13 research outputs found
Observational tests of fundamental physics from gravitational wave detections
With the detection of the signal GW150914 from the collision of two black holes in 2015,
observational gravitational wave physics has begun. Many more signals have since been recorded,
and new detections are now becoming routine. These observations offer a new window to probe
fundamental physics in thus far inaccessible regimes of strong gravity, such as in the regions near
black hole horizons. The work presented here pursues this through two approaches, studying
predicted signals of either black holes of general relativity, or of proposed alternative objects
without horizons.
A binary black hole collision creates a single perturbed black hole, which settles to its final
state through the ringdown gravitational wave emission. The ringdown consists of a spectrum
of modes, which the no-hair theorem in General Relativity predicts to be determined entirely
by the black hole mass and angular momentum. Measurement of multiple modes allows to test
this prediction but is challenging due to the weak and short-lived nature of the ringdown signal.
Two studies are presented on the feasibility of such tests using current and near-future de-
tector sensitivities. Large populations of simulated ringdown signals are constructed based on
observational models of the binary black hole population. Bayesian parameter estimation techniques are applied to these signals to place bounds on deviations from the no-hair prediction.
Detections leading to stringent bounds are unlikely to occur for current instruments but can
be found during a few years of operation at their planned future sensitivities. The prospects
improve when extending the analysis to combine data from multiple detections into a single
bound on deviations. At the sensitivity planned for the next observation run of current instruments, the detections from one year of data can be combined into stringent bounds. Solutions
are provided to limitations uncovered for this type of study.
In a further study, strong evidence is found for the presence of a subdominant mode in
the data of the event GW190521. A new method is employed to allow the analysis of only
the ringdown part of the signal, without contamination from outside the analysis window and
preventing windowing artefacts and signal loss. Tests of the no-hair theorem are performed,
yielding unexpectedly tight constraints on deviations.
Two phenomenologically distinct signals from horizonless compact objects are studied, both
following after the primary signal which is otherwise unchanged compared to that of a black
hole binary. One takes the form of repeated pulses after the ringdown, called gravitational wave
echoes, while the other consists of a very long-lived damped sinusoid with a small amplitude.
Using a simplified waveform model for echoes, evidence for such signals in the data of several
detections is evaluated. Previous results from the first search for these are replicated, and the
methods tested thoroughly. Through improved estimation methods, low statistical significance
is established for these results, yet the presence of such signals cannot be ruled out by the
analysis. An independent Bayesian analysis is performed for the same waveform model, with
results for each event either preferring the absence of echoes in the data or being consistent with
it. Bounds on the echo amplitudes ruled out by the data are produced.
The long-lived mode signal for a broad class of horizonless objects is considered in a Bayesian
analysis. Methods are developed to accommodate the long duration of the signal, and their
performance is tested with simulated signals and off-source data. They are then applied to
the data of the event GW150914, yielding stringent bounds on the deviations from the Kerr
geometry exhibited by such objects.Mit der Detektion des Signals GW150914 von der Kollision zweier schwarzer Löcher im Jahr
2015 begann die beobachtungsbasierte Gravitationswellenphysik. Viele weitere Signale wurden
seither aufgezeichnet und neue Detektionen werden zur Routine. Diese Beobachtungen eröffnen
einen neuen Weg, fundamentale Physik im bisher unzugÀnglichen Regime starker Gravitation zu untersuchen, zum Beispiel in der Umgebung der Horizonte schwarzer Löcher. Die hier
prÀsentierten Studien verfolgen dies durch zwei AnsÀtze, indem sie entweder die vorhergesagten
Signale schwarzer Löcher in der Allgemeinen RelativitÀtstheorie oder vorgeschlagener alternativer Objekte ohne Horizonte untersuchen.
Die Kollision zweier schwarzer Löcher erzeugt ein einzelnes gestörtes schwarzes Loch, welches durch Emission der Abkling-Gravitationswellen schlieĂlich in einen ungestörten Zustand
ĂŒbergeht. Die Abkling-Strahlung besteht aus einem Spektrum von Moden, welche dem Keine-
Haare-Theorem der Allgemeinen RelativitÀtstheorie nach gÀnzlich durch Masse und Drehimpuls
des schwarzen Loches bestimmt werden. Die Messung mehrerer Moden ermöglicht die PrĂŒfung
dieser Vorhersage, ist jedoch wegen des schwachen und kurzlebigen Abklingsignals schwierig.
Zwei Studien zur DurchfĂŒhrbarkeit solcher Tests mithilfe aktuell und in naher Zukunft verfĂŒgbarer Detektor-Empfindlichkeiten werden dargelegt. GroĂe Populationen simulierter Abklingsignale werden konstruiert, basierend auf beobachtungsgestĂŒtzten Modellen der Population von
BinÀrsystemen schwarzer Löcher. Bayessche ParameterabschÀtzung wird auf diese Signale angewendet, um Abweichungen von der Keine-Haare-Vorhersage zu beschrÀnken. Detektionen, die
zu strikter Begrenzung fĂŒhren, sind mit aktuellen Instrumenten unwahrscheinlich, können aber
innerhalb weniger Jahre des Betriebs mit ihren geplanten zukĂŒnftigen Empfindlichkeiten erreicht
werden. Diese Aussichten verbessern sich, wenn Daten mehrerer Detektionen in der Begrenzung
kombiniert werden. Mit der geplanten Empfindlichkeit aktueller Instrumente im nÀchsten Beobachtungslauf können die in einem Jahr gesammelten Daten zu strikten Begrenzungen kombiniert
werden. Lösungen fĂŒr die entdeckten Limitationen dieser Art Analyse werden vorgestellt.
In einer weiteren Studie wird starke Evidenz fĂŒr die Existenz einer subdominanten Mode
in den Daten des Signals GW190521 gefunden. Eine neue Methode wird eingesetzt, welche
die Analyse des Abkling-Signals ermöglicht, ohne Kontamination von auĂerhalb des Analyse-
Fensters, Artefakte oder Signalverlust zu verursachen. Tests des Keine-Haare-Theorems werden
durchgefĂŒhrt und liefern unerwartet strikte BeschrĂ€nkungen fĂŒr Abweichungen.
Zwei phĂ€nomenologisch verschiedene Signale horizontfreier kompakter Objekte werden untersucht. Beide folgen dem PrimĂ€rsignal, das ansonsten gegenĂŒber dem schwarzer Löcher un-
verÀndert ist. Eines besteht aus wiederholten Pulsen, als Gravitationswellen-Echos bezeichnet,
wÀhrend das zweite die Form einer langlebigen, gedÀmpften Sinuswelle geringer Amplitude hat.
Anhand eines vereinfachten Modells der Echo-Wellenform wird die Evidenz solcher Signale in
den Daten mehrerer Detektionen bewertet. FrĂŒhere Ergebnisse der ersten Suche nach Echos werden repliziert und die Methoden ausfĂŒhrlich geprĂŒft. Durch verbesserte AbschĂ€tzungsmethoden
wird eine geringe statistische Signifikanz der Ergebnisse etabliert, allerdings kann die Anwesenheit solcher Signale nicht durch diese Untersuchung ausgeschlossen werden. Eine unabhÀngige
Bayessche Analyse wird mit derselben Wellenform durchgefĂŒhrt, wobei die Ergebnisse die Abwesenheit des Signals bevorzugen oder mit Rauschen vereinbar sind. Grenzen fĂŒr die von den
Daten ausgeschlossenen Amplituden der Echos werden gefunden.
Das Signal einer langlebigen Mode von einer groĂen Klasse horizontfreier Objekte wird in
einer Bayesschen Analyse betrachtet. Methoden werden entwickelt, um die lange Dauer des
Signals handhaben zu können, und ihre LeistungsfÀhigkeit wird an simulierten Signalen und
signalfreien Daten getestet. Auf die Daten des Signals GW150914 angewendet, liefern sie strikte
BeschrĂ€nkungen fĂŒr die Abweichungen solcher Objekte von der Kerr-Geometrie
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
A frequency-domain perspective on GW150914 ringdown overtone
We revisit the recent debate on the evidence for an overtone in the black
hole ringdown of GW150914. By gating and inpainting the data, we discard the
contamination from earlier parts of the gravitational wave signal before
ringdown. This enables the parameter estimation to be conducted in the
frequency domain, which is mathematically equivalent to the time domain method.
We keep the settings as similar as possible to the previous studies by
\textcite{Cotesta:2022pci} and Isi \textit{et
al.}\cite{Isi:2019aib,Isi:2022mhy} which yielded conflicting results on the
Bayes factor of the overtone. We examine the spectral contents of the
matched-filtering in the frequency domain, and propose a convergence test to
assess the validity of an overtone model. Our results find the Bayes factors
for the overtone fall within and around a range of times centered at
the best-fit merger time of GW150914, which supports the existence of an
overtone in agreement with the conclusions of Isi \textit{et
al.}\cite{Isi:2019aib,Isi:2022mhy}. Our work contributes to the understanding
of how various methods affect the statistical significance of overtones.Comment: 8 pages, 7 figures. Data release at
https://github.com/gwastro/gw150914-overtone. Comments welcome
Spectroscopy for asymmetric binary black hole mergers
We study Bayesian inference of black hole ringdown modes for simulated binary
black hole signals. We consider to what extent different fundamental ringdown
modes can be identified in the context of black hole spectroscopy. Our
simulated signals are inspired by the high mass event GW190521. We find strong
correlation between mass ratio and Bayes factors of the subdominant ringdown
modes. The Bayes factor values and time dependency, and the peak time of the
(3,3,0) mode align with those found analysing the real event GW190521,
particularly for high-mass ratio systems.Comment: 11 pages, 6 figures, 2 table
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
Spectroscopy for asymmetric binary black hole mergers
We study Bayesian inference of black hole ringdown modes for simulated binary black hole signals. We consider to what extent different fundamental ringdown modes can be identified in the context of black hole spectroscopy. Our simulated signals are inspired by the high-mass event GW190521. We find strong correlation between mass ratio and Bayes factors of the subdominant ringdown modes. The Bayes factor values and time dependency, and the peak time of the (3,3,0) mode align with those found analyzing the real event GW190521, particularly for high-mass ratio systems
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
Model systematics in time domain tests of binary black hole evolution
We perform several consistency tests between different phases of binary black
hole dynamics; the inspiral, the merger, and the ringdown on the gravitational
wave events GW150914 and GW170814. These tests are performed explicitly in the
time domain, without any spectral leakage between the different phases. We
compute posterior distributions on the mass and spin of the initial black holes
and the final black hole. We also compute the initial areas of the two
individual black holes and the final area from the parameters describing the
remnant black hole. This facilitates a test of Hawking's black hole area
theorem. We use different waveform models to quantify systematic waveform
uncertainties for the area increase law with the two events. We find that these
errors may lead to overstating the confidence with which the area theorem is
confirmed. For example, we find agreement with the area theorem for
GW150914 if a damped sinusoid consisting of a single-mode is used at merger to
estimate the final area. This is because this model overestimates the final
mass. Including an overtone of the dominant mode decreases the confidence to
; using a full merger-ringdown model further decreases the confidence
to . We find that comparing the measured change in the area to
the expected change in area yields a more robust test, as it also captures over
estimates in the change of area. We find good agreement with GR when applying
this test to GW150914 and GW170814.Comment: 11 pages, 8 figure
Black hole spectroscopy in the next decade
Gravitational wave observations of the ringdown of the remnant black hole in a binary black hole coalescence provide a unique opportunity of confronting the black hole no-hair theorem in general relativity with observational data. The most robust tests are possible if multiple ringdown modes can be observed. In this paper, using state-of-the-art Bayesian inference methods and the most up-to-date knowledge of binary black hole population parameters and ringdown mode amplitudes, we evaluate the prospects for black hole spectroscopy with current and future ground based gravitational wave detectors over the next 10 years. For different population models, we estimate the likely number of events for which the subdominant mode can be detected and distinguished from the dominant mode. We show that black hole spectroscopy could significantly test general relativity for events seen by the proposed LIGO Voyager detectors.acceptedVersio