynamical Instability of gaseous sphere in the reissner nordstrom limit
General Relativity and Gravitation, 2016Co-Authors: M Sharif, Saadia MumtazAbstract:In this paper, we study the Dynamical Instability of gaseous sphere under radial oscillations approaching the Reissner–Nordstrom limit. For this purpose, we derive linearized perturbed equation of motion following the Eulerian and Lagrangian approaches. We formulate perturbed pressure in terms of adiabatic index by employing the conservation of baryon numbers. A variational principle is established to evaluate characteristic frequencies of oscillations which lead to the criteria for Dynamical stability. The Dynamical Instability of homogeneous sphere as well as relativistic polytropes with different values of charge in Newtonian and post-Newtonian regimes is explored. We also find their radii of Instability in terms of the Reissner–Nordstorm radius. We conclude that Dynamical Instability occurs if the gaseous sphere contracts to the Reissner–Nordstorm radius for different values of charge.
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Dynamical Instability of spherical collapse in f t gravity
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: M Sharif, Shamaila RaniAbstract:We study the Dynamical Instability of a spherically symmetric collapsing star in the context of f (T) gravity. For this purpose, we assume power-law f (T) model with non-dissipative anisotropic fluid distribution and find the Dynamical equations which are used to construct collapse equation. The perturbation scheme is applied to all matter, metric and f (T) functions. We formulate the collapse equation under perturbation to investigate Dynamical Instability ranges in Newtonian as well as post-Newtonian regimes. It is found that these ranges depend on structural quantities of the collapsing star through adiabatic index. Finally, we develop some constraints on positivity of these quantities to meet the Dynamical Instability condition.
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electromagnetic field and Dynamical Instability of collapse with cdtt model
Astroparticle Physics, 2014Co-Authors: M Sharif, Z YousafAbstract:Abstract This work investigates the Dynamical Instability of the relativistic self-gravitating collapsing fluids with electromagnetic field in Carrol–Duvvuri–Trodden–Turner (CDTT) f ( R ) model for spherical symmetric spacetime. In this scenario, we provide Dynamical equations from the contracted Bianchi identities for the usual, effective dark source and electromagnetic energy–momentum tensor. The perturbation technique is used on the metric variables which ultimately induce perturbation on the selected f ( R ) model and on the physical variables. We conclude that higher curvature terms of CDTT model, density profile, electromagnetism and pressure anisotropy affect the range of Instability at the Newtonian and post Newtonian regimes. It is worthwhile to mention here that our results approach asymptotically to general relativity solutions when δ → 0 .
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effects of electromagnetic field on the Dynamical Instability of expansionfree gravitational collapse
arXiv: General Relativity and Quantum Cosmology, 2013Co-Authors: M Sharif, M AzamAbstract:In this paper, we discuss the effects of electromagnetic field on the Dynamical Instability of a spherically symmetric expansionfree gravitational collapse. Darmois junction conditions are formulated by matching interior spherically symmetric spacetime to exterior Reissner-Nordstr$\ddot{o}$m spacetime. We investigate the role of different terms in the Dynamical equation at Newtonian and post Newtonian regimes by using perturbation scheme. It is concluded that Instability range depends upon pressure anisotropy, radial profile of energy density and electromagnetic field, but not on the adiabatic index $\Gamma$. In particular, the electromagnetic field reduces the unstable region.
Konstantin Batygin - One of the best experts on this subject based on the ideXlab platform.
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pre late heavy bombardment evolution of the earth s obliquity
The Astrophysical Journal, 2014Co-Authors: Konstantin BatyginAbstract:The Earth's obliquity is stabilized by the Moon, which facilitates a rapid precession of the Earth's spin axis, detuning the system away from resonance with orbital modulation. It is, however, likely that the architecture of the solar system underwent a Dynamical Instability-driven transformation, where the primordial configuration was more compact. Hence, the characteristic frequencies associated with orbital perturbations were likely faster in the past, potentially allowing for secular resonant encounters. In this work, we examine if, at any point in the Earth's evolutionary history, the obliquity varied significantly. Our calculations suggest that even though the orbital perturbations were different, the system nevertheless avoided resonant encounters throughout its evolution. This indicates that the Earth obtained its current obliquity during the formation of the Moon.
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formation and evolution of planetary systems in presence of highly inclined stellar perturbers
Astronomy and Astrophysics, 2011Co-Authors: Konstantin Batygin, Alessandro Morbidelli, K TsiganisAbstract:Context. The presence of highly eccentric extrasolar planets in binary stellar systems suggests that the Kozai effect has played an important role in shaping their Dynamical architectures. However, the formation of planets in inclined binary systems poses a considerable theoretical challenge, as orbital excitation due to the Kozai resonance implies destructive, high-velocity collisions among planetesimals. Aims. To resolve the apparent difficulties posed by Kozai resonance, we seek to identify the primary physical processes responsible for inhibiting the action of Kozai cycles in protoplanetary disks. Subsequently, we seek to understand how newly-formed planetary systems transition to their observed, Kozai-dominated Dynamical states. Methods. The main focus of this study is on understanding the important mechanisms at play. Thus, we rely primarily on analytical perturbation theory in our calculations. Where the analytical approach fails to suffice, we perform numerical N-body experiments. Results. We find that theoretical difficulties in planet formation arising from the presence of a distant (a ~ 1000 AU) companion star, posed by the Kozai effect and other secular perturbations, can be overcome by a proper account of gravitational interactions within the protoplanetary disk. In particular, fast apsidal recession induced by disk self-gravity tends to erase the Kozai effect, and ensure that the disk’s unwarped, rigid structure is maintained. Subsequently, once a planetary system has formed, the Kozai effect can continue to be wiped out as a result of apsidal precession, arising from planet-planet interactions. However, if such a system undergoes a Dynamical Instability, its architecture may change in such a way that the Kozai effect becomes operative. Conclusions. The results presented here suggest that planetary formation in highly inclined binary systems is not stalled by perturbations, arising from the stellar companion. Consequently, planet formation in binary stars is probably no different from that around single stars on a qualitative level. Furthermore, it is likely that systems where the Kozai effect operates, underwent a transient phase of Dynamical Instability in the past.
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formation and evolution of planetary systems in presence of highly inclined stellar perturbers
arXiv: Earth and Planetary Astrophysics, 2011Co-Authors: Konstantin Batygin, Alessandro Morbidelli, K TsiganisAbstract:The presence of highly eccentric extrasolar planets in binary stellar systems suggests that the Kozai effect has played an important role in shaping their Dynamical architectures. However, the formation of planets in inclined binary systems poses a considerable theoretical challenge, as orbital excitation due to the Kozai resonance implies destructive, high-velocity collisions among planetesimals. To resolve the apparent difficulties posed by Kozai resonance, we seek to identify the primary physical processes responsible for inhibiting the action of Kozai cycles in protoplanetary disks. Subsequently, we seek to understand how newly-formed planetary systems transition to their observed, Kozai-dominated Dynamical states. We find that theoretical difficulties in planet formation arising from the presence of a distant companion star, posed by the Kozai effect and other secular perturbations, can be overcome by a proper account of gravitational interactions within the protoplanetary disk. In particular, fast apsidal recession induced by disk self-gravity tends to erase the Kozai effect, and ensure that the disk's unwarped, rigid structure is maintained. Subsequently, once a planetary system has formed, the Kozai effect can continue to be wiped out as a result of apsidal precession, arising from planet-planet interactions. However, if such a system undergoes a Dynamical Instability, its architecture may change in such a way that the Kozai effect becomes operative. The results presented here suggest that planetary formation in highly inclined binary systems is not stalled by perturbations, arising from the stellar companion. Consequently, planet formation in binary stars is probably no different from that around single stars on a qualitative level. Furthermore, it is likely that systems where the Kozai effect operates, underwent a transient phase of Dynamical Instability in the past.
M Zubair - One of the best experts on this subject based on the ideXlab platform.
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shear free condition and Dynamical Instability in f r t gravity
European Physical Journal C, 2015Co-Authors: Ifra Noureen, M Zubair, A A Bhatti, G AbbasAbstract:The implications of the shear-free condition on the Instability range of an anisotropic fluid in f(R, T) are studied in this manuscript. A viable f(R, T) model is chosen to arrive at stability criterion, where R is Ricci scalar and T is the trace of energy-momentum tensor. The evolution of a spherical star is explored by employing a perturbation scheme on the modified field equations and contracted Bianchi identities in f(R, T). The effect of the imposed shear-free condition on the collapse equation and adiabatic index $$\Gamma $$ is studied in the Newtonian and post-Newtonian regimes.
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on Dynamical Instability of spherical star in f r t gravity
Astrophysics and Space Science, 2015Co-Authors: Ifra Noureen, M ZubairAbstract:This work is based on stability analysis of spherically symmetric collapsing star surrounding in locally anisotropic environment in f(R,T) gravity, where R is Ricci scalar and T corresponds to the trace of energy momentum tensor. Field equations and Dynamical equations are presented in the context of f(R,T) gravity. Perturbation scheme is employed on Dynamical equations to find the collapse equation. Furthermore, condition on adiabatic index Γ is constructed for Newtonian and post-Newtonian eras to address Instability problem. Some constraints on physical quantities are imposed to maintain stable stellar configuration. The results in this work are in accordance with f(R) gravity for specific case.
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Dynamical Instability and expansion free condition in f r t gravity
European Physical Journal C, 2015Co-Authors: Ifra Noureen, M ZubairAbstract:A Dynamical analysis of a spherically symmetric collapsing star surrounded by a locally anisotropic environment under an expansion-free condition is presented in \(f(R,T)\) gravity, where \(R\) corresponds to the Ricci scalar and \(T\) stands for the trace of the energy momentum tensor. The modified field equations and evolution equations are reconstructed in the framework of \(f(R,T)\) gravity. In order to acquire the collapse equation we implement the perturbation on all matter variables and dark source components comprising the viable \(f(R,T)\) model. The Instability range is described in the Newtonian and post-Newtonian approximation. It is observed that the unequal stresses and density profile define the Instability range rather than the adiabatic index. However, the physical quantities are constrained to maintain positivity of the energy density and a stable stellar configuration.
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Dynamical Instability and expansion free condition in f r t gravity
arXiv: General Relativity and Quantum Cosmology, 2015Co-Authors: Ifra Noureen, M ZubairAbstract:Dynamical analysis of spherically symmetric collapsing star surrounding in locally anisotropic environment with expansion-free condition is presented in $f(R,T)$ gravity, where $R$ corresponds to Ricci scalar and $T$ stands for the trace of energy momentum tensor. The modified field equations and evolution equations are reconstructed in the framework of $f(R,T)$ gravty. In order to acquire the collapse equation we implement the perturbation on all matter variables and dark source components comprising the viable $f(R,T)$ model. The Instability range is described in Newtonian and post-Newtonian eras by constraining the adiabatic index $\Gamma$ to maintain viability of considered model and stable stellar configuration.
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Dynamical Instability of spherical star in f r t gravity
arXiv: General Physics, 2014Co-Authors: Ifra Noureen, M ZubairAbstract:This work is based on stability analysis of spherically symmetric collapsing star surrounding in locally anisotropic environment in $f(R,T)$ gravity, where $R$ is Ricci scalar and $T$ corresponds to the trace of energy momentum tensor. Field equations and Dynamical equations are presented in the context of $f(R,T)$ gravity. Perturbation schem is employed on Dynamical equations to find the collapse equation. Furthermore, condition on adiabatic index $\Gamma$ is constructed for Newtonian and post-Newtonian eras to address Instability problem. Some constraints on physical quantities are imposed to maintain stable stellar configuration. The results in this work are in accordance with $f(R)$ gravity for specific case.
Massimo Inguscio - One of the best experts on this subject based on the ideXlab platform.
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observation of Dynamical Instability for a bose einstein condensate in a moving 1d optical lattice
Physical Review Letters, 2004Co-Authors: L Fallani, C. Fort, L De Sarlo, M Modugno, Robert Saers, Massimo InguscioAbstract:Observation of Dynamical Instability for a Bose-Einstein Condensate in a Moving 1D Optical Lattice
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observation of Dynamical Instability for a bose einstein condensate in a moving 1d optical lattice
Physical Review Letters, 2004Co-Authors: L Fallani, C. Fort, L De Sarlo, M Modugno, Robert Saers, J E Lye, Massimo InguscioAbstract:We have experimentally studied the unstable dynamics of a harmonically trapped Bose-Einstein condensate loaded into a 1D moving optical lattice. The lifetime of the condensate in such a potential exhibits a dramatic dependence on the quasimomentum state. This is unambiguously attributed to the onset of Dynamical Instability, after a comparison with the predictions of the Gross-Pitaevskii theory. Deeply in the unstable region we observe the rapid appearance of complex structures in the atomic density profile, as a consequence of the condensate phase uniformity breakdown.
Simon F Ross - One of the best experts on this subject based on the ideXlab platform.
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Smeared D0 charge and the Gubser-Mitra conjecture
Classical and Quantum Gravity, 2005Co-Authors: Simon F Ross, Toby WisemanAbstract:We relate a Dp or NS-brane with D0-brane charge smeared over its worldvolume to the system with no D0-charge. This allows us to generalise Reall's partial proof of the Gubser-Mitra conjecture. We show explicitly for specific examples that the Dynamical Instability coincides with thermodynamic Instability in the ensemble where the D0-brane charge can vary. We also comment on consistency checks of the conjecture for more complicated systems, using the example of the D4 with F1 and D0 charges smeared on its worldvolume.
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smeared branes and the gubser mitra conjecture
Physical Review D, 2004Co-Authors: Paul Bostock, Simon F RossAbstract:We argue that smeared brane solutions, where a charged black p-brane is smeared uniformly over one of the transverse directions, can have a Gregory-Laflamme-type Dynamical Instability in the smeared direction even when the solution is locally thermoDynamically stable. These thus seem to provide counterexamples to the Gubser-Mitra conjecture, which links local Dynamical and thermodynamic stability. By exploiting an ansatz due to Harmark and Obers, which relates charged solutions to neutral ones, we demonstrate the existence of a threshold unstable mode. This provides strong evidence for the existence of a Dynamical Instability, although we do not demonstrate its existence directly.
