618 research outputs found
Myths of a Near Past: Envisioning Finance Capitalism anno 2007
This paper seeks to extend earlier work on particular features and manifestations of capitalism (De Cock et al., 2001). Our 2001 Myths of a Near Future paper offered ephemera readers a large depository of images concerning the New Economy. Eight years later our focus has shifted to Finance Capitalism. Over the course of the year 2007 we cut out and scanned 81 ads placed by financial institutions in the Financial Times. Our analysis of these aims to provide a sense of how the financial world ?showed up? in this pivotal year, whilst illustrating how its representations were interwoven with fantasy throughout. We also hope that the ensemble of images associated with the paper will be creatively reassembled by its readers and possibly provide a useful teaching aid
The effect of gravitational-wave recoil on the demography of massive black holes
The coalescence of massive black hole (MBH) binaries following galaxy mergers
is one of the main sources of low-frequency gravitational radiation. A
higher-order relativistic phenomenon, the recoil as a result of the non-zero
net linear momentum carried away by gravitational waves, may have interesting
consequences for the demography of MBHs at the centers of galaxies. We study
the dynamics of recoiling MBHs and its observational consequences. The
``gravitational rocket'' may: i) deplete MBHs from late-type spirals, dwarf
galaxies, and stellar clusters; ii) produce off-nuclear quasars, including
unusual radio morphologies during the recoil of a radio-loud source; and iii)
give rise to a population of interstellar and intergalactic MBHs.Comment: emulateapj, 5 pages, 2 figures, to appear in the ApJ Letter
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
The Assembly and Merging History of Supermassive Black Holes in Hierarchical Models of Galaxy Formation
We assess models for the assembly of supermassive black holes (SMBHs) at the
center of galaxies that trace their hierarchical build-up far up in the dark
halo `merger tree'. We assume that the first `seed' black holes (BHs) formed in
(mini)halos collapsing at z=20 from high-sigma density fluctuations. As these
pregalactic holes become incorporated through a series of mergers into larger
and larger halos, they sink to the center owing to dynamical friction, accrete
a fraction of the gas in the merger remnant to become supermassive, form a
binary system, and eventually coalesce. The merger history of dark matter halos
and associated BHs is followed by cosmological Monte Carlo realizations of the
merger hierarchy. A simple model, where quasar activity is driven by major
mergers and SMBHs accrete at the Eddington rate a mass that scales with the
fifth power of the velocity dispersion, is shown to reproduce the optical LF of
quasars in the redshift range 1<z<4. Binary and triple BH interactions are
followed in our merger tree. The assumptions underlying our scenario lead to
the prediction of a population of massive BHs wandering in galaxy halos and the
intergalactic medium at the present epoch, and contributing <10% to the total
BH mass density. At all epochs the fraction of binary SMBHs in galaxy nuclei is
of order 10%, while the fraction of binary quasars is less than 0.3%Comment: revised version, accepted for publication in the ApJ, emulateapj, 15
pages, 16 figure
Recoil velocity at 2PN order for spinning black hole binaries
We compute the flux of linear momentum carried by gravitational waves emitted
from spinning binary black holes at 2PN order for generic orbits. In particular
we provide explicit expressions of three new types of terms, namely
next-to-leading order spin-orbit terms at 1.5 PN order, spin-orbit tail terms
at 2PN order, and spin-spin terms at 2PN order. Restricting ourselves to
quasi-circular orbits, we integrate the linear momentum flux over time to
obtain the recoil velocity as function of orbital frequency. We find that in
the so-called superkick configuration the higher-order spin corrections can
increase the recoil velocity up to about a factor 3 with respect to the
leading-order PN prediction. Furthermore, we provide expressions valid for
generic orbits, and accurate at 2PN order, for the energy and angular momentum
carried by gravitational waves emitted from spinning binary black holes.
Specializing to quasi-circular orbits we compute the spin-spin terms at 2PN
order in the expression for the evolution of the orbital frequency and found
agreement with Mik\'oczi, Vas\'uth and Gergely. We also verified that in the
limit of extreme mass ratio our expressions for the energy and angular momentum
fluxes match the ones of Tagoshi, Shibata, Tanaka and Sasaki obtained in the
context of black hole perturbation theory.Comment: 28 pages (PRD format), 1 figure, reference added, version published
in PRD, except that the PRD version contains a sign error: the sign of the
RHS of Eqs.(4.26) and (4.27) is wrong; it has been corrected in this
replacemen
Four-Body Effects in Globular Cluster Black Hole Coalescence
In the high density cores of globular clusters, multibody interactions are
expected to be common, with the result that black holes in binaries are
hardened by interactions. It was shown by Sigurdsson & Hernquist (1993) and
others that 10 solar mass black holes interacting exclusively by three-body
encounters do not merge in the clusters themselves, because recoil kicks the
binaries out of the clusters before the binaries are tight enough to merge.
Here we consider a new mechanism, involving four-body encounters. Numerical
simulations by a number of authors suggest that roughly 20-50% of binary-binary
encounters will eject one star but leave behind a stable hierarchical triple.
If the orbital plane of the inner binary is strongly tilted with respect to the
orbital plane of the outer object, a secular Kozai resonance, first
investigated in the context of asteroids in the Solar System, can increase the
eccentricity of the inner body significantly. We show that in a substantial
fraction of cases the eccentricity is driven to a high enough value that the
inner binary will merge by gravitational radiation, without a strong
accompanying kick. Thus the merged object remains in the cluster; depending on
the binary fraction of black holes and the inclination distribution of
newly-formed hierarchical triples, this mechanism may allow massive black holes
to accumulate through successive mergers in the cores of globular clusters. It
may also increase the likelihood that stellar-mass black holes in globular
clusters will be detectable by their gravitational radiation.Comment: Submitted to ApJ Letters (includes emulateapj.sty
Rates and Characteristics of Intermediate Mass Ratio Inspirals Detectable by Advanced LIGO
Gravitational waves (GWs) from the inspiral of a neutron star (NS) or
stellar-mass black hole (BH) into an intermediate-mass black hole (IMBH) with
mass between ~50 and ~350 solar masses may be detectable by the planned
advanced generation of ground-based GW interferometers. Such intermediate mass
ratio inspirals (IMRIs) are most likely to be found in globular clusters. We
analyze four possible IMRI formation mechanisms: (1) hardening of an NS-IMBH or
BH-IMBH binary via three-body interactions, (2) hardening via Kozai resonance
in a hierarchical triple system, (3) direct capture, and (4) inspiral of a
compact object from a tidally captured main-sequence star; we also discuss
tidal effects when the inspiraling object is an NS. For each mechanism we
predict the typical eccentricities of the resulting IMRIs. We find that IMRIs
will have largely circularized by the time they enter the sensitivity band of
ground-based detectors. Hardening of a binary via three-body interactions,
which is likely to be the dominant mechanism for IMRI formation, yields
eccentricities under 10^-4 when the GW frequency reaches 10 Hz. Even among
IMRIs formed via direct captures, which can have the highest eccentricities,
around 90% will circularize to eccentricities under 0.1 before the GW frequency
reaches 10 Hz. We estimate the rate of IMRI coalescences in globular clusters
and the sensitivity of a network of three Advanced LIGO detectors to the
resulting GWs. We show that this detector network may see up to tens of IMRIs
per year, although rates of one to a few per year may be more plausible. We
also estimate the loss in signal-to-noise ratio that will result from using
circular IMRI templates for data analysis and find that, for the eccentricities
we expect, this loss is negligible.Comment: Accepted for publication in ApJ; revised version reflects changes
made to the article during the acceptance proces
Gravitational Radiation from Intermediate-Mass Black Holes
Recent X-ray observations of galaxies with ROSAT, ASCA, and Chandra have
revealed numerous bright off-center point sources which, if isotropic emitters,
are likely to be intermediate-mass black holes, with hundreds to thousands of
solar masses. The origin of these objects is under debate, but observations
suggest that a significant number of them currently reside in young
high-density stellar clusters. There is also growing evidence that some
Galactic globular clusters harbor black holes of similar mass, from
observations of stellar kinematics. In such high-density stellar environments,
the interactions of intermediate-mass black holes are promising sources of
gravitational waves for ground-based and space-based detectors. Here we explore
the signal strengths of binaries containing intermediate-mass black holes or
stellar-mass black holes in dense stellar clusters. We estimate that a few to
tens per year of these objects will be detectable during the last phase of
their inspiral with the advanced LIGO detector, and up to tens per year will be
seen during merger, depending on the spins of the black holes. We also find
that if these objects reside in globular clusters then tens of sources will be
detectable with LISA from the Galactic globular system in a five year
integration, and similar numbers will be detectable from more distant galaxies.
The signal strength depends on the eccentricity distribution, but we show that
there is promise for strong detection of pericenter precession and
Lense-Thirring precession of the orbital plane. We conclude by discussing what
could be learned about binaries, dense stellar systems, and strong gravity if
such signals are detected.Comment: Minor changes, accepted by ApJ (December 10, 2002
Perturbative effects of spinning black holes with applications to recoil velocities
Recently, we proposed an enhancement of the Regge-Wheeler-Zerilli formalism
for first-order perturbations about a Schwarzschild background that includes
first-order corrections due to the background black-hole spin. Using this
formalism, we investigate gravitational wave recoil effects from a spinning
black-hole binary system analytically. This allows us to better understand the
origin of the large recoils observed in full numerical simulation of spinning
black hole binaries.Comment: Proceedings of Theory Meets Data Analysis at Comparable and Extreme
Mass Ratios (NRDA/Capra 2010), Perimeter Institute, June 2010 - 12 page
Quasars at z=6: the survival of the fittest
The Sloan Digital Sky survey detected luminous quasars at very high redshift,
z>6. Follow-up observations indicated that at least some of these quasars are
powered by supermassive black holes (SMBHs) with masses in excess of billion
solar masses. SMBHs, therefore, seem to have already existed when the Universe
was less than 1 Gyr old, and the bulk of galaxy formation still has to take
place. We investigate in this paper to which extent accretion and dynamical
processes influence the early growth of SMBHs. We assess the impact of (i)
black hole mergers, (ii) the influence of the merging efficiency and (iii) the
negative contribution due to dynamical effects which can kick black holes out
of their host halos (gravitational recoil). We find that if accretion is always
limited by the Eddington rate via a thin disc, the maximum radiative efficiency
allowed to reproduce the LF at z=6 is of order 12%, when the adverse effect of
the gravitational recoil is taken into consideration. Dynamical effects cannot
be neglected in studies of high-redshift SMBHs. If black holes can accrete at
super-critical rate during an early phase, reproducing the observed SMBH mass
values is not an issue, even in the case that the recoil velocity is in the
upper limits range, as the mass ratios of merging binaries are skewed towards
low values, where the gravitational recoil effect is very mild. We propose that
SMBH growth at early times is very selective, and efficient only for black
holes hosted in high density peak halos.Comment: Accepted for publication in the ApJ. 9 pages, 6 b/w figure
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