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The collapsar model for gamma-ray bursts requires three essential ingredients: a massive core, removal of the hydrogen envelope, and enough angular momentum in the core. We study current massive star evolution models of solar metallicity to…
This paper continues the analysis of a set of general relativistic 3D MHD simulations of accreting tori in the Kerr metric with different black hole spins. We focus on bound matter inside the initial pressure maximum, where the…
We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neutron star and a mild…
Active Galactic Nuclei are powered by accretion of matter onto a supermassive black hole (SMBH) of mass Mbh ~ 10^{5}-10^{9} Msun. The accretion process is indeed the most efficient mechanism for energy release we currently know of, with up…
We calculate the structure and evolution of a gamma ray burst central engine where an accreting torus has formed around the newly born black hole. We study the general relativistic,MHD models and we self-consistently incorporate the nuclear…
Collapsars - rapidly rotating stellar cores that form black holes - can power gamma-ray bursts (GRBs) and are proposed to be key contributors to the production of heavy elements in the Universe via the rapid neutron capture process…
At the final stages of a supermassive black hole coalescence, the emission of gravitational waves will efficiently remove energy and angular momentum from the binary orbit, allowing the separation between the compact objects to shrink. In…
Context: Some apparently quiescent supermassive black holes (BHs) at centers of galaxies show quasi-periodic eruptions (QPEs) in the X-ray band, the nature of which is still unknown. A possible origin for the eruptions is an accretion disk,…
We follow the collapse in axisymmetry of a uniformly rotating, supermassive star (SMS) to a supermassive black hole (SMBH) in full general relativity. The initial SMS of arbitrary mass $M$ is marginally unstable to radial collapse and…
Isolated stellar-mass BH accrete gas, often at supersonic speeds, and can form outflows that can influence the accreted gas. The latter process, known as mechanical feedback, can significantly affect the accretion rate. We use…
We propose a novel mechanism for powering the central engines of Active Galactic Nuclei through super-critical (type II) black hole collapse. In this picture, ~$10^3 M_\odot$ of material collapsing at relativistic speeds can trigger a…
The merger process of a binary black hole system can have a strong impact on a circumbinary disk. In the present work we study the effect of both central mass reduction (due to the energy loss through gravitational waves) and a possible…
The theory of coronal evaporation predicts the formation of an inner hole in the cool thin accretion disk for mass accretion rates below a certain value (~ 1/50 of the Eddington mass accretion rate) and the sudden disappearance of this hole…
The binary-driven hypernova (BdHN) model proposes long gamma-ray bursts (GRBs) originate in binaries composed of a carbon-oxygen (CO) star and a neutron star (NS) companion. The CO core collapse generates a newborn NS and a supernova that…
Rapid inflows associated with early galaxy formation lead to the accumulation of self-gravitating gas in the centers of proto-galaxies. Such gas accumulations are prone to non-axisymmetric instabilities, as in the well-known Maclaurin…
We present a new way of looking at the very long term evolution of GRBs in which the disk of material surrounding the putative black hole powering the GRB jet modulates the mass flow, and hence the efficacy of the process that extracts…
The accretion of hot slowly rotating gas onto a supermassive black hole is considered. Rotation velocities at the Bondi radius r_B are small in comparison with speed of sound c_s. The centrifugal barrier at a depth r_c = l^2/G M_BH << r_B…
We study the gravitational collapse of a rotating supermassive star (SMS) by means of a (3+1) hydrodynamical simulation in a post-Newtonian (PN) approxi- mation of general relativity. This problem is particularly challenging because of the…
Accretion on to seed black holes (BHs) is believed to play a crucial role in formation of supermassive BHs observed at high-redshift (z>6). Here, we investigate the combined effect of gas angular momentum and radiation feedback on the…
Rapidly spinning, strongly magnetized proto-neutron stars ("millisecond proto-magnetars") are candidate central engines of long-duration gamma-ray bursts (GRB), superluminous supernovae (SLSNe), and binary neutron star mergers. Magnetar…