75 research outputs found
The Distribution and Annihilation of Dark Matter Around Black Holes
We use a Monte Carlo code to calculate the geodesic orbits of test particles
around Kerr black holes, generating a distribution function of both bound and
unbound populations of dark matter particles. From this distribution function,
we calculate annihilation rates and observable gamma-ray spectra for a few
simple dark matter models. The features of these spectra are sensitive to the
black hole spin, observer inclination, and detailed properties of the dark
matter annihilation cross section and density profile. Confirming earlier
analytic work, we find that for rapidly spinning black holes, the collisional
Penrose process can reach efficiencies exceeding , leading to a
high-energy tail in the annihilation spectrum. The high particle density and
large proper volume of the region immediately surrounding the horizon ensures
that the observed flux from these extreme events is non-negligible.Comment: accepted to Ap
Electromagnetic Counterparts to Black Hole Mergers
During the final moments of a binary black hole (BH) merger, the
gravitational wave (GW) luminosity of the system is greater than the combined
electromagnetic output of the entire observable universe. However, the
extremely weak coupling between GWs and ordinary matter makes these waves very
difficult to detect directly. Fortunately, the inspiraling BH system will
interact strongly--on a purely Newtonian level--with any surrounding material
in the host galaxy, and this matter can in turn produce unique electromagnetic
(EM) signals detectable at Earth. By identifying EM counterparts to GW sources,
we will be able to study the host environments of the merging BHs, in turn
greatly expanding the scientific yield of a mission like LISA.Comment: 10 pages, 1 figure, submitted to Class. Quantum Grav. special issue:
proceedings of 8th LISA Symposiu
Astrophysics of Super-massive Black Hole Mergers
We present here an overview of recent work in the subject of astrophysical
manifestations of super-massive black hole (SMBH) mergers. This is a field that
has been traditionally driven by theoretical work, but in recent years has also
generated a great deal of interest and excitement in the observational
astronomy community. In particular, the electromagnetic (EM) counterparts to
SMBH mergers provide the means to detect and characterize these highly
energetic events at cosmological distances, even in the absence of a
space-based gravitational-wave observatory. In addition to providing a
mechanism for observing SMBH mergers, EM counterparts also give important
information about the environments in which these remarkable events take place,
thus teaching us about the mechanisms through which galaxies form and evolve
symbiotically with their central black holes.Comment: Invited article for the focus issue on astrophysical black holes in
Classical and Quantum Gravity, guest editors: D. Merritt and L. Rezzoll
A Hot Spot Model for Black Hole QPOs
In at least two black hole binary systems, the Rossi X-Ray Timing Explorer
has detected high frequency quasi-periodic oscillations (HFQPOs) with a 2:3
frequency commensurability. We propose a simple hot spot model to explain the
positions, amplitudes, and widths of the HFQPO peaks. Using the exact geodesic
equations for the Kerr metric, we calculate the trajectories of massive test
particles, which are treated as isotropic, monochromatic emitters in their rest
frames. By varying the hot spot parameters, we are able to explain the
different features observed in ``Type A'' and ``Type B'' QPOs from XTE
J1550-564. In the context of this model, the observed power spectra allow us to
infer values for the black hole mass and angular momentum, and also constrain
the parameters of the model.Comment: 4 pages, 2 figures, to be published in X-Ray Timing 2003: Rossi and
Beyond, ed. P. Kaaret, F. K. Lamb, & J. H. Swank (Melville, NY: American
Institute of Physics
Black Hole Coalescence: The Gravitational Wave Driven Phase
When two supermassive black holes (SMBHS) approach within 1-10 mpc, gravitational wave (GW) losses begin to dominate the evolution of the binary, pushing the system to merge in a relatively small time. During this final inspiral regime, the system will emit copious energy in GWs, which should be directly detectable by pulsar timing arrays and space-based interferometers. At the same time, any gas or stars in the immediate vicinity of the merging 5MBHs can get heated and produce bright electromagnetic (EM) counterparts to the GW signals. We present here a number of possible mechanisms by which simultaneous EM and GW signals will yield valuable new information about galaxy evolution, accretion disk dynamics, and fundamental physics in the most extreme gravitational fields
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