We analyze the properties of the Kerr black hole (BH) photon shell, focusing on the influence of aggregates of corotating and counterrotating toroids (ringed accretion disks - RAD) orbiting in the BH photon shell. The particular case of a corotating accretion disk orbiting in the BH ergoregion is also investigated. We study influence on the BH shadow boundary, fixing the conditions under which...
Relativistic jets observed in active galactic nuclei and produced by supermassive black holes are highly sensitive to the structure and dynamics of their surrounding magnetic fields. In this talk, I will argue that these magnetospheres are shaped not only by internally generated magnetic fields - such as those from the accretion disk, as typically theorized - but also by external fields....
We investigate various electromagnetic field configurations
around a rotating Kerr black hole, plotting the electric and magnetic
vector fields for different observers. The study employs a black hole
magnetosphere model that combines an external uniform magnetic field
with an internal split magnetic monopole configuration. Additionally,
we aim to address the Meissner effect,...
An extended test body in Newtonian gravity usually deviates from its corresponding point-particle motion: its center-of-masss trajectory is affected by its own internal structure, generating quite diverse phenomena. Here we consider small test bodies with symmetries such that their spin are identically zero along their orbits, and work in the quadrupole approximation. We show that in this...
We explore the dynamics of magnetized test particles in the Schwarzschild spacetime under the influence of a large-scale magnetic field. This work is well-motivated astrophysically by the dynamics of magnetized inhomogeneities in accretion flows around compact objects such as black holes or neutron stars. It could also be motivated by the dynamics of compact, magnetized neutron stars around...
We perform the first numerical simulations of a thin accretion disc in pseudo-potential for Reissner-Nordstrom naked singularity. The obtained results share the positions of the zero gravity sphere and maximal rotational velocity with the analytical solutions and the general relativistic simulations. They also show the characteristic shape of the
innermost part of the disc, matching the...
[Abstract][1]
Non-Spherically Symmetric Models of Compact Objects with the Salpeter Equation of State
This research explores the gravitational behavior of compact astronomical bodies, such as white dwarfs and neutron stars, under the framework of Einstein's general relativity. A simplified mathematical model incorporating the quadrupole moment to a first-order approximation is applied...
Using a renormalization-inspired perturbation expansion we show that oscillons in a generic field theory in (1+1)-dimensions arise as dressed $Q$-balls of a universal complex field theory. This theory is very close to the integrable complex sine-Gordon model which possesses exact multi-$Q$-balls. We show that excited oscillons, with their characteristic amplitude modulations, are two-oscillons...
Pions play an essential role in the strong interactions experienced by nucleons, the main components of the nuclear matter occurring in neutron stars or supernova explosions. The main problem regarding pions is how to implement them in the equations of state to properly incorporate the additional pion abundance, pressure, energy, and potential occurrence of the pion condensate. In my talk, I...
Multi-messenger signals of gravitational waves and neutrinos from supernovae carry information about properties of supernova cores, which cannot be directly observed with electromagnetic waves. To maximize impacts of future detection of these multi-messenger signals, it is important to understand the relationship between the characteristics of the multi-messenger signals and the properties of...
The Event Horizon Telescope (EHT) recently enabled imaging two supermassive black holes, M87 and Sagittarius A*, with the near event horizon scale resolution. Since the observed emission originates very close to the black hole, where trajectories of photons are subject to large deflection related to spacetime curvature, we can use these observations to test gravity in the strong regime....
We present general-relativistic hydrodynamical simulation results of accretion from an orbiting accretion torus (with a cusp) onto a Reissner-Nordström (RN) black hole and a RN naked singularity. The results could not be more different for the two cases. For a black hole, just as in the familiar Kerr/Schwarzschild case, matter overflowing the cusp plunges into the black hole horizon. For the...
Type-C QPOs in low-mass X-ray binaries are most commonly explained by the Lense-Thirring precession of the innermost hot and geometrically-thick component of the accretion flow. Most models however ignores any influence of the outer cold geometrically-thin accretion disk. We will discuss how this simple picture changes when the accretion torque by the outer disk is taken into account.
In this talk I shall present the mass twins compact star phenomenon together with the idea behind their existence and the motivation for searches. I will briefly review the special features in the equation of state (EoS) of the twins as well as their properties as compact stars. Such macroscopical properties can be tested with state-of-the-art multi-messenger astronomical observations. I will...
We are studying the evolution of multiple tori structures with 3D GRMHD simulations. The output from the simulations can be used in post-processing analysis to create synthetic ray-tracing images using well-known tools. Here I present our latest simulation results and their optical properties.
Accreting stellar-mass black holes in X-ray binaries (XRBs) exhibit different states, each characterized by distinct spectral properties. The two fundamental states are the high/soft state, dominated by the thermal multi-color blackbody emission from the accretion disk, and the low/hard state, dominated by non-thermal, power-law-like Comptonization emission originating from the hot corona....
A thin circular structure vibrating in the central plane of a black hole will be investigated. This circular ring (string loop) can be considered a simplified model for thin magnetic flux tubes (plasma physics), and connections to accreting fluid structures around the black hole will be demonstrated. The stability of the string loop and the frequencies of its vibrational modes will be provided...
We investigate the time evolution of two-dimensional sub-Keplerian transonic accretion flow onto a non-rotating black hole. We simulate the shocked accretion flow by using boundary values from semi-analytical analysis. Our focus is primarily on the regime of viscosity parameters that exhibit shock oscillation within the disc. By varying both viscosity and radiation cooling, we explore the...
We study a global, two-dimensional (2D) general relativistic magnetohydrodynamics (GRMHD) simulation of an accreting torus around a non-rotating black hole using Athena++. Our initial configuration is threaded with a net-vertical magnetic flux. This study investigates the effects of initial field strength onto the disk dynamics. We find that the initial net vertical magnetic field...
Through numerical simulations, we investigated accreting neutron stars with apparent luminosities consistent with ultraluminous X-ray sources (ULXs). We examined the effects of magnetic field strength and accretion rate using the radiative general relativistic magnetohydrodynamics code, Koral. Our findings show that the power of outflows increases as the magnetic dipole strength decreases and...
We present a brief introduction to cosmic inflation in the framework of Palatini gravity, which provides an intriguing alternative to the conventional metric formulation of gravity. In the latter, only the metric specifies the spacetime geometry, whereas in the former, the metric and the spacetime connection are treated as independent variables-an option that can result in a gravity theory...
Accretion mechanism is one of the most effcient process by which the gravitational potential energy of the matter can be converted into energy. This phenomenon is responsible for the exotic processes happening in the Universe. It provides us with an explanation of the huge amount of energy liberated and high luminosities observed in AGN's, X-ray binaries, etc. Therefore, modelling these...
Join us for an engaging public talk in the Unisphere Room at the Institute of Physics.
General relativistic magnetohydrodinamic (GRMHD) simulations feature dynamics of turbulence and mixing instabilities that become resolved only at higher grid densities. We determine the minimal resolution requirements that are adequate to determine underlining physical processes based on the results of theoretical model of accretion and simulations.
The effect of general relativity on the light curves from a system of neutron stars, boundary layers and disks
We analyze the impact of individual relativistic effects on the X-ray flux of low-mass X-ray binaries containing a neutron star. We compare the results of the relativistic raytracing code with calculations in Newtonian geometry.