13 research outputs found
Estimating masses of Keplerian disk systems: the case of AGN in NGC 4258
The Keplerian motion of accretion disks in Active Galactic Nuclei (AGN) is
usually believed to be generated by a heavy central mass. We investigate
accreting disk systems with polytropic gas in Keplerian rotation and obtain a
phenomenological formula that relates the Keplerian angular frequency to the
ratio of disk and central masses. Central mass approaches the Keplerian value,
if the inner boundary of a disk is close to the minimal stable orbit of a black
hole. These results are applied to NGC 4258, the unique AGN with a finely
measured Keplerian rotation curve of the central disk, with the conclusion that
its rotation curve is, in fact, determined by the central black hole. The mass
of the accretion disk exceeds 100 solar masses.Comment: 7 pages, 2 figures, to appear in Acta Phys. Pol.
General-relativistic rotation: self-gravitating fluid tori in motion around black holes
We obtain from the first principles a general-relativistic Keplerian rotation
law for self-gravitating disks around spinning black holes. This is an
extension of a former rotation law that was designed mainly for toroids around
spin-less black holes. We integrate numerically axial stationary Einstein
equations with self-gravitating disks around spinless or spinning black holes;
that includes the first ever integration of the Keplerian selfgravitating tori.
This construction can be used for the description of tight black hole-torus
systems produced during coalescences of two neutron stars or modelling of
compact active galactic nuclei.Comment: Matches published versio
Self-gravitating magnetised tori around black holes in general relativity
We investigate stationary, self-gravitating, magnetised disks (or tori)
around black holes. The models are obtained by numerically solving the coupled
system of the Einstein equations and the equations of ideal
general-relativistic magnetohydrodynamics. The mathematical formulation and
numerical aspects of our approach are similar to those reported in previous
works modeling stationary self-gravitating perfect-fluid tori, but the
inclusion of magnetic fields represents a new ingredient. Following previous
studies of purely hydrodynamical configurations, we construct our models
assuming Keplerian rotation in the disks and both spinning and spinless black
holes. We focus on the case of a toroidal distribution of the magnetic field
and build a large set of models corresponding to a wide range of values of the
magnetisation parameter, starting with weakly magnetised disks and ending at
configurations in which the magnetic pressure dominates over the thermal one.
In all our models, the magnetic field affects the equilibrium structure of the
torus mainly due to the magnetic pressure. In particular, an increasing
contribution of the magnetic field shifts the location of the maximum of the
rest-mass density towards inner regions of the disk. The total mass of the
system and the angular momentum are affected by the magnetic field in a complex
way, that depends on the black hole spin and the location of the inner radius
of the disk. The non-linear dynamical stability of the solutions presented in
this paper will be reported elsewhere.Comment: 17 pages, 5 figures, 1 tabl
Analytical and Numerical Analysis of Circumbinary Disk Dynamics -- I: Coplanar Systems
We present an analytical and numerical study of a system composed of a
stellar binary pair and a massless, locally isothermal viscous accretion disk
that is coplanar to the binary orbital plane. Analytically, we study the effect
of the binary's gravitational potential over short timescales through the study
of stability for epicyclic orbits, and over long timescales by revisiting the
concept of resonant torques. Numerically, we perform two-dimensional Newtonian
numerical simulations of the disk-binary system over a range of binary mass
ratios. We find that the results of our simulations are consistent with
previous numerical studies. We additionally show, by comparison of the
analytical and numerical results, that the circumbinary gap is maintained on
the orbital timescale through the driving of epicyclic instabilities, and does
not depend on resonant torquing, contrary to standard lore. While our results
are applicable to any disk-binary system, we highlight the importance of this
result in the search for electromagnetic and gravitational-wave signatures from
supermassive black-hole binaries
General-relativistic versus Newtonian: geometric dragging and dynamic anti-dragging in stationary disks in the first post-Newtonian approximation
We evaluate general-relativistic effects in motion of stationary accretion
disks around a Schwarzschild black hole, assuming the first post-Newtonian
(1PN) approximation. There arises an integrability condition, that leads to the
emergence of two types of general-relativistic corrections to a Newtonian
rotation curve. The well known geometric dragging of frames accelerates
rotation but the hitherto unknown dynamic term, that reflects the disk
structure, deccelerates rotation. The net result can diminish the Newtonian
angular velocity of rotation in a central disk zone but the geometric dragging
of frames dominates in the disk boundary zone. Both effects are nonlinear in
nature and they disappear in the limit of test fluids. Dust disks can be only
geometrically dragged while uniformly rotating gaseous disk are untouched at
the 1PN order. General-relativistic contributions can strongly affect rotation
periods in Keplerian motion for compact systems.Comment: Minor changes in the introduction and the summary. Accepted by the
Physical Review D. 12 pages, 5 figure
On the Mechanism of Action of SJ-172550 in Inhibiting the Interaction of MDM4 and p53
SJ-172550 (1) was previously discovered in a biochemical high throughput screen for inhibitors of the interaction of MDMX and p53 and characterized as a reversible inhibitor (J. Biol. Chem. 2010; 285∶10786). Further study of the biochemical mode of action of 1 has shown that it acts through a complicated mechanism in which the compound forms a covalent but reversible complex with MDMX and locks MDMX into a conformation that is unable to bind p53. The relative stability of this complex is influenced by many factors including the reducing potential of the media, the presence of aggregates, and other factors that influence the conformational stability of the protein. This complex mechanism of action hinders the further development of compound 1 as a selective MDMX inhibitor
The Santa Barbara Binary-Disk Code Comparison
International audienceWe have performed numerical calculations of a binary interacting with a gas disk, using eleven different numerical methods and a standard binary-disk setup. The goal of this study is to determine whether all codes agree on a numerically converged solution, and to determine the necessary resolution for convergence and the number of binary orbits that must be computed to reach an agreed-upon relaxed state of the binary-disk system. We find that all codes can agree on a converged solution (depending on the diagnostic being measured). The zone spacing required for most codes to reach a converged measurement of the torques applied to the binary by the disk is roughly 1% of the binary separation in the vicinity of the binary components. For our disk model to reach a relaxed state, codes must be run for at least 200 binary orbits, corresponding to about a viscous time for our parameters, binary orbits, where is the kinematic viscosity. We did not investigate dependence on binary mass ratio, eccentricity, disk temperature, or disk viscosity; therefore, these benchmarks may act as guides towards expanding converged solutions to the wider parameter space but might need to be updated in a future study that investigates dependence on system parameters. We find the most major discrepancies between codes resulted from the dimensionality of the setup (3D vs 2D disks). Beyond this, we find good agreement in the total torque on the binary between codes, although the partition of this torque between the gravitational torque, orbital accretion torque, and spin accretion torque depends sensitively on the sink prescriptions employed. In agreement with previous studies, we find a modest difference in torques and accretion variability between 2D and 3D disk models. We find cavity precession rates to be appreciably faster in 3D than in 2D
Structures of relevant compounds.
<p><b>Panel A.</b> Structure of SJ-172550 (<b>1</b>) and a non-reactive analog (<b>2</b>). <b>Panel B.</b> The potential mechanism of covalent adduct formation.</p
Inhibition of MDMX-p53 peptide binding by compound 1 (IC<sub>50</sub> = 3 µM), compound 2 (IC<sub>50</sub>>100 uM).
<p>Inhibition of MDMX-p53 peptide binding by compound 1 (IC<sub>50</sub> = 3 µM), compound 2 (IC<sub>50</sub>>100 uM).</p