The so-called “stationary” Hα line of SS433 is shown to consist of three components. A broad component is identified as emitted in that wind from the accretion disc which grows in speed with elevation above the plane of the disc. There are two narrow components, one permanently redshifted and the other permanently to the blue. These are remarkably steady in wavelength and must be emitted from a...

In this note we study the accretion disc that arises in hypercritical accretion of Ṁ ∼ 10 MEdd onto a neutron star while it is in common envelope evolution with a massive companion. Such a study was carried out by Chevalier (1996), who had earlier suggested that the neutron star would go into a black hole in common envelope evolution. In his later study he found that the accretion could possibl...

The soft excess seen in the X–ray spectra of many AGN can be well modelled by reflection from a partially ionised accretion disc. However, this often requires extreme parameters, both in terms of the underlying spacetime and the reflection geometry. An alternative model uses similarly partially ionised, velocity smeared material but from an accretion disc wind seen in absorption. We explicitly ...

Accretion onto black holes in wind-fed binaries and in collapsars forms small rotating discs with peculiar properties. Such “mini-discs” accrete on the free-fall time without help of viscosity and nevertheless can have a high radiative efficiency. The inviscid mini-disc model was previously constructed for a non-rotating black hole. We extend the model to the case of a spinning black hole, calc...

Using a one-dimensional height integrated model, we calculate the evolution of an unequal mass binary black hole with a coplanar gas disc that contains a gap due to the presence of the secondary black hole. Viscous evolution of the outer circumbinary disc initially hardens the binary, while the inner disc drains onto the primary (central) black hole. As long as the inner disc remains cool and t...

We compute the effect of an orbiting gas disc in promoting the coalescence of a central supermassive black hole binary. Unlike earlier studies, we consider a finite mass of gas with explicit time dependence: we do not assume that the gas necessarily adopts a steady state or a spatially constant accretion rate, i.e. that the merging black hole was somehow inserted into a pre–existing accretion d...

We present time-dependent simulations of a two-phase accretion flow around a black hole. The accretion flow initially is composed of an optically thick and cool disc close to the midplane, while on top and below the disc there is a hot and optically thin corona. We consider several interaction mechanisms as heating of the disc by the corona and Compton cooling of the corona by the soft photons ...

The dynamics of two massive black holes in a rotationally supported nuclear disc of mass Mdisc = 10 8M⊙ is explored using N-Body/SPH simulations. Gas and star particles are co–present in the disc. Described with a Mestel profile, the disc has a vertical support provided by turbulence of the gas, and by stellar velocity dispersion. A primary black hole of mass 4 × 106M⊙ is placed at the centre o...

If supermassive black holes in centres of galaxies form by merging of black-hole remnants of massive Population III stars, then there should be a few black holes of mass one or two orders of magnitude smaller than that of the central ones, orbiting around the centre of a typical galaxy. These black holes constitute a weak perturbation in the gravitational potential, which can generate wave phen...

The X-ray spectra of Galactic binary systems dominated by a quasi-thermal component (disc dominated or high/soft state) are well described by a standard ShakuraSunyaev disc structure down to the last stable orbit around the black hole. This is not the case in the very high (or steep power law) state, where the X-ray spectra show both a strong disc component and strong, steep tail to higher ener...