Related papers: Cyg X-3: can the compact object be a black hole?
Massive gas-rich galaxy discs at $z \sim 1-3$ host massive star-forming clumps with typical baryonic masses in the range $10^7-10^8$~M$_{\odot}$ which can affect the orbital decay and concurrent growth of supermassive black hole (BH) pairs.…
We identified a new X-ray transient CXOM31 004252.457+411631.17 (T13) in M31 during a 2013 June Chandra observation. This system is particularly exciting because it is located within 100" of M31*; it is thought that this region of the bulge…
There are many observational evidences for the detection of compact objects with masses significantly larger (in galactic cases) or much larger (in extragalactic cases) than the upper limits of masses of em cold Neutron Stars. Such compact…
With an X-ray stacking analysis of ~ 12, 000 Lyman-break galaxies (LBGs) using the Chandra Legacy Survey image, we investigate average supermassive black hole (SMBH) accretion properties of star-forming galaxies (SFGs) at 4 <~ z <~ 7.…
The accretion of matter onto black holes and neutron stars often leads to the launching of outflows that can greatly affect the environments surrounding the compact object. In supermassive black holes, these outflows can even be powerful…
Galactic stellar-population-synthesis models, chemical-enrichment models, and long-duration Bulge microlensing events indicate about N_tot=(0.1-1) billion stellar-mass black holes reside in our Galaxy. We study X-ray emission from accretion…
Globular star clusters contain thousands to millions of old stars packed within a region only tens of light years across. Their high stellar densities make it very probable that their member stars will interact or collide. There has been…
We examine the effect of an accretion disc on the orbits of stars in the central star cluster surrounding a central massive black hole by performing a suite of 39 high-accuracy direct N-body simulations using state-of-the art software and…
The black hole binary Cygnus X-1 has a 5.6 day orbital period. We first detected a clear intensity modulation with the orbital period in its high/soft state with 6 year MAXI data, as well as in its low/hard state. In the low/hard state, the…
Ultraluminous X-ray sources fed by Wolf-Rayet star winds and X-ray bursters in ultracompact binaries with He or C white dwarfs have accretion disks, whose properties may significantly differ from those of pure H alpha-accretion disks. We…
High-redshift ($z>2$) blazars, with relativistic jets aligned toward us, probe the most powerful end of the active galactic nuclei (AGN) population. We aim at determining the black hole masses and mass accretion rates of high-$z$ blazars in…
Gaia BH3 is the first observed dormant black hole (BH) with a mass of $\approx{30}$ M$_\odot$ and represents the first confirmation that such massive BHs are associated with metal-poor stars. Here, we explore the isolated binary formation…
We have analyzed the observed radial-velocity curve for the X-ray binary M33 X-7 in a Roche model. We have analyzed the dependence between the component masses and the degree of filling of the optical star's Roche lobe to obtain the ratio…
Recently, the issue of the role of the Eddington limit in accretion discs became a matter of debate. While the classical (spherical) Eddington limit is certainly an over-simplification, it is not really clear how to treat it in a flattened…
The mass density of massive black holes observed locally is consistent with the hard X-ray Background provided that most of the radiation produced during their growth was absorbed by surrounding gas. A simple model is proposed here for the…
As a first step towards understanding the angular momentum evolution history of black holes in merging black-hole/neutron-star binaries, we perform population synthesis calculations to track the distribution of accretion histories of…
We model non-thermal emission spectrum of the extremely sub-Eddington X-ray binary system A0620-00. It is believed that this non-thermal emission is produced by a radiatively inefficient "quiescent" accretion onto a stellar-mass black hole…
We show that black holes supplied with mass at hyper--Eddington rates drive outflows with mildly sub--relativistic velocities. These are $\sim 0.1 - 0.2c$ for Eddington accretion factors $\dot m_{\rm acc} \sim 10 - 100$, and $\sim…
We study X-ray spectra of Cyg X-3 from BeppoSAX, taking into account absorption and emission in the strong stellar wind of its companion. We find the intrinsic X-ray spectra are well modelled by disc blackbody emission, its upscattering by…
A supermassive black hole SgrA* with the mass ~4x10^6 Msun resides at the centre of our galaxy. Building up such a massive black hole within the ~10^10 year lifetime of our galaxy would require a mean accretion rate of ~4x10^-4 Msun/yr. At…