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Current models of the spectrum of X-rays reflected from accretion disks around black holes and other compact objects are commonly calculated assuming that the density of the disk atmosphere is constant within several Thomson depths from the…

The close neighbourhood of a supermassive black hole contains not only the accreting gas and dust but also stellar-sized objects, such as late-type and early-type stars and compact remnants that belong to the nuclear star cluster. When…

Context. Many low-redshift active galactic nuclei harbor a supermassive black hole accreting matter at low or medium rates. At such rates, the accretion flow usually consists of a cold optically thick disk, plus a hot, low density,…

Direct-imaging surveys have looked for accreting planets through their accretion tracers such as H alpha but have been less fruitful than expected. However, up to now, hydrogen-line emission at accreting planets has been estimated primarily…

Magnetic field behaviour in a spherically-symmetric accretion flow for parameters typical of single black holes in the Galaxy is discussed. It is shown that in the majority of Galaxy volume, accretion onto single stellar-mass black holes…

The accretion of matter onto celestial bodies like black holes and neutron stars is a natural phenomenon that releases up to $40\%$ of the matter's rest-mass energy, which is considered a source of radiation. In active galactic nuclei and…

We report on the first phase of our study of slightly rotating accretion flows onto black holes. We consider inviscid accretion flows with a spherically symmetric density distribution at the outer boundary, but with spherical symmetry…

We calculate the temperature and ionization balance in an outflow from an accreting black hole under illumination by hard radiation from the central object. Electron scattering of the Fe K_alpha photons within the highly ionized expanding…

The Event Horizon Telescope (EHT) imaging of the supermassive black holes at the centers of Messier 87 galaxy and the Milky Way galaxy marks a significant step in observing the photon rings and central brightness depression that define the…

The black holes in the Event Horizon Telescope sources Messier 87* and Sagittarius A* (SgrA*) are embedded in a hot, collisionless plasma that is fully described in kinetic theory yet is usually modeled as an ideal, magnetized fluid. In…

Black holes (BHs) are believed to be a key ingredient of galaxy formation. However, the galaxy-BH interplay is challenging to study due to the large dynamical range and complex physics involved. As a consequence, hydrodynamical cosmological…

This study investigates the accretion process and observational signatures of thin accretion disks around a Schwarzschild black hole (BH) embedded in a Dehnen-type dark matter (DM) halo. We examine the influence of the density {\rho}_{s}…

The Event Horizon Telescope (EHT) provides a unique opportunity to probe the physics of supermassive black holes through Very Large Baseline Interferometry (VLBI), such as the existence of the event horizon, the accretion processes as well…

We investigate time-dependent inviscid hydrodynamical accretion flows onto a black hole using numerical simulations. We consider the accretion that consists of hot tenuous gas with low specific angular momentum and cold dense gas with high…

Chaotic cold accretion (CCA) profoundly differs from classic black hole accretion models. Using 3D high-resolution simulations, we probe the impact of rotation on the hot and cold accretion flow in a typical massive galaxy. In the hot mode,…

The study of radiation emitted from black hole accretion discs represents a crucial way to understand the main physical properties of these sources, and in particular the black hole spin. Beside spectral analysis, polarimetry is becoming…

We explore the evolution in power of black holes of all masses, and their associated jets, within the scheme of an accretion rate-dependent state transition. Below a critical value of the accretion rate all systems are assumed to undergo a…

We show scenarios in which primordial black hole accretion under the magnetorotational instability (MRI) uniquely relates the density of the early Universe to the abundance of present day dark matter. We demonstrate via long duration…

We use a suite of cosmological hydrodynamic simulations to quantify the accretion rates of baryons into dark matter halos and the resulting baryon mass fractions, as a function of halo mass, redshift, and baryon type (including cold and hot…

Sub-solar mass black holes could show up in gravitational wave observations in future and near-solar mass black holes might have been involved in the events GW190425 and GW190814. Since they cannot form from the stellar evolution, their…