1,637 research outputs found
White dwarfs stripped by massive black holes: sources of coincident gravitational and electromagnetic radiation
White dwarfs inspiraling into black holes of mass \MBH\simgt 10^5M_\odot
are detectable sources of gravitational waves in the LISA band. In many of
these events, the white dwarf begins to lose mass during the main observational
phase of the inspiral. The mass loss starts gently and can last for thousands
of orbits. The white dwarf matter overflows the Roche lobe through the
point at each pericenter passage and the mass loss repeats periodically. The
process occurs very close to the black hole and the released gas can accrete,
creating a bright source of radiation with luminosity close to the Eddington
limit, ~erg~s. This class of inspirals offers a promising
scenario for dual detections of gravitational waves and electromagnetic
radiation.Comment: 5 pages, 3 figures. Minor changes. Accepted in MNRAS Letters on
August 6 201
Extreme mass ratio inspiral rates: dependence on the massive black hole mass
We study the rate at which stars spiral into a massive black hole (MBH) due
to the emission of gravitational waves (GWs), as a function of the mass M of
the MBH. In the context of our model, it is shown analytically that the rate
approximately depends on the MBH mass as M^{-1/4}. Numerical simulations
confirm this result, and show that for all MBH masses, the event rate is
highest for stellar black holes, followed by white dwarfs, and lowest for
neutron stars. The Laser Interferometer Space Antenna (LISA) is expected to see
hundreds of these extreme mass ratio inspirals per year. Since the event rate
derived here formally diverges as M->0, the model presented here cannot hold
for MBHs of masses that are too low, and we discuss what the limitations of the
model are.Comment: Accepted to CQG, special LISA issu
The impact of realistic models of mass segregation on the event rate of extreme-mass ratio inspirals and cusp re-growth
One of the most interesting sources of gravitational waves (GWs) for LISA is
the inspiral of compact objects on to a massive black hole (MBH), commonly
referred to as an "extreme-mass ratio inspiral" (EMRI). The small object,
typically a stellar black hole (bh), emits significant amounts of GW along each
orbit in the detector bandwidth. The slowly, adiabatic inspiral of these
sources will allow us to map space-time around MBHs in detail, as well as to
test our current conception of gravitation in the strong regime. The event rate
of this kind of source has been addressed many times in the literature and the
numbers reported fluctuate by orders of magnitude. On the other hand, recent
observations of the Galactic center revealed a dearth of giant stars inside the
inner parsec relative to the numbers theoretically expected for a fully relaxed
stellar cusp. The possibility of unrelaxed nuclei (or, equivalently, with no or
only a very shallow cusp) adds substantial uncertainty to the estimates. Having
this timely question in mind, we run a significant number of direct-summation
body simulations with up to half a million particles to calibrate a much
faster orbit-averaged Fokker-Planck code. We then investigate the regime of
strong mass segregation (SMS) for models with two different stellar mass
components. We show that, under quite generic initial conditions, the time
required for the growth of a relaxed, mass segregated stellar cusp is shorter
than a Hubble time for MBHs with
(i.e. nuclei in the range of LISA). SMS has a significant impact boosting the
EMRI rates by a factor of for our fiducial models of Milky Way type
galactic nuclei.Comment: Accepted by CQG, minor changes, a bit expande
Towards adiabatic waveforms for inspiral into Kerr black holes: I. A new model of the source for the time domain perturbation equation
We revisit the problem of the emission of gravitational waves from a test
mass orbiting and thus perturbing a Kerr black hole. The source term of the
Teukolsky perturbation equation contains a Dirac delta function which
represents a point particle. We present a technique to effectively model the
delta function and its derivatives using as few as four points on a numerical
grid. The source term is then incorporated into a code that evolves the
Teukolsky equation in the time domain as a (2+1) dimensional PDE. The waveforms
and energy fluxes are extracted far from the black hole. Our comparisons with
earlier work show an order of magnitude gain in performance (speed) and
numerical errors less than 1% for a large fraction of parameter space. As a
first application of this code, we analyze the effect of finite extraction
radius on the energy fluxes. This paper is the first in a series whose goal is
to develop adiabatic waveforms describing the inspiral of a small compact body
into a massive Kerr black hole.Comment: 21 pages, 6 figures, accepted by PRD. This version removes the
appendix; that content will be subsumed into future wor
On the tidal evolution of the orbits of low-mass satellites around black holes
Low-mass satellites, like asteroids and comets, are expected to be present
around the black hole at the Galactic center. We consider small bodies orbiting
a black hole, and we study the evolution of their orbits due to tidal
interaction with the black hole. In this paper we investigate the consequences
of the existence of plunging orbits when a black hole is present. We are
interested in finding the conditions that exist when capture occurs. The main
difference between the Keplerian and black hole cases is in the existence of
plunging orbits. Orbital evolution, leading from bound to plunging orbits, goes
through a final unstable circular orbit. On this orbit, tidal energy is
released on a characteristic black hole timescale. This process may be relevant
for explaining how small, compact clumps of material can be brought onto
plunging orbits, where they may produce individual short duration accretion
events. The available energy and the characteristic timescale are consistent
with energy released and the timescale typical of Galactic flares.Comment: 7 pages, 6 figure
Clostridium difficile in a farrowing pen
Clostridium difficile is an important cause of enteric disease in humans. In pigs Clostridium difficile can cause neonatal enteritis and can be isolated from faeces from diseased and healthy animals. According to recent research, isolates from humans and animals show genetic and phenotypic overlap. In The Netherlands, strains isolated from diseased piglets were indistinguishable from strains isolated from Dutch patients. These strains belonged to ribotype 078. Because pigs can either be clinical hosts and/or may be a possible reservoir more understanding of the epidemiology of Clostridium difficile among pigs is needed. The objectives of this study were to specify whether, how and when newborn piglets get infected by Clostridium difficile for the first time. With this intention, six sows, their farrowing crates and litters (71 piglets) at one farm were sampled around the day of birth of the piglets. Within 48 hours after birth, all sampled 71 piglets at the farm became positive for Clostridium difficile ribotype 078. Moreover, all sows became positive within 113 hours after birth of the piglets and the farrowing crates were intermittently positive during the sampling period. This research shows that the sow, the farrowing crate, the air and the teats of the sow are possible transmission routes of Clostridium difficile ribotype 078.This information might help to advise farmers on taking measures against Clostridium difficile infections in neonatal piglets
Affect dysregulation, psychoform dissociation, and adult relational fears mediate the relationship between childhood trauma and complex posttraumatic stress disorder independent of the symptoms of borderline personality disorder
Objective: Complex posttraumatic stress disorder (CPTSD) as defined by the Disorders of Extreme Stress Not Otherwise Specified (DESNOS) formulation is associated with childhood relational trauma and involves relational impairment, affect dysregulation, and identity alterations. However, the distinct contributions of relational impairment (operationalized in the form fears of closeness or abandonment), affect dysregulation (operationalized in the form of overregulation and under-regulation of affect), and identity alterations (operationalized in the form of positive or negative psychoform or somatoform dissociation) to the relationship between childhood trauma and CPTSD/DESNOS have not been systematically tested. Method and Results: In a clinical sample of adults diagnosed with severe and chronic psychiatric and personality disorders (n = 472; M = 34.7 years, SD = 10.1), structural equation modelling with bootstrap 95% confidence intervals demonstrated that the association between childhood trauma and CPTSD/DESNOS symptoms in adulthood was partially mediated by under-regulation of aff
The origin of variability of the intermediate-mass black-hole ULX system HLX-1 in ESO 243-49
The ultra-luminous intermediate-mass black-hole system HLX-1 in the ESO
243-49 galaxy exhibits variability with a possible recurrence time of a few
hundred days. Finding the origin of this variability would constrain the still
largely unknown properties of this extraordinary object. Since it exhibits an
intensity-hardness behavior characteristic of black-hole X-ray transients, we
have analyzed the variability of HLX-1 in the framework of the disk instability
model that explains outbursts of such systems. We find that the long-term
variability of HLX-1 is unlikely to be explained by a model in which outbursts
are triggered by thermal-viscous instabilities in an accretion disc. Possible
alternatives include the instability in a radiation-pressure dominated disk but
we argue that a more likely explanation is a modulated mass-transfer due to
tidal stripping of a star on an eccentric orbit around the intermediate-mass
black hole. We consider an evolutionary scenario leading to the creation of
such a system and estimate the probability of its observation. We conclude,
using a simplified dynamical model of the post-collapse cluster, that no more
than 1/100 to 1/10 of Mbh < 10^4 Msun IMBHs - formed by run-away stellar
mergers in the dense collapsed cores of young clusters - could have a few times
1 Msun Main-Sequence star evolve to an AGB on an orbit eccentric enough for
mass transfer at periapse, while avoiding collisional destruction or being
scattered into the IMBH by 2-body encounters. The finite but low probability of
this configuration is consistent with the uniqueness of HLX-1. We note,
however, that the actual response of a standard accretion disk to bursts of
mass transfer may be too slow to explain the observations unless the orbit is
close to parabolic (and hence even rarer) and/or additional heating, presumably
linked to the highly time-dependent gravitational potential, are invoked.Comment: 8 pages, 2 figures. Additional figure, extended discussion. To be
published in ApJ, June 10, 2011, v734 -
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