The inner region of the accretion disk around a magnetized star (T Tauri star, white dwarf or neutron star) is subjected to magnetic torques that induce warping and precession of the disk. These torques arise from the interaction between the stellar field and the induced electric currents in the disk. We carry out numerical simulations of the nonlinear evolution of warped, viscous accretion dis...

We present time-dependent models of the remnant accretion disks created during compact object mergers, focusing on the energy available from accretion at late times and the composition of the disk and its outflows. We calculate the dynamics near the outer edge of the disk, which contains the majority of the disk’s mass and determines the accretion rate onto the central black hole. This treatmen...

We critically examine issues associated with determining the fundamental properties of the black hole and the surrounding accretion disk in an X-ray binary based on modeling the disk X-ray continuum of the source. We base our work mainly on two XMM-Newton observations of GX 339−4, because they provided high-quality data at low energies (below 1 keV) which are critical for reliably modeling the ...

We compare the accretion flow onto the neutron star induced by Roche lobe overflow with that by the overflow from the Be disk, in a zero eccentricity, short period binary with the same mass transfer rate, performing three-dimensional Smoothed Particle Hydrodynamics simulations. We find that a persistent accretion disk is formed around the neutron star in both cases. The circularization radius o...

We critically assess the role of the Blandford-Znajek mechanism in the powering of outflows from accretion disk-fed black holes. We argue that there is no reason to suppose that the magnetic field threading the central spinning black hole differs significantly in strength from that threading the central regions of the disk. In this case, we show that the electromagnetic output from the inner di...

The bright X-ray binary pulsar Hercules X-1 has a 35-day cycle in hard x-ray intensity: ”Main High state – low state – Short High state – low state”. This is caused by a tilted-twisted precessing accretion disk. What is less well known is that during low states the soft x-rays and extreme ultraviolet radiation are modulated at the orbital period . This radiation is mainly due to reflection off ...

We analyze the wavelength-dependent variability of a sample of spectroscopically confirmed active galactic nuclei (AGN) selected from near-UV (NUV ) variable sources in the GALEX Time Domain Survey that have a large amplitude of optical variability (difference-flux S/N > 3) in the Pan-STARRS1 Medium Deep Survey (PS1 MDS). By matching GALEX and PS1 epochs in 5 bands (NUV , gP1, rP1, iP1, zP1) in...

Although the occurrence of steady supercritical disk accretion onto a black hole has been speculated about since the 1970s, it has not been accurately verified so far. For the first time, we previously demonstrated it through two-dimensional, long-term radiation-hydrodynamic simulations. To clarify why this accretion is possible, we quantitatively investigate the dynamics of a simulated supercr...

Aims. A simplified model of jet power from active galactic nuclei is proposed in which the relationship between jet power and disk luminosity is discussed by combining disk accretion with two mechanisms of extracting energy magnetically from a black hole accretion disk, i.e., the Blandford-Payne (BP) and the Blandford-Znajek (BZ) processes. Methods. By including the BP process into the conserva...

We present results from the first fully general relativistic, magnetohydrodynamic (MHD) simulations of an equal-mass black-hole binary (BHBH) in a magnetized, circumbinary accretion disk. We simulate both the pre- and postdecoupling phases of a BHBH-disk system and both "cooling" and "no-cooling" gas flows. Prior to decoupling, the competition between the binary tidal torques and the effective ...