368 research outputs found
Self Organization and a Dynamical Transition in Traffic Flow Models
A simple model that describes traffic flow in two dimensions is studied. A
sharp {\it jamming transition } is found that separates between the low density
dynamical phase in which all cars move at maximal speed and the high density
jammed phase in which they are all stuck. Self organization effects in both
phases are studied and discussed.Comment: 6 pages, 4 figure
Comment on the Black Hole Recoil Candidate Quasar SDSS J092712.65+294344.0
SDSS J092712.65+294344.0 has been proposed as a candidate for a supermassive
black hole (~10^8.8 solar masses) ejected at high speed from the host galactic
nucleus by gravitational radiation recoil, or alternatively for a supermassive
black hole binary. This is based on a blueshift of 2650 km/s of the broad
emission lines ("b-system") relative to the narrow emission lines ("r-system")
presumed to reflect the galaxy velocity. New observations with the Hobby-Eberly
Telescope (HET) confirm the essential features of the spectrum. We note a third
redshift system, characterized by weak, narrow emission lines of [O III] and [O
II] at an intermediate velocity 900 km/s redward of the broad line velocity
("i-system"). A composite spectrum of SDSS QSOs similar to J0927 illustrates
the feasibility of detecting the calcium K absorption line in spectra of
sufficient quality. The i-system may represent the QSO host galaxy or a
companion. Photoionization requires the black hole to be ~3 kpc from the
r-system emitting gas, implying that we are observing the system only 10^6 yr
after the recoil event and contributing to the low probability of observing
such a system. The HET observations give an upper limit of 10 km/s per year on
the rate of change of the velocity difference between the r- and b-systems,
constraining the orbital phase in the binary model. These considerations and
the presence of a cluster of galaxies apparently containing J0927 favor the
idea that this system represents a superposition of two AGN.Comment: 18 pages, 4 figures, ApJ in press, revised discussion of stellar
absorption features and binary black hole mode
Anatomy of the binary black hole recoil: A multipolar analysis
We present a multipolar analysis of the gravitational recoil computed in recent numerical simulations of binary black hole (BH) coalescence, for both unequal masses and non-zero, non-precessing spins. We show that multipole moments up to and including l=4 are sufficient to accurately reproduce the final recoil velocity (within ~2%) and that only a few dominant modes contribute significantly to it (within ~5%). We describe how the relative amplitudes, and more importantly, the relative phases, of these few modes control the way in which the recoil builds up throughout the inspiral, merger, and ringdown phases. We also find that the numerical results can be reproduced by an ``effective Newtonian'' formula for the multipole moments obtained by replacing the radial separation in the Newtonian formulae with an effective radius computed from the numerical data. Beyond the merger, the numerical results are reproduced by a superposition of three Kerr quasi-normal modes (QNMs). Analytic formulae, obtained by expressing the multipole moments in terms of the fundamental QNMs of a Kerr BH, are able to explain the onset and amount of ``anti-kick'' for each of the simulations. Lastly, we apply this multipolar analysis to help explain the remarkable difference between the amplitudes of planar and non-planar kicks for equal-mass spinning black holes
Interruption of Tidal Disruption Flares By Supermassive Black Hole Binaries
Supermassive black hole binaries (SMBHBs) are products of galaxy mergers, and
are important in testing Lambda cold dark matter cosmology and locating
gravitational-wave-radiation sources. A unique electromagnetic signature of
SMBHBs in galactic nuclei is essential in identifying the binaries in
observations from the IR band through optical to X-ray. Recently, the flares in
optical, UV, and X-ray caused by supermassive black holes (SMBHs) tidally
disrupting nearby stars have been successfully used to observationally probe
single SMBHs in normal galaxies. In this Letter, we investigate the accretion
of the gaseous debris of a tidally disrupted star by a SMBHB. Using both
stability analysis of three-body systems and numerical scattering experiments,
we show that the accretion of stellar debris gas, which initially decays with
time , would stop at a time . Here, and is the orbital period of the SMBHB.
After a period of interruption, the accretion recurs discretely at time , where . Both and sensitively
depend on the orbital parameters of the tidally disrupted star at the tidal
radius and the orbit eccentricity of SMBHB. The interrupted accretion of the
stellar debris gas gives rise to an interrupted tidal flare, which could be
used to identify SMBHBs in non-active galaxies in the upcoming transient
surveys.Comment: 13 pages, including one color figure; typos corrected; appeared in
ApJ Letters (November 20 issue
Analytical time-like geodesics
Time-like orbits in Schwarzschild space-time are presented and classified in
a very transparent and straightforward way into four types. The analytical
solutions to orbit, time, and proper time equations are given for all orbit
types in the form r=r(\lambda), t=t(\chi), and \tau=\tau(\chi), where \lambda\
is the true anomaly and \chi\ is a parameter along the orbit. A very simple
relation between \lambda\ and \chi\ is also shown. These solutions are very
useful for modeling temporal evolution of transient phenomena near black holes
since they are expressed with Jacobi elliptic functions and elliptic integrals,
which can be calculated very efficiently and accurately.Comment: 15 pages, 10 figures, accepted by General Relativity and Gravitatio
Design and tests of the hard X-ray polarimeter X-Calibur
X-ray polarimetry promises to give qualitatively new information about
high-energy astrophysical sources, such as binary black hole systems,
micro-quasars, active galactic nuclei, and gamma-ray bursts. We designed, built
and tested a hard X-ray polarimeter X-Calibur to be used in the focal plane of
the InFOCuS grazing incidence hard X-ray telescope. X-Calibur combines a low-Z
Compton scatterer with a CZT detector assembly to measure the polarization of
10-80 keV X-rays making use of the fact that polarized photons Compton scatter
preferentially perpendicular to the electric field orientation. X-Calibur
achieves a high detection efficiency of order unity.Comment: 9 pages, 5 figures, conference proceedings: SPIE 2011 (San Diego
A new model for QPOs in accreting black holes: application to the microquasar GRS 1915+105
(abridged) In this paper we extend the idea suggested previously by Petri
(2005a,b) that the high frequency quasi-periodic oscillations observed in
low-mass X-ray binaries may be explained as a resonant oscillation of the
accretion disk with a rotating asymmetric background (gravitational or
magnetic) field imposed by the compact object. Here, we apply this general idea
to black hole binaries. It is assumed that a test particle experiences a
similar parametric resonance mechanism such as the one described in paper I and
II but now the resonance is induced by the interaction between a spiral density
wave in the accretion disk, excited close to the innermost stable circular
orbit, and vertical epicyclic oscillations. We use the Kerr spacetime geometry
to deduce the characteristic frequencies of this test particle. The response of
the test particle is maximal when the frequency ratio of the two strongest
resonances is equal to 3:2 as observed in black hole candidates. Finally,
applying our model to the microquasar GRS 1915+105, we reproduce the correct
value of several HF-QPOs. Indeed the presence of the 168/113/56/42/28 Hz
features in the power spectrum time analysis is predicted. Moreover, based only
on the two HF-QPO frequencies, our model is able to constrain the mass and angular momentum of the accreting black hole.Comment: Accepted for publication in Astrophysics & Space Scienc
Ruling Out Chaos in Compact Binary Systems
We investigate the orbits of compact binary systems during the final inspiral
period before coalescence by integrating numerically the second-order
post-Newtonian equations of motion. We include spin-orbit and spin-spin
coupling terms, which, according to a recent study by Levin [J. Levin, Phys.
Rev. Lett. 84, 3515 (2000)], may cause the orbits to become chaotic. To examine
this claim, we study the divergence of initially nearby phase-space
trajectories and attempt to measure the Lyapunov exponent gamma. Even for
systems with maximally spinning objects and large spin-orbit misalignment
angles, we find no chaotic behavior. For all the systems we consider, we can
place a strict lower limit on the divergence time t_L=1/gamma that is many
times greater than the typical inspiral time, suggesting that chaos should not
adversely affect the detection of inspiral events by upcoming
gravitational-wave detectors.Comment: 8 pages, 4 figures, submitted to Phys. Rev. Let
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