Related papers: Super-spinning compact objects generated by thick …
We provide a description of a thin accretion disc for a static spherically symmetric black holes in $f(R)$ gravity. In this regard, we first study the horizons of black holes in $f(R)$ gravity. The equation of motion and effective potential…
We investigate the properties of the most distant quasars ULASJ134208.10+092838.61 ($z = 7.54$), ULASJ112001.48+064124.3 ($z = 7.08$) and DELSJ003836.10-152723.6 ($z = 7.02$) studying their Optical-UV emission that shows clear evidence of…
Estimations of black hole spin in the three Galactic microquasars GRS 1915+105, GRO J1655-40, and XTE J1550-564 have been carried out based on spectral and timing X-ray measurements and various theoretical concepts. Among others, a…
In many black hole systems, the accretion disk is expected to be misaligned with respect to the black hole spin axis. If the scale height of the disk is much smaller than the misalignment angle, the spin of the black hole can tear the disk…
The detection of fast quasi-periodic variability from accreting black holes and neutron stars has been used to constrain their masses, radii, and spins. If the observed oscillations are linear modes in the accretion disks, then bounds can…
Einstein's theory of general relativity has been extensively tested in weak gravitational fields, mainly with experiments in the Solar System and observations of radio pulsars, and current data agree well with the theoretical predictions.…
In general relativity, astrophysical black holes are uniquely described by the Kerr metric. Observational tests of the Kerr nature of these compact objects and, hence, of general relativity, require a metric that encompasses a broader class…
The radiative efficiencies ($\eta$) of 72 luminous unobscured Active Galactic Nuclei (AGNs) at $z\sim1.5-3.5$, powered by some of the most massive black holes (BHs), are constrained. The analysis is based on accretion disk (AD) models,…
We present a general relativistic accretion disc model and its application to the soft-state X-ray spectra of black hole binaries. The model assumes a flat, optically thick disc around a rotating Kerr black hole. The disc locally radiates…
X-ray reflection spectroscopy is a powerful tool for probing the strong gravity region of black holes and can be used for testing general relativity in the strong field regime. Simplifications of the available relativistic reflection models…
One of the primary means of determining the spin of an astrophysical black hole is by actually measuring the inner radius of a surrounding accretion disk and using that to infer the spin. By comparing a number of different estimates of the…
In Sgr A* at the Galactic center, by far the closest and easiest supermassive black hole we can study, the observational evidence is increasingly pointing to the presence of a compact, hot, magnetized disk feeding the accretor. In such…
We prescribe a method to study the effects of self-gravity of accretion disk around a black hole associated with long Gamma Ray Bursts (GRBs) in an evolving background Kerr metric. This is an extension to our previous work where we…
We study the gravitational collapse and formation of the Kerr black hole from the rotating progenitor star. We follow the evolution of black hole spin, coupled with its increasing mass. We study the effect of different level of rotation…
We present results from fully general relativistic three-dimensional numerical studies of thick-disk accretion onto a rapidly-rotating (Kerr) black hole with a spin axis that is tilted (not aligned) with the angular momentum vector of the…
We have studied the accreting black hole binary GX 339--4 using two highly accurate broad-band X-ray data sets in very soft spectral states from simultaneous NICER and NuSTAR observations. Joint fitting of both data sets with relativistic…
It has been suggested that amplitudes for quantum higher-spin massive particles exchanging gravitons lead, via a classical limit, to results for scattering of spinning black holes in general relativity, when the massive particles are in a…
We investigate a family of spherically symmetric, static, charged regular black hole solutions derived within the framework of Einstein-nonlinear electrodynamics. Our study focuses on examining the characteristics of accretion disks in the…
The soft excess seen in many AGN is most probably due to partially ionized material moving at relativistic speeds close to the black hole. There are currently two potential geometries for this material, one where it is out of the line of…
In the standard paradigm, astrophysical black holes can be described solely by their mass and angular momentum - commonly referred to as `spin' - resulting from the process of their birth and subsequent growth via accretion. Whilst the mass…