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Ayyesha K. Ahmed

Publications and source records attributed to Ayyesha K. Ahmed.

9 recordsLinked to original sources
arXiv2025

Spherical Accretion on a Schwarzschild-MOG Black Hole

In this paper we have examined spherical accretion onto Schwarzschild MOG Black Holes within the framework of Modified Gravity. Using isothermal test fluids, we analyze the behavior of the flow near the critical (sonic) point for various values of the equation of state parameter $k$. Depending on the fluid type, the flow exhibits either subsonic or supersonic behavior, with ultra-stiff and ultra-relativistic fluids allowing both regimes, while radiation and sub-relativistic fluids show more restricted dynamics. Phase space analysis helps visualize these transitions. We also compute the mass accretion rate and find that it increases with both radial distance and the MOG parameter $α$, highlighting the role of modified gravity in enhancing accretion processes around black holes

gr-qc↗
arXiv2025

Destroying the Kerr Newman MOG Black hole with Scalar Test Field

We test the weak cosmic censorship conjecture (WCCC) for the Kerr-Newman-modified gravity black hole (KN-MOG-BH) by interacting scalar test fields with the KN-MOG-BH. Neglecting backreaction effects, we first show that the scalar test fields with frequencies just above the superradiance threshold can overspin both extremal and nearly extremal KN-MOG-BHs, leading to the formation of naked singularities. Moreover, test fields can continuously push nearly extremal KN-MOG-BHs toward their extremal limit. Next, we incorporate backreaction effects, assuming that the event horizon's angular velocity rises prior to the test field's absorption. We show that backreaction prevents overspinning in the extremal KN-MOG-BH, whereas in the nearly extremal case, it fails to stop the BH from being overspun.

gr-qc↗
arXiv2022

Weak cosmic censorship conjecture for the (2+1)-dimensional charged BTZ black hole in the Einstein-Gauss-Bonnet Gravity

It is well known that ($2+1$) dimensional charged BTZ (Banados, Teitelboim, Zanelli) black hole can be overcharged by a charged scalar field and a charged particle in contrast to their analogues in ($3+1$) and higher dimensions. In this regard, it may play an important role to understand more deeply the properties of the ($2+1$)-dimensional charged black hole in the Einstein-Gauss-Bonnet (EGB) gravity. In this paper, we test the validity of the weak cosmic censorship conjecture for the ($2+1$)-dimensional charged black hole in novel EGB theory derived recently by Henniger et. al (2021). We show that the minimum energy that particle can have at the horizon becomes negative for both an extremal and nearly-extremal BTZ black holes in EGB gravity. It is proven that both extremal and nearly-extremal $(2+1)$ dimensional BTZ black hole could be overcharged in EGB theory, leading to the violation of the weak cosmic censorship conjecture (WCCC), which is in good agreement with the results obtained for the classical BTZ black hole.

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arXiv2020

Accretion on High Derivative Asymptotically Safe Black Holes

Asymptotically safe gravity is one effective approach to quantum gravity. It is important to differentiate the modified gravity inspired by asymptotically safe gravity. In this paper, we examine the matter particles dynamics near the improved version of Schwarzschild black hole. We assume that in the context of asymptotically safe gravity scenario the ambient matter surrounding the black hole is of isothermal in nature and investigate the spherical accretion of matter by deriving solutions at critical points. The analysis for the various values of the state parameter for isothermal test fluids, viz., $k=1,~1/2,~1/3,~1/4$ show the possibility of accretion onto asymptotically safe black hole. We formulate the accretion problem as Hamiltonian dynamical system and explain its phase flow in detail which reveals interesting results in asymptotically safe gravity theory.

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arXiv2018

Spherical accretion by normal and phantom Einstein--Maxwell--dilaton black holes

We investigate the spherical accretion process for general static spherically symmetric fluids. We analyze this process by using the general metric ansatz for spherically symmetric black holes. We specialize to the case of normal and phantom isothermal fluids and investigate their accretion process onto normal and phantom Einstein-Maxwell-dilaton black holes. Backreaction effects are discussed.

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arXiv2016

Accretion on Reissner-Nordstrom-(anti)-de Sitter Black Hole with Global Monopole

In this paper, we investigate the accretion on the Reissner-Nordström anti-de-Sitter black hole with global monopole charge. We discuss the general solutions of accretion using the isothermal and polytropic equations of state for steady state, spherically symmetric, non-rotating accretion on the black hole. In the case of isothermal flow, we consider some specific fluids and derive their solutions at the sonic point as well. However, in case of polytropic fluid we calculate the general expressions only, as there exists no global (Bondi) solutions for polytropic test fluids. In addition to this, the effect of fluid on the mass accretion rate are also studied. Moreover, the large monopole parameter $β$ greatly suppresses the maximum accretion rate.

gr-qc↗
arXiv2016

Cyclic and heteroclinic flows near general static spherically symmetric black holes

We investigate the Michel-type accretion onto a static spherically symmetric black hole. Using a Hamiltonian dynamical approach, we show that the standard method employed for tackling the accretion problem has masked some properties of the fluid flow. We determine new analytical solutions that are neither transonic nor supersonic as the fluid approaches the horizon(s); rather, they remain subsonic for all values of the radial coordinate. Moreover, the three velocity vanishes and the pressure diverges on the horizon(s), resulting in a flowout of the fluid under the effect of its own pressure. This is in favor of an earlier prediction that pressure-dominant regions form near the horizon. This result does not depend on the form of the metric and it applies to a neighborhood of any horizon where the time coordinate is timelike. For anti-de Sitter-like $\text{f}(R)$ black holes we discuss the stability of the critical flow and determine separatrix heteroclinic orbits. For de Sitter-like $\text{f}(R)$ black holes, we construct polytropic cyclic, non-homoclinic, physical flows connecting the two horizons. These flows become non-relativistic for Hamiltonian values higher than the critical value allowing for a good estimate of the proper period of the flow.

gr-qc↗
arXiv2016

Astrophysical flows near $f(T)$ gravity black holes

In this paper, we study the accretion process for fluids flowing near a black hole in the context of $f(T)$ teleparallel gravity. Specifically, by performing a dynamical analysis by a Hamiltonian system, we are able to find the sonic points. After that, we consider different isothermal test fluids in order to study the accretion process when they are falling onto the black hole. We found that these flows can be classified according to the equation of state and the black hole features. Results are compared in $f(T)$ and $f(R)$ gravity.

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