36 research outputs found
Tidal deformations of spinning black holes in Bowen-York initial data
We study the tidal deformations of the shape of a spinning black hole horizon
due to a binary companion in the Bowen-York initial data set. We use the
framework of quasi-local horizons and identify a black hole by marginally outer
trapped surfaces. The intrinsic horizon geometry is specified by a set of mass
and angular-momentum multipole moments and
respectively.
The tidal deformations are described by the change in these multipole moments
caused by an external perturbation. This leads us to define two sets of
dimensionless numbers, the tidal coefficients for and
, which specify the deformations of a black hole with a binary
companion. We compute these tidal coefficients in a specific model problem,
namely the Bowen-York initial data set for binary black holes. We restrict
ourselves to axisymmetric situations and to small spins. Within this
approximation, we analytically compute the conformal factor, the location of
the marginally trapped surfaces, and finally the multipole moments and the
tidal coefficients.Comment: 22 pages, 1 figur
GWSkyNet: A Real-time Classifier for Public Gravitational-wave Candidates
The rapid release of accurate sky localization for gravitational-wave (GW) candidates is crucial for multi-messenger observations. During the third observing run of Advanced LIGO and Advanced Virgo, automated GW alerts were publicly released within minutes of detection. Subsequent inspection and analysis resulted in the eventual retraction of a fraction of the candidates. Updates could be delayed by up to several days, sometimes issued during or after exhaustive multi-messenger follow-up campaigns. We introduce GWSkyNet, a real-time framework to distinguish between astrophysical events and instrumental artifacts using only publicly available information from the LIGO-Virgo open public alerts. This framework consists of a non-sequential convolutional neural network involving sky maps and metadata. GWSkyNet achieves a prediction accuracy of 93.5% on a testing data set
Low significance of evidence for black hole echoes in gravitational wave data
Recent detections of merging black holes allow observational tests of the
nature of these objects. In some proposed models, non-trivial structure at or
near the black hole horizon could lead to echo signals in gravitational wave
data. Recently, Abedi et al. claimed tentative evidence for repeating damped
echo signals following the gravitational-wave signals of the binary black hole
merger events recorded in the first observational period of the Advanced LIGO
interferometers. We reanalyse the same data, addressing some of the
shortcomings of their method using more background data and a modified
procedure. We find a reduced statistical significance for the claims of
evidence for echoes, calculating increased p-values for the null hypothesis of
echo-free noise. The reduced significance is entirely consistent with noise,
and so we conclude that the analysis of Abedi et al. does not provide any
observational evidence for the existence of Planck-scale structure at black
hole horizons.Comment: As accepted by Physical Review
Blip glitches in Advanced LIGO data
Blip glitches are short noise transients present in data from ground-based
gravitational-wave observatories. These glitches resemble the
gravitational-wave signature of massive binary black hole mergers. Hence, the
sensitivity of transient gravitational-wave searches to such high-mass systems
and other potential short duration sources is degraded by the presence of blip
glitches. The origin and rate of occurrence of this type of glitch have been
largely unknown. In this paper we explore the population of blip glitches in
Advanced LIGO during its first and second observing runs. On average, we find
that Advanced LIGO data contains approximately two blip glitches per hour of
data. We identify four subsets of blip glitches correlated with detector
auxiliary or environmental sensor channels, however the physical causes of the
majority of blips remain unclear
Gravity Spy: Integrating Advanced LIGO Detector Characterization, Machine Learning, and Citizen Science
(abridged for arXiv) With the first direct detection of gravitational waves,
the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) has
initiated a new field of astronomy by providing an alternate means of sensing
the universe. The extreme sensitivity required to make such detections is
achieved through exquisite isolation of all sensitive components of LIGO from
non-gravitational-wave disturbances. Nonetheless, LIGO is still susceptible to
a variety of instrumental and environmental sources of noise that contaminate
the data. Of particular concern are noise features known as glitches, which are
transient and non-Gaussian in their nature, and occur at a high enough rate so
that accidental coincidence between the two LIGO detectors is non-negligible.
In this paper we describe an innovative project that combines crowdsourcing
with machine learning to aid in the challenging task of categorizing all of the
glitches recorded by the LIGO detectors. Through the Zooniverse platform, we
engage and recruit volunteers from the public to categorize images of glitches
into pre-identified morphological classes and to discover new classes that
appear as the detectors evolve. In addition, machine learning algorithms are
used to categorize images after being trained on human-classified examples of
the morphological classes. Leveraging the strengths of both classification
methods, we create a combined method with the aim of improving the efficiency
and accuracy of each individual classifier. The resulting classification and
characterization should help LIGO scientists to identify causes of glitches and
subsequently eliminate them from the data or the detector entirely, thereby
improving the rate and accuracy of gravitational-wave observations. We
demonstrate these methods using a small subset of data from LIGO's first
observing run.Comment: 27 pages, 8 figures, 1 tabl
Statistical validation of the detection of a sub-dominant quasi-normal mode in GW190521
One of the major aims of gravitational wave astronomy is to observationally
test the Kerr nature of black holes. The strongest such test, with minimal
additional assumptions, is provided by observations of multiple ringdown modes,
also known as black hole spectroscopy. For the gravitational wave merger event
GW190521, we have previously claimed the detection of two ringdown modes
emitted by the remnant black hole. In this paper we provide further evidence
for the detection of multiple ringdown modes from this event. We analyse the
recovery of simulated gravitational wave signals designed to replicate the
ringdown properties of GW190521. We quantify how often our detection statistic
reports strong evidence for a sub-dominant ringdown mode,
even when no such mode is present in the simulated signal. We find this only
occurs with a probability , which is consistent with a Bayes factor
of (1 uncertainty) found for GW190521. We also quantify our
agnostic analysis of GW190521, in which no relationship is assumed between
ringdown modes, and find that only 1 in 250 simulated signals without a
mode yields a result as significant as GW190521. Conversely, we
verify that when simulated signals do have an observable mode they
consistently yield a strong evidence and significant agnostic results. We also
find that constraints on deviations from the mode on GW190521-like
signals with a mode are consistent with what was obtained from our
previous analysis of GW190521. Our results strongly support our previous
conclusion that the gravitational wave signal from GW190521 contains an
observable sub-dominant mode.Comment: 16 pages, 10 figure
A multimode quasi-normal spectrum from a perturbed black hole
When two black holes merge, the late stage of gravitational wave emission is
a superposition of exponentially damped sinusoids. According to the black hole
no-hair theorem, this ringdown spectrum depends only on the mass and angular
momentum of the final black hole. An observation of more than one ringdown mode
can test this fundamental prediction of general relativity. Here we provide
strong observational evidence for a multimode black hole ringdown spectrum
using the gravitational wave event GW190521, with a maximum Bayes factor of
( uncertainty) preferring two fundamental modes over one. The
dominant mode is the harmonic, and the sub-dominant mode corresponds
to the harmonic. The amplitude of this mode relative to the dominant
harmonic is estimated to be . We estimate
the redshifted mass and dimensionless spin of the final black hole as
and , respectively.
We find that the final black hole is consistent with the no hair theorem and
constrain the fractional deviation from general relativity of the sub-dominant
mode's frequency to be .Comment: Accepted for publication in PRL. 7 pages, 4 figures, plus
supplemental. Data available at
https://github.com/gwastro/BH-Spectroscopy-GW19052