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The formation and growth of supermassive black holes is a key issue to unveil the secrets of galaxy formation. In particular, the gravitational recoil produced in the merger of unequal mass black hole binaries could have a number of…
Supermassive stars (SMSs) collapsing via the general-relativistic (GR) instability are invoked as the possible progenitors of supermassive black holes. Their mass and angular momentum at the onset of the instability are key in many…
The motion of a black hole about the centre of gravity of its host galaxy induces a strong response from the surrounding stellar population. We treat the case of a harmonic potential analytically and show that half of the stars on circular…
Gravitational waves from the coalescence of binary black holes carry linear momentum, causing center of mass recoil. This ``radiation rocket'' has important implications for systems with escape speeds of order the recoil velocity. We…
In this paper, we consider the gravitational radiation generated by the collision of highly relativistic particles with rotating Kerr black holes. We use the Sasaki-Nakamura formalism to compute the waveform, energy spectra and total energy…
Sari and Piran have demonstrated that the time structure of gamma-ray bursts must reflect the time structure of their energy release. A model which satisfies this condition uses the electrodynamic emission of energy by the magnetized…
The influence of rotation on the dynamical evolution of collisional stellar systems is investigated by solving the orbit-averaged Fokker-Planck equation in (E,J_z)-space. We find that large amounts of initial rotation drive the system into…
We present the gravitational-wave flux balance law in an extreme mass-ratio binary with a spinning secondary. This law relates the flux of energy (angular momentum) radiated to null infinity and through the event horizon to the local change…
We study the physics behind the neutrino-driven mechanism for gamma-ray bursts and hypernovae, deriving the critical density at which these outbursts occur in the collapsar model. The agreement between this derivation and results from past…
I review the rotation measurements of accreting neutron stars. Many of the highly magnetic accreting X-ray pulsars have been continuously observed with the Burst and Transient Source Experiment (BATSE) aboard the Compton Gamma-Ray…
We calculate new evolutionary models of rotating primordial very massive stars, with initial mass from $100\,M_{\odot}$ to $200\,M_{\odot}$, for two values of the initial metallicity ${Z=0}$ and ${Z=0.0002}$. For the first time in this mass…
We present a reanalysis of the outburst radial velocity data for X-Ray Nova Scorpii 1994. Using a model based on X-ray heating of the secondary star we suggest a more realistic treatment of the radial velocity data. Solutions are obtained…
We present here a new determination of the ratio of energies radiated by active galactic nuclei and by stars and discuss the reasons for the apparently conflicting results found in previous studies. We conclude that the energy radiated by…
The internal rotation and magnetism of evolved massive stars are considered in response to i) the inward pumping of angular momentum through deep and slowly rotating convective layers; and ii) the winding up of a helical magnetic field in…
We consider the explosion of supernovae and the possible production of a variety of high energy transients by delayed black hole formation in massive stars endowed with rotation. Following the launch of a ``successful'' shock by the usual…
We investigate the behavior of a radiating Schwarzschild black hole toy-model in a 2D noncommutative spacetime. It is shown that coordinate noncommutativity leads to: i) the existence of a minimal non-zero mass to which black hole can…
The core rotation rates of massive stars have a substantial impact on the nature of core-collapse supernovae and their compact remnants. We demonstrate that internal gravity waves (IGW), excited via envelope convection during a red…
Recent three dimensional, high-resolution simulations of neutron star coalescences are analysed to assess whether short gamma-ray bursts (GRBs) could originate from such encounters. The two most popular modes of energy extraction -- namely…
We study the low angular momentum accretion of matter onto Schwarzschild or Kerr black hole using fully relativistic numerical simulations. Our aim is to include the rotation of both the gas and the black hole and the presence of the…
The formation of the most massive quasars observed at high redshifts requires extreme inflows of gas down to the length scales of the central compact object. Here, we estimate the maximum inflow rate allowed by gravity down to the surface…