0000000001210839
AUTHOR
Nicolas Sanchis-gual
showing 55 related works from this author
GW170817: Implications for the Stochastic Gravitational-Wave Background from Compact Binary Coalescences
2018
The LIGO Scientific and Virgo Collaborations have announced the first detection of gravitational waves from the coalescence of two neutron stars. The merger rate of binary neutron stars estimated from this event suggests that distant, unresolvable binary neutron stars create a significant astrophysical stochastic gravitational-wave background. The binary neutron star background will add to the background from binary black holes, increasing the amplitude of the total astrophysical background relative to previous expectations. In the Advanced LIGO-Virgo frequency band most sensitive to stochastic backgrounds (near 25 Hz), we predict a total astrophysical background with amplitude $\Omega_{\rm…
Dynamical formation of a hairy black hole in a cavity from the decay of unstable solitons
2016
Recent numerical relativity simulations within the Einstein--Maxwell--(charged-)Klein-Gordon (EMcKG) system have shown that the non-linear evolution of a superradiantly unstable Reissner-Nordstr\"om black hole (BH) enclosed in a cavity, leads to the formation of a BH with scalar hair. Perturbative evidence for the stability of such hairy BHs has been independently established, confirming they are the true endpoints of the superradiant instability. The same EMcKG system admits also charged scalar soliton-type solutions, which can be either stable or unstable. Using numerical relativity techniques, we provide evidence that the time evolution of some of these $\textit{unstable}$ solitons leads…
All-sky search in early O3 LIGO data for continuous gravitational-wave signals from unknown neutron stars in binary systems
2021
Rapidly spinning neutron stars are promising sources of continuous gravitational waves. Detecting such a signal would allow probing of the physical properties of matter under extreme conditions. A significant fraction of the known pulsar population belongs to binary systems. Searching for unknown neutron stars in binary systems requires specialized algorithms to address unknown orbital frequency modulations. We present a search for continuous gravitational waves emitted by neutron stars in binary systems in early data from the third observing run of the Advanced LIGO and Advanced Virgo detectors using the semicoherent, GPU-accelerated, binaryskyhough pipeline. The search analyzes the most s…
Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background
2018
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually-unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generic…
Search for anisotropic gravitational-wave backgrounds using data from Advanced LIGO and Advanced Virgo's first three observing runs
2021
We report results from searches for anisotropic stochastic gravitational-wave backgrounds using data from the first three observing runs of the Advanced LIGO and Advanced Virgo detectors. For the first time, we include Virgo data in our analysis and run our search with a new efficient pipeline called {\tt PyStoch} on data folded over one sidereal day. We use gravitational-wave radiometry (broadband and narrow band) to produce sky maps of stochastic gravitational-wave backgrounds and to search for gravitational waves from point sources. A spherical harmonic decomposition method is employed to look for gravitational-wave emission from spatially-extended sources. Neither technique found eviden…
All-sky search for long-duration gravitational wave transients in the first Advanced LIGO observing run
2018
Made available in DSpace on 2018-11-26T17:45:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-03-22 Australian Research Council Council of Scientific and Industrial Research of India Department of Science and Technology, India Science AMP; Engineering Research Board (SERB), India Ministry of Human Resource Development, India Spanish Agencia Estatal de Investigacion Vicepresidencia i Conselleria d'Innovacio, Recerca i Turisme Conselleria d'Educacio i Universitat del Govern de les Illes Balears Conselleria d'Educacio, Investigacio, Cultura i Esport de la Generalitat Valenciana National Science Centre of Poland Swiss National Science Foundation (SNSF) Russian Foundation for Basic Rese…
Stability and physical properties of spherical excited scalar boson stars
2023
We study the time evolution of spherical, excited -- with $n$ radial nodes -- scalar boson stars in General Relativity minimally coupled to a complex massive scalar field with quartic self-interactions. We report that these stars, with up to $n=10$, can be made dynamically stable, up to timescales of $t\sim\frac{10^{4}}{c\mu}$, where $\mu$ is the inverse Compton wavelength of the scalar particle, for sufficiently large values of the self-interactions coupling constant $\lambda$, which depend on $n$. We observe that the compactness of these solutions is rather insensitive to $n$, for large $\lambda$ and fixed frequency. Generically, along the branches where stability was studied, these excit…
GW190521 as a Merger of Proca Stars: A Potential New Vector Boson of 8.7×10−13 eV
2021
Advanced LIGO-Virgo have reported a short gravitational-wave signal (GW190521) interpreted as a quasicircular merger of black holes, one at least populating the pair-instability supernova gap, that formed a remnant black hole of ${M}_{f}\ensuremath{\sim}142\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ at a luminosity distance of ${d}_{L}\ensuremath{\sim}5.3\text{ }\text{ }\mathrm{Gpc}$. With barely visible pre-merger emission, however, GW190521 merits further investigation of the pre-merger dynamics and even of the very nature of the colliding objects. We show that GW190521 is consistent with numerically simulated signals from head-on collisions of two (equal mass and spin) horizonless vecto…
Quasistationary solutions of self-gravitating scalar fields around black holes
2015
Recent perturbative studies have shown the existence of long-lived, quasistationary configurations of scalar fields around black holes. In particular, such configurations have been found to survive for cosmological time scales, which is a requirement for viable dark matter halo models in galaxies based on such types of structures. In this paper we perform a series of numerical relativity simulations of dynamical nonrotating black holes surrounded by self-gravitating scalar fields. We solve numerically the coupled system of equations formed by the Einstein and the Klein-Gordon equations under the assumption of spherical symmetry using spherical coordinates. Our results confirm the existence …
Gravitational waves from binary black hole mergers surrounded by scalar field clouds: Numerical simulations and observational implications
2020
We show how gravitational-wave observations of binary black hole (BBH) mergers can constrain the physical characteristics of a scalar field cloud parameterized by mass $\tilde{\mu}$ and strength $\phi_0$ that may surround them. We numerically study the inspiraling equal-mass, non-spinning BBH systems dressed in such clouds, focusing especially on the gravitational-wave signals emitted by their merger-ringdown phase. These waveforms clearly reveal that larger values of $\tilde{\mu}$ or $\phi_0$ cause bigger changes in the amplitude and frequency of the scalar-field-BBH ringdown signals. We show that the numerical waveforms of scalar-field-BBHs can be modelled as chirping sine-Gaussians, with…
Tests of General Relativity with GW170817
2019
The recent discovery by Advanced LIGO and Advanced Virgo of a gravitational wave signal from a binary neutron star inspiral has enabled tests of general relativity (GR) with this new type of source. This source, for the first time, permits tests of strong-field dynamics of compact binaries in presence of matter. In this paper, we place constraints on the dipole radiation and possible deviations from GR in the post-Newtonian coefficients that govern the inspiral regime. Bounds on modified dispersion of gravitational waves are obtained; in combination with information from the observed electromagnetic counterpart we can also constrain effects due to large extra dimensions. Finally, the polari…
Erratum: “Searches for Gravitational Waves from Known Pulsars at Two Harmonics in 2015–2017 LIGO Data” (2019, ApJ, 879, 10)
2019
Two analysis errors have been identified that affect the results for a handful of the high-value pulsars given in Table 1 of Abbott et al. (2019). One affects the Bayesian analysis for the five pulsars that glitched during the analysis period, and the other affects the 5n-vector analysis for J0711-6830. Updated results after correcting the errors are shown in Table 1, which now supersedes the results given for those pulsars in Table 1 of Abbott et al. (2019). Updated versions of figures can be seen in Figures 1-4. Bayesian analysis.-For the glitching pulsars, the signal phase evolution caused by the glitch was wrongly applied twice and was therefore not consistent with our expected model of…
Status of Advanced Virgo
2017
The LIGO and the Virgo collaborations have recently announced the first detections of Gravitational Waves. Due to their weak amplitude, Gravitational Waves are expected to produce a very small effect on free-falling masses, which undergo a displacement of the order of 10-18 m for a Km-scale mutual distance. This discovery showed that interferometric detectors are suitable to reveal such a feeble effect, and therefore represent a new tool for astronomy, astrophysics and cosmology in the understanding of the Universe. To better reconstruct the position of the Gravitational Wave source and increase the signal-to-noise ratio of the events by means of multiple coincidence, a network of detectors…
Dynamical formation of a Reissner-Nordström black hole with scalar hair in a cavity
2016
In a recent Letter [Sanchis-Gual et al., Phys. Rev. Lett. 116, 141101 (2016)], we presented numerical relativity simulations, solving the full Einstein--Maxwell--Klein-Gordon equations, of superradiantly unstable Reissner-Nordstr\"om black holes (BHs), enclosed in a cavity. Low frequency, spherical perturbations of a charged scalar field trigger this instability. The system's evolution was followed into the nonlinear regime, until it relaxed into an equilibrium configuration, found to be a hairy BH: a charged horizon in equilibrium with a scalar field condensate, whose phase is oscillating at the (final) critical frequency. Here, we investigate the impact of adding self-interactions to the …
Synchronised gravitational atoms from mergers of bosonic stars
2020
If ultralight bosonic fields exist in Nature as dark matter, superradiance spins down rotating black holes (BHs), dynamically endowing them with equilibrium bosonic clouds, here dubbed synchronised gravitational atoms (SGAs). The self-gravity of these same fields, on the other hand, can lump them into (scalar or vector) horizonless solitons known as bosonic stars (BSs). We show that the dynamics of BSs yields a new channel forming SGAs. We study BS binaries that merge to form spinning BHs. After horizon formation, the BH spins up by accreting the bosonic field, but a remnant lingers around the horizon. If just enough angular momentum is present, the BH spin up stalls precisely as the remnan…
Confusing Head-On Collisions with Precessing Intermediate-Mass Binary Black Hole Mergers
2021
We report a degeneracy between the gravitational-wave signals from quasi-circular precessing black-hole mergers and those from extremely eccentric mergers, namely head-on collisions. Performing model selection on numerically simulated signals of head-on collisions using models for quasi-circular binaries we find that, for signal-to-noise ratios of 15 and 25, typical of Advanced LIGO observations, head-on mergers with respective total masses of $M\in (125,300)M_\odot$ and $M\in (200,440)M_\odot$ would be identified as precessing quasi-circular intermediate-mass black hole binaries, located at a much larger distance. Ruling out the head-on scenario would require to perform model selection usi…
Quasistationary solutions of scalar fields around collapsing self-interacting boson stars
2017
There is increasing numerical evidence that scalar fields can form long-lived quasibound states around black holes. Recent perturbative and numerical relativity calculations have provided further confirmation in a variety of physical systems, including both static and accreting black holes, and collapsing fermionic stars. In this work, we investigate this issue yet again in the context of gravitationally unstable boson stars leading to black-hole formation. We build a large sample of spherically symmetric initial models, both stable and unstable, incorporating a self-interaction potential with a quartic term. The three different outcomes of unstable models, namely, migration to the stable b…
Multi-field, multi-frequency bosonic stars and a stabilization mechanism
2021
Scalar bosonic stars (BSs) stand out as a multi-purpose model of exotic compact objects. We enlarge the landscape of such (asymptotically flat, stationary, everywhere regular) objects by considering multiple fields (possibly) with different frequencies. This allows for new morphologies ${\it and}$ a stabilization mechanism for different sorts of unstable BSs. First, any odd number of complex fields, yields a continuous family of BSs departing from the spherical, equal frequency, $\ell-$BSs. As the simplest illustration, we construct the $\ell$ = ${\it 1}$ ${\it BSs}$ ${\it family}$, that includes several single frequency solutions, including even parity (such as spinning BSs and a toroidal,…
GW190521: A Binary Black Hole Merger with a Total Mass of 150 M⊙
2020
LIGO Scientific Collaboration and Virgo Collaboration: et al.
Advanced Virgo Status
2015
Abstract The detection of a gravitational wave signal in September 2015 by LIGO interferometers, announced jointly by LIGO collaboration and Virgo collaboration in February 2016, opened a new era in Astrophysics and brought to the whole community a new way to look at - or “listen” to - the Universe. In this regard, the next big step was the joint observation with at least three detectors at the same time. This configuration provides a twofold benefit: it increases the signal-to-noise ratio of the events by means of triple coincidence and allows a narrower pinpointing of GW sources, and, in turn, the search for Electromagnetic counterparts to GW signals. Advanced Virgo (AdV) is the second ge…
Spontaneous creation of circularly polarized photons in chiral astrophysical systems
2020
This work establishes a relation between chiral anomalies in curved spacetimes and the radiative content of the gravitational field. In particular, we show that a flux of circularly polarized gravitational waves triggers the spontaneous creation of photons with net circular polarization from the quantum vacuum. Using waveform catalogues we identify precessing binary black holes as astrophysical configurations that emit such gravitational radiation, and then solve the fully non-linear Einstein's equations with numerical relativity to evaluate the net effect. The quantum amplitude for a merger is comparable to the Hawking emission rate of the final black hole, and small to be directly observe…
Can fermion-boson stars reconcile multi-messenger observations of compact stars?
2021
Mixed fermion-boson stars are stable, horizonless, everywhere regular solutions of the coupled Einstein-(complex, massive) Klein-Gordon-Euler system. While isolated neutron stars and boson stars are uniquely determined by their central energy density, mixed configurations conform an extended parameter space that depends on the combination of the number of fermions and (ultra-light) bosons. The wider possibilities offered by fermion-boson stars could help explain the tension in the measurements of neutron star masses and radii reported in recent multi-messenger observations and nuclear-physics experiments. In this work we construct equilibrium configurations of mixed fermion-boson stars with…
Neutron star collapse and gravitational waves with a non-convex equation of state
2018
The thermodynamical properties of the equation of state (EoS) of high-density matter (above nuclear saturation density) and the possible existence of exotic states such as phase transitions from nuclear/hadronic matter into quark-gluon plasma, or the appearance of hyperons, may critically influence the stability and dynamics of compact relativistic stars. From a theoretical point of view, establishing the existence of those states requires the analysis of the `convexity' of the EoS. We show indications of the existence of regions in the dense-matter EoS where the thermodynamics may be non-convex as a result of a non-monotonic dependence of the sound speed with the rest-mass density. When th…
Nonlinear dynamics of spinning bosonic stars: formation and stability
2019
We perform numerical evolutions of the fully non-linear Einstein-(complex, massive)Klein-Gordon and Einstein-(complex)Proca systems, to assess the formation and stability of spinning bosonic stars. In the scalar/vector case these are known as boson/Proca stars. Firstly, we consider the formation scenario. Starting with constraint-obeying initial data, describing a dilute, axisymmetric cloud of spinning scalar/Proca field, gravitational collapse towards a spinning star occurs, via gravitational cooling. In the scalar case the formation is transient, even for a non-perturbed initial cloud; a non-axisymmetric instability always develops ejecting all the angular momentum from the scalar star. I…
Completion of the universal I-Love-Q relations in compact stars including the mass
2017
In a recent paper we applied a rigorous perturbed matching framework to show the amendment of the mass of rotating stars in Hartle's model. Here, we apply this framework to the tidal problem in binary systems. Our approach fully accounts for the correction to the Love numbers needed to obtain the universal $I$-Love-$Q$ relations. We compute the corrected mass vs radius configurations of rotating quark stars, revisiting a classical paper on the subject. These corrections allow us to find a universal relation involving the second-order contribution to the mass $\delta M$. We thus complete the set of universal relations for the tidal problem in binary systems, involving four perturbation param…
GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence
2017
On August 14, 2017 at 10 30:43 UTC, the Advanced Virgo detector and the two Advanced LIGO detectors coherently observed a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes, with a false-alarm rate of 1 in 27 000 years. The signal was observed with a three-detector network matched-filter signal-to-noise ratio of 18. The inferred masses of the initial black holes are 30.5-3.0+5.7M and 25.3-4.2+2.8M (at the 90% credible level). The luminosity distance of the source is 540-210+130 Mpc, corresponding to a redshift of z=0.11-0.04+0.03. A network of three detectors improves the sky localization of the source, reducing the area of the 90% credible regio…
Constraining the p -Mode– g -Mode Tidal Instability with GW170817
2019
We analyze the impact of a proposed tidal instability coupling p modes and g modes within neutron stars on GW170817. This nonresonant instability transfers energy from the orbit of the binary to internal modes of the stars, accelerating the gravitational-wave driven inspiral. We model the impact of this instability on the phasing of the gravitational wave signal using three parameters per star: An overall amplitude, a saturation frequency, and a spectral index. Incorporating these additional parameters, we compute the Bayes factor (lnB!pgpg) comparing our p-g model to a standard one. We find that the observed signal is consistent with waveform models that neglect p-g effects, with lnB!pgpg=…
The advanced Virgo longitudinal control system for the O2 observing run
2020
Following a successful period of data-taking between 2006 and 2011, the Virgo gravitational-wave detector was taken offline for a major upgrade. The changes made to the instrument significantly increased the complexity of the control systems and meant that an extended period of commissioning was required to reach a sensitivity appropriate for science data-taking. This commissioning period was completed in July of 2017 and the second-generation Advanced Virgo detector went on to join the Advanced LIGO detectors in the O2 science run in August of the same year. The upgraded detector was approximately twice as sensitive to binary neutron star mergers as the first-generation instrument. During …
Quasistationary solutions of scalar fields around accreting black holes
2016
Massive scalar fields can form long-lived configurations around black holes. These configurations, dubbed quasi-bound states, have been studied both in the linear and nonlinear regimes. In this paper we show that quasi-bound states can form in a dynamical scenario in which the mass of the black hole grows significantly due to the capture of infalling matter. We solve the Klein-Gordon equation numerically in spherical symmetry, mimicking the evolution of the spacetime through a sequence of analytic Schwarzschild black hole solutions of increasing mass. It is found that the frequency of oscillation of the quasi-bound states decreases as the mass of the black hole increases. In addition, accre…
Head-on collisions and orbital mergers of Proca stars
2019
Proca stars are self-gravitating Bose-Einstein condensates obtained as numerical stationary solutions of the Einstein-(complex)-Proca system. These solitonic can be both stable and form dynamically from generic initial data by the mechanism of gravitational cooling. In this paper we further explore the dynamical properties of these solitonic objects by performing both head-on collisions and orbital mergers of equal mass Proca stars, using fully non-linear numerical evolutions. For the head-on collisions, we show that the end point and the gravitational waveform from these collisions depends on the compactness of the Proca star. Proca stars with sufficiently small compactness collide leaving…
All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO O2 data
2019
We present results of an all-sky search for continuous gravitational waves (CWs), which can be produced by fast-spinning neutron stars with an asymmetry around their rotation axis, using data from the second observing run of the Advanced LIGO detectors. We employ three different semi-coherent methods ($\textit{FrequencyHough}$, $\textit{SkyHough}$, and $\textit{Time-Domain $\mathcal{F}$-statistic}$) to search in a gravitational-wave frequency band from 20 to 1922 Hz and a first frequency derivative from $-1\times10^{-8}$ to $2\times10^{-9}$ Hz/s. None of these searches has found clear evidence for a CW signal, so we present upper limits on the gravitational-wave strain amplitude $h_0$ (the …
GW190412: Observation of a binary-black-hole coalescence with asymmetric masses
2020
LIGO Scientific Collaboration and Virgo Collaboration: et al.
Comparison between the fCCZ4 and BSSN formulations of Einstein equations in spherical polar coordinates
2015
Recently, we generalized a covariant and conformal version of the Z4 system of the Einstein equations using a reference metric approach, that we denote as fCCZ4. We successfully implemented and tested this approach in a 1D code that uses spherical coordinates and assumes spherical symmetry, obtaining from one to three orders of magnitude reduction of the Hamiltonian constraint violations with respect to the BSSN formulation in tests involving neutron star spacetimes. In this work, we show preliminary results obtained with the 3D implementation of the fCCZ4 formulation in a fully 3D code using spherical polar coordinates.
Explosion and Final State of an Unstable Reissner-Nordström Black Hole
2016
A Reissner-Nordstr\"om black hole (BH) is superradiantly unstable against spherical perturbations of a charged scalar field, enclosed in a cavity, with frequency lower than a critical value. We use numerical relativity techniques to follow the development of this unstable system -- dubbed a charged BH bomb -- into the non-linear regime, solving the full Einstein--Maxwell--Klein-Gordon equations, in spherical symmetry. We show that: $i)$ the process stops before all the charge is extracted from the BH; $ii)$ the system settles down into a hairy BH: a charged horizon in equilibrium with a scalar field condensate, whose phase is oscillating at the (final) critical frequency. For low scalar fie…
Gravitational-wave Constraints on the Equatorial Ellipticity of Millisecond Pulsars
2020
We present a search for continuous gravitational waves from five radio pulsars, comprising three recycled pulsars (PSR J0437-4715, PSR J0711-6830, and PSR J0737-3039A) and two young pulsars: the Crab pulsar (J0534+2200) and the Vela pulsar (J0835-4510). We use data from the third observing run of Advanced LIGO and Virgo combined with data from their first and second observing runs. For the first time, we are able to match (for PSR J0437-4715) or surpass (for PSR J0711-6830) the indirect limits on gravitational-wave emission from recycled pulsars inferred from their observed spin-downs, and constrain their equatorial ellipticities to be less than 10-8. For each of the five pulsars, we perfor…
GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
2017
On August 17, 2017 at 12-41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their first observation of a binary neutron star inspiral. The signal, GW170817, was detected with a combined signal-to-noise ratio of 32.4 and a false-alarm-rate estimate of less than one per 8.0×104 years. We infer the component masses of the binary to be between 0.86 and 2.26 M, in agreement with masses of known neutron stars. Restricting the component spins to the range inferred in binary neutron stars, we find the component masses to be in the range 1.17-1.60 M, with the total mass of the system 2.74-0.01+0.04M. The source was localized within a sky region of 28 deg2 (90% probabili…
A Gravitational-wave Measurement of the Hubble Constant Following the Second Observing Run of Advanced LIGO and Virgo
2021
This paper presents the gravitational-wave measurement of the Hubble constant (H 0) using the detections from the first and second observing runs of the Advanced LIGO and Virgo detector network. The presence of the transient electromagnetic counterpart of the binary neutron star GW170817 led to the first standard-siren measurement of H 0. Here we additionally use binary black hole detections in conjunction with galaxy catalogs and report a joint measurement. Our updated measurement is H 0 = km s-1 Mpc-1 (68.3% of the highest density posterior interval with a flat-in-log prior) which is an improvement by a factor of 1.04 (about 4%) over the GW170817-only value of km s-1 Mpc-1. A significant …
Fully Covariant and Conformal Formulation of the Z4 System Compared to the BSSN Formulation in Spherical Symmetry
2014
We have generalized a covariant and conformal version of the Z4 system of the Einstein equations by adopting a reference metric approach, that we denote as fCCZ4, well suited for curvilinear as well as Cartesian coordinates. We implement this formalism in spherical polar coordinates under the assumption of spherical symmetry using a partially-implicit Runge-Kutta (PIRK) method, without using any regularization scheme, and show that our code can evolve both vacuum and non-vacuum spacetimes without encountering instabilities. We have performed several tests and compared the Hamiltonian constraint violations of the fCCZ4 system, for different choices of certain free parameters, with these of B…
Quasistationary solutions of self-gravitating scalar fields around collapsing stars
2015
Recent work has shown that scalar fields around black holes can form long-lived, quasistationary configurations surviving for cosmological time scales. Scalar fields thus cannot be discarded as viable candidates for dark matter halo models in galaxies around central supermassive black holes (SMBHs). One hypothesized formation scenario of most SMBHs at high redshift is the gravitational collapse of supermassive stars (SMSs) with masses of $\ensuremath{\sim}{10}^{5}\text{ }\text{ }{\mathrm{M}}_{\ensuremath{\bigodot}}$. Any such scalar field configurations must survive the gravitational collapse of a SMS in order to be a viable model of physical reality. To check for the postcollapse survival …
Dynamical bar-mode instability in spinning bosonic stars
2020
Spinning bosonic stars (SBSs) can form from the gravitational collapse of a dilute cloud of scalar/Proca particles with nonzero angular momentum, via gravitational cooling. The scalar stars are, however, transient due to a nonaxisymmetric instability which triggers the loss of angular momentum. By contrast, no such instability was observed for the fundamental ( m = 1 ) Proca stars. In [N. Sanchis-Gual et al., Phys. Rev. Lett. 123, 221101 (2019)] we tentatively related the different stability properties to the different toroidal/spheroidal morphology of the scalar/Proca models. Here, we continue this investigation, using three-dimensional numerical-relativity simulations of the Einstein-(mas…
All-sky search for short gravitational-wave bursts in the second Advanced LIGO and Advanced Virgo run
2019
We present the results of a search for short-duration gravitational-wave transients in the data from the second observing run of Advanced LIGO and Advanced Virgo. We search for gravitational-wave transients with a duration of milliseconds to approximately one second in the 32-4096 Hz frequency band with minimal assumptions about the signal properties, thus targeting a wide variety of sources. We also perform a matched-filter search for gravitational-wave transients from cosmic string cusps for which the waveform is well-modeled. The unmodeled search detected gravitational waves from several binary black hole mergers which have been identified by previous analyses. No other significant event…
Cosmological analogies in the search for new physics in high-energy collisions
2020
In this paper, analogies between multiparticle production in high-energy collisions and the time evolution of the early universe are discussed. A common explanation is put forward under the assumption of an unconventional early state: a rapidly expanding universe before recombination (last scattering surface), followed by the CMB, later evolving up to present days, versus the formation of hidden/dark states in hadronic collisions followed by a conventional QCD parton shower yielding final-state particles. In particular, long-range angular correlations are considered pointing out deep connections between the two physical cases potentially useful for the discovery of new physics.
Search for Subsolar-Mass Ultracompact Binaries in Advanced LIGO's First Observing Run
2018
We present the first Advanced LIGO and Advanced Virgo search for ultracompact binary systems with component masses between 0.2 $M_\odot$ - 1.0 $M_\odot$ using data taken between September 12, 2015 and January 19, 2016. We find no viable gravitational wave candidates. Our null result constrains the coalescence rate of monochromatic (delta function) distributions of non-spinning (0.2 $M_\odot$, 0.2 $M_\odot$) ultracompact binaries to be less than $1.0 \times 10^6 \text{Gpc}^{-3} \text{yr}^{-1}$ and the coalescence rate of a similar distribution of (1.0 $M_\odot$, 1.0 $M_\odot$) ultracompact binaries to be less than $1.9 \times 10^4 \text{Gpc}^{-3} \text{yr}^{-1}$ (at 90 percent confidence). N…
Spontaneous Scalarization of Charged Black Holes
2018
Extended scalar-tensor-Gauss-Bonnet (eSTGB) gravity has been recently argued to exhibit spontaneous scalarisation of vacuum black holes (BHs). A similar phenomenon can be expected in a larger class of models, which includes e.g. Einstein-Maxwell-scalar (EMS) models, where spontaneous scalarisation of electrovacuum BHs should occur. EMS models have no higher curvature corrections, a technical simplification over eSTGB models that allows us to investigate, fully non-linearly, BH scalarisation in two novel directions. Firstly, numerical simulations in spherical symmetry show, dynamically, that Reissner-Nordstr\"om (RN) BHs evolve into a perturbatively stable scalarised BH. Secondly, we compute…
Dynamical formation and stability of fermion-boson stars
2020
Gravitationally bound structures composed by fermions and scalar particles known as fermion-boson stars are regular and static configurations obtained by solving the coupled Einstein-Klein-Gordon-Euler (EKGE) system. In this work, we discuss one possible scenario through which these fermion-boson stars may form by solving numerically the EKGE system under the simplifying assumption of spherical symmetry. Our initial configurations assume an already existing neutron star surrounded by an accreting cloud of a massive and complex scalar field. The results of our simulations show that once part of the initial scalar field is expelled via gravitational cooling the system gradually oscillates aro…
Dynamical formation of Proca stars and quasistationary solitonic objects
2018
We perform fully non-linear numerical simulations within the spherically symmetric Einstein-(complex)Proca system. Starting with Proca field distributions that obey the Hamiltonian, momentum and Gaussian constraints, we show that the self-gravity of the system induces the formation of compact objects, which, for appropriate initial conditions, asymptotically approach stationary soliton-like solutions known as Proca stars. The excess energy of the system is dissipated by the mechanism of \textit{gravitational cooling} in analogy to what occurs in the dynamical formation of scalar boson stars. We investigate the dependence of this process on the phase difference between the real and imaginary…
Numerical evolutions of spherical Proca stars
2017
Vector boson stars, or $\textit{Proca stars}$, have been recently obtained as fully non-linear numerical solutions of the Einstein-(complex)-Proca system. These are self-gravitating, everywhere non-singular, horizonless Bose-Einstein condensates of a massive vector field, which resemble in many ways, but not all, their scalar cousins, the well-known (scalar) $\textit{boson stars}$. In this paper we report fully-non linear numerical evolutions of Proca stars, focusing on the spherically symmetric case, with the goal of assessing their stability and the end-point of the evolution of the unstable stars. Previous results from linear perturbation theory indicate the separation between stable and…
Lensing and dynamics of ultracompact bosonic stars
2017
Spherically symmetric bosonic stars are one of the few examples of gravitating solitons that are known to form dynamically, via a classical process of (incomplete) gravitational collapse. As stationary solutions of the Einstein--Klein-Gordon or the Einstein--Proca theory, bosonic stars may also become sufficiently compact to develop light rings and hence mimic, in principle, gravitational-wave observational signatures of black holes (BHs). In this paper, we discuss how these horizonless ultra-compact objects (UCOs) are actually distinct from BHs, both phenomenologically and dynamically. In the electromagnetic channel, the light ring associated phenomenology reveals remarkable lensing patter…
Fully covariant and conformal formulation of the Z4 system in a reference-metric approach: Comparison with the BSSN formulation in spherical symmetry
2014
We adopt a reference-metric approach to generalize a covariant and conformal version of the Z4 system of the Einstein equations. We refer to the resulting system as ``fully covariant and conformal", or fCCZ4 for short, since it is well suited for curvilinear as well as Cartesian coordinates. We implement this fCCZ4 formalism in spherical polar coordinates under the assumption of spherical symmetry using a partially-implicit Runge-Kutta (PIRK) method and show that our code can evolve both vacuum and non-vacuum spacetimes without encountering instabilities. Our method does not require regularization of the equations to handle coordinate singularities, nor does it depend on constraint-preservi…
GW170817: Measurements of Neutron Star Radii and Equation of State
2018
On 17 August 2017, the LIGO and Virgo observatories made the first direct detection of gravitational waves from the coalescence of a neutron star binary system. The detection of this gravitational-wave signal, GW170817, offers a novel opportunity to directly probe the properties of matter at the extreme conditions found in the interior of these stars. The initial, minimal-assumption analysis of the LIGO and Virgo data placed constraints on the tidal effects of the coalescing bodies, which were then translated to constraints on neutron star radii. Here, we expand upon previous analyses by working under the hypothesis that both bodies were neutron stars that are described by the same equation…
Quasi-stationary solutions of self-gravitating scalar fields around black holes
2014
Recent perturbative studies have shown the existence of long-lived, quasi-stationary configurations of scalar fields around black holes. In particular, such configurations have been found to survive for cosmological timescales, which is a requirement for viable dark matter halo models in galaxies based on such type of structures. In this paper we perform a series of numerical relativity simulations of dynamical non-rotating black holes surrounded by self-gravitating scalar fields. We solve numerically the coupled system of equations formed by the Einstein and the Klein-Gordon equations under the assumption of spherical symmetry using spherical coordinates. Our results confirm the existence …
Boson stars in Palatini $f(\mathcal{R})$ gravity
2021
We explore equilibrium solutions of spherically symmetric boson stars in the Palatini formulation of $f(\mathcal{R})$ gravity. We account for the modifications introduced in the gravitational sector by using a recently established correspondence between modified gravity with scalar matter and general relativity with modified scalar matter. We focus on the quadratic theory $f(\mathcal{R})=R+\xi R^2$ and compare its solutions with those found in general relativity, exploring both positive and negative values of the coupling parameter $\xi$. As matter source, a complex, massive scalar field with and without self-interaction terms is considered. Our results show that the existence curves of bos…
GW190521 as a merger of Proca stars: a potential new vector boson of $8.7 \times 10^{-13}$ eV
2020
Advanced LIGO-Virgo reported a short gravitational-wave signal (GW190521) interpreted as a quasi-circular merger of black holes, one populating the pair-instability supernova gap, forming a remnant black hole of $M_f\sim 142 M_\odot$ at a luminosity distance of $d_L \sim 5.3$ Gpc. With barely visible pre-merger emission, however, GW190521 merits further investigation of the pre-merger dynamics and even of the very nature of the colliding objects. We show that GW190521 is consistent with numerically simulated signals from head-on collisions of two (equal mass and spin) horizonless vector boson stars (aka Proca stars), forming a final black hole with $M_f = 231^{+13}_{-17}\,M_\odot$, located …
Precessing binary black holes as engines of electromagnetic helicity
2023
We show that binary black hole mergers with precessing evolution can potentially excite photons from the quantum vacuum in such a way that total helicity is not preserved in the process. Helicity violation is allowed by quantum fluctuations that spoil the electric-magnetic duality symmetry of the classical Maxwell theory without charges. We show here that precessing binary black hole systems in astrophysics generate a flux of circularly polarized gravitational waves which, in turn, provides the required helical background that triggers this quantum effect. Solving the fully non-linear Einstein's equations with numerical relativity we explore the parameter space of binary systems and extract…
On the dynamical bar-mode instability in spinning bosonic stars
2020
Spinning bosonic stars (SBSs) can form from the gravitational collapse of a dilute cloud of scalar/Proca particles with non-zero angular momentum. In a recent work we found that the scalar stars are transient due to a non-axisymmetric instability which triggers the loss of angular momentum. We further study the dynamical formation of SBSs using 3-dimensional numerical-relativity simulations of the Einstein-(massive, complex)Klein-Gordon system and of the Einstein-(complex)Proca system. We incorporate a quartic self-interaction potential in the scalar case to gauge its effect on the instability; we investigate (m=2) Proca stars to assess their stability; we attempt to relate the instability …