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Observational Evidence for Black Holes
Ramesh Narayan, Jeffrey E. McClintock
Astronomers have discovered two populations of black holes: (i) stellar-mass black holes with masses in the range 5 to 30 solar masses, millions of which are present in each galaxy…
A High-Frequency Doppler Feature in the Power Spectra of Simulated GRMHD Black Hole Accretion Disks
Sarah Wellons, Yucong Zhu, Dimitrios Psaltis +2
Black hole binaries exhibit a wide range of variability phenomena, from large-scale state changes to broadband noise and quasi-periodic oscillations, but the physical nature of muc…
Numerical simulations of super-critical black hole accretion flows in general relativity
A. Sadowski, R. Narayan, J. C. McKinney +1
A new general relativistic radiation magnetohydrodynamical code KORAL, is described, which employs the M1 scheme to close the radiation moment equations. The code has been successf…
A new equilibrium torus solution and GRMHD initial conditions
Robert F. Penna, Akshay Kulkarni, Ramesh Narayan
General relativistic magnetohydrodynamic (GRMHD) simulations are providing influential models for black hole spin measurements, gamma ray bursts, and supermassive black hole feedba…
Confirmation Via the Continuum-Fitting Method that the Spin of the Black Hole in Cygnus X-1 is Extreme
Lijun Gou, Jeffrey E. McClintock, Ronald A. Remillard +6
In Gou et al. (2011), we reported that the black hole primary in the X-ray binary Cygnus X-1 is a near-extreme Kerr black hole with a spin parameter a*>0.95(3σ). We confirm this re…
General Relativistic Magnetohydrodynamic Simulations of Blandford-Znajek Jets and the Membrane Paradigm
Robert F. Penna, Ramesh Narayan, Aleksander Sadowski
Recently it has been observed that the scaling of jet power with black hole spin in galactic X-ray binaries is consistent with the predictions of the Blandford-Znajek (BZ) jet mode…
Thermal Stability in Turbulently Mixed Accretion Discs
Yucong Zhu, Ramesh Narayan
The standard thin accretion disc model predicts that discs around stellar mass black holes become radiation pressure dominated and thermally unstable once their luminosity exceeds…
Location of the bow shock ahead of cloud G2 at the Galactic Center
A. Sadowski, R. Narayan, L. Sironi +1
We perform detailed magnetohydrodynamic simulations of the gas cloud G2 interacting with the accretion flow around the Galactic Center black hole Sgr A*. We take as our initial con…
Energy Extraction from Spinning Black Holes via Relativistic Jets
Ramesh Narayan, Jeffrey E. McClintock, Alexander Tchekhovskoy
It has for long been an article of faith among astrophysicists that black hole spin energy is responsible for powering the relativistic jets seen in accreting black holes. Two rece…
Black Hole Spin via Continuum Fitting and the Role of Spin in Powering Transient Jets
Jeffrey E. McClintock, Ramesh Narayan, James F. Steiner
The spins of ten stellar black holes have been measured using the continuum-fitting method. These black holes are located in two distinct classes of X-ray binary systems, one that…
Semi-implicit scheme for treating radiation under M1 closure in general relativistic conservative fluid dynamics codes
Aleksander Sadowski, Ramesh Narayan, Alexander Tchekhovskoy +1
A numerical scheme is described for including radiation in multi-dimensional general-relativistic conservative fluid dynamics codes. In this method, a covariant form of the M1 clos…
Radio light curves during the passage of cloud G2 near Sgr A*
A. Sadowski, L. Sironi, D. Abarca +3
We calculate radio light curves produced by the bow shock that is likely to form in front of the G2 cloud when it penetrates the accretion disk of Sgr A*. The shock acceleration of…