9,110 research outputs found
Spacetime and orbits of bumpy black holes
Our universe contains a great number of extremely compact and massive objects
which are generally accepted to be black holes. Precise observations of orbital
motion near candidate black holes have the potential to determine if they have
the spacetime structure that general relativity demands. As a means of
formulating measurements to test the black hole nature of these objects,
Collins and Hughes introduced "bumpy black holes": objects that are almost, but
not quite, general relativity's black holes. The spacetimes of these objects
have multipoles that deviate slightly from the black hole solution, reducing to
black holes when the deviation is zero. In this paper, we extend this work in
two ways. First, we show how to introduce bumps which are smoother and lead to
better behaved orbits than those in the original presentation. Second, we show
how to make bumpy Kerr black holes -- objects which reduce to the Kerr solution
when the deviation goes to zero. This greatly extends the astrophysical
applicability of bumpy black holes. Using Hamilton-Jacobi techniques, we show
how a spacetime's bumps are imprinted on orbital frequencies, and thus can be
determined by measurements which coherently track a small orbiting body's
orbital phase. We find that weak-field orbits of bumpy black holes are modified
exactly as expected from a Newtonian analysis of a body with a prescribed
multipolar structure, reproducing well-known results from the celestial
mechanics literature. The impact of bumps on strong-field orbits is especially
strong, suggesting that this framework will allow observations to set robust
limits on the extent to which a spacetime's multipoles deviate from the black
hole expectation.Comment: 24 pages, 3 figures, accepted to Phys. Rev. D. This version corrects
some typos and incorporates suggested edit
On the falloff of radiated energy in black hole spacetimes
The goal of much research in relativity is to understand gravitational waves
generated by a strong-field dynamical spacetime. Quantities of particular
interest for many calculations are the Weyl scalar , which is simply
related to the flux of gravitational waves far from the source, and the flux of
energy carried to distant observers, . Conservation laws guarantee
that, in asympotically flat spacetimes, and as . Most calculations extract these quantities at
some finite extraction radius. An understanding of finite radius corrections to
and allows us to more accurately infer their asymptotic
values from a computation. In this paper, we show that, if the final state of
the system is a black hole, then the leading correction to is , and that to the energy flux is --- not and as one might naively guess. Our argument only
relies on the behavior of the curvature scalars for black hole spacetimes.
Using black hole perturbation theory, we calculate the corrections to the
leading falloff, showing that it is quite easy to correct for finite extraction
radius effects.Comment: 5 pages, no figures, accepted to Phys. Rev. D. This version corrects
several typos and minor errors in the earlier submissio
Localizing coalescing massive black hole binaries with gravitational waves
Massive black hole binary coalescences are prime targets for space-based
gravitational wave (GW) observatories such as {\it LISA}. GW measurements can
localize the position of a coalescing binary on the sky to an ellipse with a
major axis of a few tens of arcminutes to a few degrees, depending on source
redshift, and a minor axis which is times smaller. Neglecting weak
gravitational lensing, the GWs would also determine the source's luminosity
distance to better than percent accuracy for close sources, degrading to
several percent for more distant sources. Weak lensing cannot, in fact, be
neglected and is expected to limit the accuracy with which distances can be
fixed to errors no less than a few percent. Assuming a well-measured cosmology,
the source's redshift could be inferred with similar accuracy. GWs alone can
thus pinpoint a binary to a three-dimensional ``pixel'' which can help guide
searches for the hosts of these events. We examine the time evolution of this
pixel, studying it at merger and at several intervals before merger. One day
before merger, the major axis of the error ellipse is typically larger than its
final value by a factor of . The minor axis is larger by a factor
of , and, neglecting lensing, the error in the luminosity distance is
larger by a factor of . This large change over a short period of
time is due to spin-induced precession, which is strongest in the final days
before merger. The evolution is slower as we go back further in time. For , we find that GWs will localize a coalescing binary to within $\sim 10\
\mathrm{deg}^2$ as early as a month prior to merger and determine distance (and
hence redshift) to several percent.Comment: 30 pages, 10 figures, 5 tables. Version published in Ap
Pressurised calcination-atmospheric carbonation of limestone for cyclic CO2 capture from flue gases
A study was carried out to investigate the CO2 capture performance of limestone under atmospheric carbonations following pressurised calcination. A series of tests was carried out to study the role of pressurised calcination using a fluidised bed reactor. In this investigation, calcination of limestone particles was carried out at three levels of pressure: 0.1 MPa, 0.5 MPa, and 1.0 MPa. After calcination, the capture performance of the calcined sorbent was tested at atmospheric pressure. As expected, the results indicate that the carbonation conversion of calcined sorbent decreases as the pressure is increased during calcination. Pressurised calcination requires higher temperatures and causes an increase in sorbent sintering, albeit that it would have the advantage of reducing equipment size as well as the compression energy necessary for CO2transport and storage, and an analysis has been provided to give an assessment of the potential benefits associated with such an option using process software.EPSR
Gyroscopes orbiting black holes: A frequency-domain approach to precession and spin-curvature coupling for spinning bodies on generic Kerr orbits
A small body orbiting a black hole follows a trajectory that, at leading order, is a geodesic of the black hole spacetime. Much effort has gone into computing "self-force" corrections to this motion, arising from the small body's own contributions to the system's spacetime. Another correction to the motion arises from coupling of the small body's spin to the black hole's spacetime curvature. Spin-curvature coupling drives a precession of the small body, and introduces a "force" (relative to the geodesic) which shifts the small body's worldline. These effects scale with the small body's spin at leading order. In this paper, we show that the equations which govern spin-curvature coupling can be analyzed with a frequency-domain decomposition, at least to leading order in the small body's spin. We show how to compute the frequency of precession along generic orbits, and how to describe the small body's precession and motion in the frequency domain. We illustrate this approach with a number of examples. This approach is likely to be useful for understanding spin coupling effects in the extreme mass ratio limit, and may provide insight into modeling spin effects in the strong field for nonextreme mass ratios.National Science Foundation (U.S.) (Grant PHY-1403261
Measuring parameters of massive black hole binaries with partially aligned spins
The future space-based gravitational wave detector LISA will be able to
measure parameters of coalescing massive black hole binaries, often to
extremely high accuracy. Previous work has demonstrated that the black hole
spins can have a strong impact on the accuracy of parameter measurement.
Relativistic spin-induced precession modulates the waveform in a manner which
can break degeneracies between parameters, in principle significantly improving
how well they are measured. Recent studies have indicated, however, that spin
precession may be weak for an important subset of astrophysical binary black
holes: those in which the spins are aligned due to interactions with gas. In
this paper, we examine how well a binary's parameters can be measured when its
spins are partially aligned and compare results using waveforms that include
higher post-Newtonian harmonics to those that are truncated at leading
quadrupole order. We find that the weakened precession can substantially
degrade parameter estimation. This degradation is particularly devastating for
the extrinsic parameters sky position and distance. Absent higher harmonics,
LISA typically localizes the sky position of a nearly aligned binary a factor
of less accurately than for one in which the spin orientations are
random. Our knowledge of a source's sky position will thus be worst for the
gas-rich systems which are most likely to produce electromagnetic counterparts.
Fortunately, higher harmonics of the waveform can make up for this degradation.
By including harmonics beyond the quadrupole in our waveform model, we find
that the accuracy with which most of the binary's parameters are measured can
be substantially improved. In some cases, parameters can be measured as well in
partially aligned binaries as they can be when the binary spins are random.Comment: 18 pages, 16 figures, version accepted by PRD (with improved
distributions of partially aligned spins
Correlations in the Far Infrared Background
We compute the expected angular power spectrum of the cosmic Far Infrared
Background (FIRB). We find that the signal due to source correlations dominates
the shot--noise for \ell \la 1000 and results in anisotropies with rms
amplitudes between 5% and 10% of the mean
for l \ga 150. The angular power spectrum depends on several unknown
quantities, such as the UV flux density evolution, optical properties of the
dust, biasing of the sources of the FIRB, and cosmological parameters. However,
when we require our models to reproduce the observed DC level of the FIRB, we
find that the anisotropy is at least a few percent in all cases. This
anisotropy is detectable with proposed instruments, and its measurement will
provide strong constraints on models of galaxy evolution and large-scale
structure at redshifts up to at least .Comment: 7 pages, 4 figures included, uses emulateapj.sty. More models
explored than in original version. Accepted for publication in Ap
Strong-field tidal distortions of rotating black holes: Formalism and results for circular, equatorial orbits
Tidal coupling between members of a compact binary system can have an
interesting and important influence on that binary's dynamical inspiral. Tidal
coupling also distorts the binary's members, changing them (at lowest order)
from spheres to ellipsoids. At least in the limit of fluid bodies and Newtonian
gravity, there are simple connections between the geometry of the distorted
ellipsoid and the impact of tides on the orbit's evolution. In this paper, we
develop tools for investigating tidal distortions of rapidly rotating black
holes using techniques that are good for strong-field, fast-motion binary
orbits. We use black hole perturbation theory, so our results assume extreme
mass ratios. We develop tools to compute the distortion to a black hole's
curvature for any spin parameter, and for tidal fields arising from any bound
orbit, in the frequency domain. We also develop tools to visualize the
horizon's distortion for black hole spin (leaving the more
complicated case to a future analysis). We then study how a
Kerr black hole's event horizon is distorted by a small body in a circular,
equatorial orbit. We find that the connection between the geometry of tidal
distortion and the orbit's evolution is not as simple as in the Newtonian
limit.Comment: 37 pages, 8 figures. Accepted for publication to Physical Review D.
This version corrects a number of typographical errors found when reviewing
the page proof
How black holes get their kicks: Gravitational radiation recoil revisited
Gravitational waves from the coalescence of binary black holes carry away
linear momentum, causing center of mass recoil. This "radiation rocket" effect
has important implications for systems with escape speeds of order the recoil
velocity. We revisit this problem using black hole perturbation theory,
treating the binary as a test mass spiraling into a spinning hole. For extreme
mass ratios (q = m1/m2 << 1) we compute the recoil for the slow inspiral epoch
of binary coalescence very accurately; these results can be extrapolated to q ~
0.4 with modest accuracy. Although the recoil from the final plunge contributes
significantly to the final recoil, we are only able to make crude estimates of
its magnitude. We find that the recoil can easily reach ~ 100-200 km/s, but
most likely does not exceed ~ 500 km/s. Though much lower than previous
estimates, this recoil is large enough to have important astrophysical
consequences. These include the ejection of black holes from globular clusters,
dwarf galaxies, and high-redshift dark matter halos.Comment: 4 pages, 2 figures, emulateapj style; minor changes made; accepted to
ApJ Letter
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