Advanced search    

Search: authors:"Cosimo Bambi"

21 papers found.
Use AND, OR, NOT, +word, -word, "long phrase", (parentheses) to fine-tune your search.

Scalar perturbations and quasi-normal modes of a nonlinear magnetic-charged black hole surrounded by quintessence

We study scalar perturbations and quasi-normal modes of a nonlinear magnetic-charged black hole surrounded by quintessence. The time evolution of scalar perturbations is studied for different parameters associated with the black hole solution. We also study the reflection and transmission coefficients along with absorption cross section for the considered black hole spacetime. It...

Gravitational lensing for a boosted Kerr black hole in the presence of plasma

We obtain the deflection angle for a boosted Kerr black hole in the weak field approximation. We also study the behavior of light in the presence of plasma by considering different distributions: singular isothermal sphere, non-singular isothermal gas sphere, and plasma in a galaxy cluster. We find that the dragging of the inertial system along with the boosted parameter...

A general study of regular and singular black hole solutions in Einstein’s conformal gravity

( 6 ), 1741 ( 2014 ) 10. R.Jonas Mureika, Gabriele U. Varieschi., Black hole shadows in fourth-order conformal weyl gravity . Can. J. Phys . 95 ( 12 ), 1299 - 1306 ( 2017 ) 11. Cosimo Bambi , Leonardo ... Modesto, Les?aw Rachwa?, Spacetime completeness of non-singular black holes in conformal gravity . J. Cosmol. Astropart. Phys . 2017 ( 05 ), 003 ( 2017 ) 12. Cosimo Bambi , Black Holes: A Laboratory for

Iron line spectroscopy of black holes in asymptotically safe gravity

We study the iron line shape expected in the reflection spectrum of accretion disks around black holes in asymptotically safe gravity. We compare the results of our simulations with the iron line shapes expected in the reflection spectrum of accretion disks around Kerr black holes to see if the technique of iron line spectroscopy can be used as a tool to test asymptotically safe...

Formation and evaporation of an electrically charged black hole in conformal gravity

Extending previous work on the formation and the evaporation of black holes in conformal gravity, in the present paper we study the gravitational collapse of a spherically symmetric and electrically charged thin shell of radiation. The process creates a singularity-free black hole. Assuming that in the evaporation process the charge Q is constant, the final product of the...

Observational properties of rigidly rotating dust configurations

We study the observational properties of a class of exact solutions of Einstein’s field equations describing stationary, axially symmetric, rigidly rotating dust (i.e. non-interacting particles). We ask the question whether such solutions can describe astrophysical rotating dark matter clouds near the center of galaxies and we probe the possibility that they may constitute an...

Energy conditions of non-singular black hole spacetimes in conformal gravity

Conformal gravity can elegantly solve the problem of spacetime singularities present in Einstein’s gravity. For every physical spacetime, there is an infinite family of conformally equivalent singularity-free metrics. In the unbroken phase, every non-singular metric is equivalent and can be used to infer the physical properties of the spacetime. In the broken phase, a Higgs-like...

Blandford–Znajek mechanism in black holes in alternative theories of gravity

According to the Blandford–Znajek mechanism, black hole jets are powered by the rotational energy of the compact object. In this work, we consider the possibility that the metric around black holes may not be described by the Kerr solution and we study how this changes the Blandford–Znajek model. If the Blandford–Znajek mechanism is responsible for the formation of jets, the...

Note on a new parametrization for testing the Kerr metric

We propose a new parametrization for testing the Kerr nature of astrophysical black hole candidates. The common approaches focus on the attempt to constrain possible deviations from the Kerr solution described by new terms in the metric. Here we adopt a different perspective. The mass and the spin of a black hole make the spacetime curved and we want to check whether they do it...

Black supernovae and black holes in non-local gravity

In a previous paper, we studied the interior solution of a collapsing body in a non-local theory of gravity super-renormalizable at the quantum level. We found that the classical singularity is replaced by a bounce, after which the body starts expanding. A black hole, strictly speaking, never forms. The gravitational collapse does not create an event horizon but only an apparent...

Scattering of particles by deformed non-rotating black holes

We study the excitation of axial quasi-normal modes of deformed non-rotating black holes by test particles and we compare the associated gravitational wave signal with that expected in general relativity from a Schwarzschild black hole. Deviations from standard predictions are quantified by an effective deformation parameter, which takes into account deviations from both the...

Testing the nature of the black hole candidate in GRO J1655-40 with the relativistic precession model

Quasi-periodic oscillations (QPOs) are a common feature in the X-ray flux of stellar-mass black hole candidates, but their exact origin is not yet known. Recently, some authors have pointed out that data of GRO J1655-40 simultaneously show three QPOs that nicely fit in the relativistic precession model. However, they find an estimate of the spin parameter that disagrees with the...

Attempt to explain black hole spin in X-ray binaries by new physics

Cosimo Bambi 0 0 Department of Physics, Center for Field Theory and Particle Physics, Fudan University , Shanghai 200433 , China It is widely believed that the spin of black holes in X-ray binaries

Shadows of CPR black holes and tests of the Kerr metric

We study the shadow of the Cardoso–Pani–Rico black hole for different values of the black hole spin \(a_*\), the deformation parameters \(\epsilon _3^t\) and \(\epsilon _3^r\), and the viewing angle i. We find that the main impact of the deformation parameter \(\epsilon _3^t\) is the change of the size of the shadow, while the deformation parameter \(\epsilon _3^r\) affects the...

X-ray spectropolarimetric measurements of the Kerr metric

It is thought that the spacetime geometry around black hole candidates is described by the Kerr solution, but an observational confirmation is still missing. Today, the continuum-fitting method and the analysis of the iron K\(\alpha \) line cannot unambiguously test the Kerr paradigm because of the degeneracy among the parameters of the system, in the sense that it is impossible...

A Note on the Observational Evidence for the Existence of Event Horizons in Astrophysical Black Hole Candidates

Elewyck Copyright © 2013 Cosimo Bambi. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any

Can static regular black holes form from gravitational collapse?

Starting from the Oppenheimer–Snyder model, we know how in classical general relativity the gravitational collapse of matter forms a black hole with a central spacetime singularity. It is widely believed that the singularity must be removed by quantum-gravity effects. Some static quantum-inspired singularity-free black hole solutions have been proposed in the literature, but when...

Can we observationally test the weak cosmic censorship conjecture?

Lingyao Kong 0 Daniele Malafarina 0 Cosimo Bambi 0 0 Department of Physics, Center for Field Theory and Particle Physics, Fudan University , 220 Handan Road, Shanghai 200433, China In general

Terminating black holes in asymptotically free quantum gravity

Cosimo Bambi 0 Daniele Malafarina 0 Leonardo Modesto 0 0 Department of Physics, Center for Field Theory and Particle Physics, Fudan University , Shanghai 200433, China We study the homogeneous