950 research outputs found
Verifying the no-hair property of massive compact objects with intermediate-mass-ratio inspirals in advanced gravitational-wave detectors
The detection of gravitational waves from the inspiral of a neutron star or
stellar-mass black hole into an intermediate-mass black hole (IMBH) promises an
entirely new look at strong-field gravitational physics. Gravitational waves
from these intermediate-mass-ratio inspirals (IMRIs), systems with mass ratios
from ~10:1 to ~100:1, may be detectable at rates of up to a few tens per year
by Advanced LIGO/Virgo and will encode a signature of the central body's
spacetime. Direct observation of the spacetime will allow us to use the
"no-hair" theorem of general relativity to determine if the IMBH is a Kerr
black hole (or some more exotic object, e.g. a boson star). Using modified
post-Newtonian (pN) waveforms, we explore the prospects for constraining the
central body's mass-quadrupole moment in the advanced-detector era. We use the
Fisher information matrix to estimate the accuracy with which the parameters of
the central body can be measured. We find that for favorable mass and spin
combinations, the quadrupole moment of a non-Kerr central body can be measured
to within a ~15% fractional error or better using 3.5 pN order waveforms; on
the other hand, we find the accuracy decreases to ~100% fractional error using
2 pN waveforms, except for a narrow band of values of the best-fit non-Kerr
quadrupole moment.Comment: Second version, 12 pages, 5 figures, accepted by PR
Binary Black Holes in Dense Star Clusters: Exploring the Theoretical Uncertainties
Recent N-body simulations predict that large numbers of stellar black holes
(BHs) could remain bound to globular clusters (GCs) at present, and merging
BH--BH binaries are produced dynamically in significant numbers. We
systematically vary "standard" assumptions made by numerical simulations
related to, e.g., BH formation, stellar winds, binary properties of high-mass
stars, and IMF within existing uncertainties, and study the effects on the
evolution of the structural properties of GCs, and the BHs in GCs. We find that
variations in initial assumptions can set otherwise identical initial clusters
on completely different evolutionary paths, significantly affecting their
present observable properties, or even affecting the cluster's very survival to
the present. However, these changes usually do not affect the numbers or
properties of local BH--BH mergers. The only exception is that variations in
the assumed winds and IMF can change the masses and numbers of local BH--BH
mergers, respectively. All other variations (e.g., in initial binary properties
and binary fraction) leave the masses and numbers of locally merging BH--BH
binaries largely unchanged. This is in contrast to binary population synthesis
models for the field, where results are very sensitive to many uncertain
parameters in the initial binary properties and binary stellar-evolution
physics. We find that weak winds are required for producing GW150914-like
mergers from GCs at low redshifts. LVT151012 can be produced in GCs modeled
both with strong and weak winds. GW151226 is lower-mass than typical mergers
from GCs modeled with weak winds, but is similar to mergers from GCs modeled
with strong winds.Comment: 25 pages, 20 figures, 4 tables, ApJ in pres
Measuring the star formation rate with gravitational waves from binary black holes
A measurement of the history of cosmic star formation is central to
understand the origin and evolution of galaxies. The measurement is extremely
challenging using electromagnetic radiation: significant modeling is required
to convert luminosity to mass, and to properly account for dust attenuation,
for example. Here we show how detections of gravitational waves from
inspiraling binary black holes made by proposed third-generation detectors can
be used to measure the star formation rate of massive stars with high precision
up to redshifts of ~10. Depending on the time-delay model, the predicted
detection rates ranges from ~1400 to ~16000 per month with the current
measurement of local merger rate density. With three months of observations,
parameters describing the volumetric star formation rate can be constrained at
the few percent level, and the volumetric merger rate can be directly measured
to 3% at z~2. Given a parameterized star formation rate, the characteristic
delay time between binary formation and merger can be measured to ~60%.Comment: 7 pages, 1 table, 4 fig
Post-Newtonian Dynamics in Dense Star Clusters: Highly-Eccentric, Highly-Spinning, and Repeated Binary Black Hole Mergers
We present models of realistic globular clusters with post-Newtonian dynamics
for black holes. By modeling the relativistic accelerations and
gravitational-wave emission in isolated binaries and during three- and
four-body encounters, we find that nearly half of all binary black hole mergers
occur inside the cluster, with about 10% of those mergers entering the
LIGO/Virgo band with eccentricities greater than 0.1. In-cluster mergers lead
to the birth of a second generation of black holes with larger masses and high
spins, which, depending on the black hole natal spins, can sometimes be
retained in the cluster and merge again. As a result, globular clusters can
produce merging binaries with detectable spins regardless of the birth spins of
black holes formed from massive stars. These second-generation black holes
would also populate any upper mass gap created by pair-instability supernovae.Comment: 9 pages, 3 figures, 2 appendices. To appear in Physical Review
Letter
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