We show that puncture data for quasicircular binary black hole orbits allow a special gauge choice that realizes some of the necessary conditions for the existence of an approximate helical Killing vector field. Introducing free parameters for the lapse at the punctures we can satisfy the condition that the Komar and ADMmass agree at spatial infinity. Several other conditions for an approximate...

Consider a team of asynchronous agents that must explore an unknown graph G in presence of a black hole, a node which destroys all incoming agents without leaving any observable trace. Interagent communication and coordination is achieved using tokens that agents can pick up, carry, and drop on the nodes. It is known that, if the agents have a map of G, the problem can be solved with a constant...

We investigate herein the spin interaction during collisions between Kerr-(anti-)de Sitter black holes. The spin interaction potential depends on the relative rotation directions of the black holes, and this potential can be released as gravitational radiation upon collision. The energy of the radiation depends on the cosmological constant and corresponds to the spin interaction potential in th...

A toy model for the Blandford-Znajek mechanism is investigated: a Kerr black hole with a toroidal electric current residing in a thin disk around the black hole in the equatorial plane. The toroidal electric current generates a poloidal magnetic field threading the black hole and disk. The rotation of the black hole and disk relative to the magnetic field induces an electromotive force, which c...

Accretion on to supermassive black holes (SMBHs) in galaxy formation simulations is frequently modelled by the Bondi–Hoyle formalism. Here we examine the validity of this approach analytically and numerically. We argue that the character of the flow where one evaluates the gas properties is unlikely to satisfy the simple Bondi–Hoyle model. Only in the specific case of hot virialized gas with ze...

We calibrate reverberation-based black hole (BH) masses in active galactic nuclei (AGNs) by using the correlation between BH mass,MBH, and bulge/spheroid stellar velocity dispersion, . We use new measurements of for six AGNs and published velocity dispersions for 10 others, in conjunction with improved reverberationmapping results, to determine the scaling factor required to bring reverberation...

The objectivity of black hole entropy is discussed in the particular case of a Schwarzchild black hole. Using Jaynes' maximum entropy formalism and Euclidean path integral evaluation of partition function , it is argued that in the semiclassical limit when the fluctutation of metric is neglected, the black hole entropy of a Schwarzchild black hole is equal to the maximal information entropy of ...

A partially first-order form of the characteristic formulation is introduced to control the accuracy in the computation of gravitational waveforms produced by highly distorted single black hole spacetimes. Our approach is to reduce the system of equations to first-order differential form on the angular derivatives, while retaining the proven radial and time integration schemes of the standard c...

We study a revised version of Witten’s 2d black hole, in which the matter and (b, c) ghosts are mixed. The level of the coset model is still 9/4. We show that this model is equivalent to that of Mukhi and Vafa, in which the level of the coset model is taken as 3, and the stress tensor is improved. We argue that the exact metric in such a model is just the semi-classical one, quite different fro...