11,943 research outputs found
Constraints on the astrophysical environment of binaries with gravitational-wave observations
No full textAims. The dynamics of coalescing compact binaries can be affected by the environment in which the systems evolve, leaving detectable signatures in the emitted gravitational signal. In this paper, we investigate the ability of gravitational-wave detectors to constrain the nature of the environment in which compact binaries merge.
Methods. We parametrized a variety of environmental effects by modifying the phase of the gravitational signal emitted by black hole and neutron star binaries. We infer the bounds on such effects by current and future generations of interferometers, studying their dependence on the binary’s parameters.
Results. We show that the strong dephasing induced by accretion and dynamical friction can constrain the density of the surrounding medium to orders of magnitude below those of accretion disks. Planned detectors, such as LISA or DECIGO, will be able to probe densities typical of those of dark matter
Radiative transfer effects on the Lya forest
No full textStrong observational evidence for a fluctuating ultraviolet background (UVB) has been accumulating through a number of studies of the HI and HeII Lyα forest as well as accurate intergalactic medium (IGM) metallicity measurements. UVB fluctuations could arise both from the inhomogeneous distribution of the ionizing sources and/or from radiative transfer (RT) through the filamentary IGM. In this study we investigate, via numerical simulations, the role of RT effects, such as shadowing, self-shielding and filtering of the ionizing radiation, in giving rise to a fluctuating UVB. We focus on possible detectable signatures of these effects on quantities derived from Lyα forest spectra, as photoionization rate fluctuations, η(≡NHeII/NHI) parameter distributions and the IGM temperature at z~ 3. We find that RT induces fluctuations up to 60 per cent in the UVB, which are tightly correlated to the density field. The UVB mean intensity is progressively suppressed toward higher densities and photon energies above 4 Ryd, due to the high HeII opacity. Shielding of overdense regions (Δ>~ 5) from cosmic HeII ionizing radiation produces a decreasing trend of η with overdensity. Furthermore, we find that the mean η value inferred from HI-HeII Lyα forest observations can be explained only by properly accounting for the actual IGM opacity. We outline and discuss several implications of our findings
Love in extrema ratio
No full textThe tidal deformability of a self-gravitating object leaves an imprint on the gravitational-wave signal of an inspiral which is paramount to measure the internal structure of the binary components. We unveil here a surprisingly unnoticed effect: in the extreme mass-ratio limit the tidal Love number of the central object (i.e. the quadrupole moment induced by the tidal field of its companion) affects the gravitational waveform at the leading order in the mass ratio. This effect acts as a magnifying glass for the tidal deformability of supermassive objects but was so far neglected, probably because the tidal Love numbers of a black hole (the most natural candidate for a compact supermassive object) are identically zero. We argue that extreme mass-ratio inspirals detectable by the future laser interferometric space antenna (LISA) mission might place constraints on the tidal Love numbers of the central object which are roughly eight orders of magnitude more stringent than current ones on neutron stars, potentially probing all models of black hole mimickers proposed so far
Low latency search for gravitational waves from black-hole-neutron-star binaries in coincidence with short gamma-ray bursts
No full textWe propose a procedure to be used in the search for gravitational waves from black-hole-neutron-star coalescing binaries, in coincidence with short gamma-ray bursts. It is based on two recently proposed semianalytic fits, one reproducing the mass of the remnant disk surrounding the black hole which forms after the merging as a function of some binary parameters, the second relating the neutron star compactness, i.e., the ratio of mass and radius, with its tidal deformability. Using a Fisher matrix analysis and the two fits, we assign a probability that the emitted gravitational signal is associated to the formation of an accreting disk massive enough to supply the energy needed to power a short gamma-ray burst. This information can be used in low-latency data analysis to restrict the parameter space searching for gravitational wave signals in coincidence with short gamma-ray bursts and to gain information on the dynamics of the coalescing system and on the internal structure of the components. In addition, when the binary parameters are measured with high accuracy, it will be possible to use this information to trigger the search for off-axis gamma-ray burst afterglows
Sensitivity of Neutron Star Observations to Three-nucleon Forces
No full textAstrophysical observations of neutron stars have been widely used to infer
the properties of the nuclear matter equation of state. Beside being a source
of information on average properties of dense matter, however, the data
provided by electromagnetic and gravitational wave (GW) facilities are reaching
the accuracy needed to constrain, for the first time, nuclear dynamics in dense
matter. In this work we assess the sensitivity of current and future neutron
star observations to directly infer the strength of repulsive three-nucleon
forces, which are key to determine the stiffness of the equation of state.
Using a Bayesian approach we focus on the constraints that can be derived on
three-body interactions from binary neutron star mergers observed by second and
third-generation of gravitational wave interferometers. We consider both single
and multiple observations. For current detectors at design sensitivity the
analysis suggests that only low mass systems, with large signal-to-noise ratios
(SNR), allow to reliably constrain the three-body forces. However, our results
show that a single observation with a third-generation interferometer, such as
the Einstein Telescope or Cosmic Explorer, will constrain the strength of the
repulsive three-body potential with exquisite accuracy, turning
third-generation GW detectors into new laboratories to study the nucleon
dynamics.Comment: Minor changes to improve the discussion of the results. Technical
details added to extend the equation of state descriptio
Interpreting the transmission windows of distant quasars
No full textWe propose the Apparent Shrinking Criterion (ASC) to interpret the spatial
extent, R_w, of transmitted flux windows in the absorption spectra of high-z
quasars. The ASC can discriminate between the two regimes in which R_w
corresponds either to the physical size, R_HII, of the quasar HII region, or to
the distance, R^max_w, at which the transmitted flux drops to =0.1 and a
Gunn-Peterson (GP) trough appears. In the first case (HR regime), one can
determine the IGM mean HI fraction, x_HI; in the second (PR regime), the value
of R_w allows to measure the local photoionization rate and the local
enhancement of the photoionization rate, Gamma_G, due to nearby/intervening
galaxies. The ASC has been tested against radiative transfer+SPH numerical
simulations, and applied to 15 high-z (z>5.8) quasars sample from Fan et al.
(2006). All sample quasars are found to be in the PR regime; hence, their
observed spectral properties (inner flux profile, extent of transmission
window) cannot reliably constrain the value of x_HI. Four sample quasars show
evidence for a local enhancement (up to 50%) in the local photoionization rate
possibly produced by a galaxy overdensity. We discuss the possible
interpretations and uncertainties of this result
DRUBER: a trustable decentralized drone-based delivery system
No full textIn the latest years, there has been a growing interest in autonomous drone delivery. This is due to the increasing demand for efficient delivery services, and to the concurrent inability of existing ground based systems to provide guaranteed availability, and delivery time. However, the cost for implementing a centralized drone-based delivery service can only be afforded by large commercial organizations.
To face this issue we propose Druber, a fully distributed service based on a fleet of coordinated drones, belonging to multiple owners. With Druber, delivery of a parcel is provided by several drones, with intermediate pit stops for battery replacement or drone-to-drone parcel handovers. The use of a federated approach eliminates the need of a single company investment and guarantees a quickly deployable, highly scalable, and inexpensive architecture. Nevertheless, it introduces a problem of trust: can users rely on private drone owners? To guarantee a trustable service Druber leverages blockchain features to develop and control the entire delivery chain. Our evaluation shows an impressive advantage of our platform with respect to existing ground based services in terms of service cost and parcel delivery time, at the expense of a negligible delay for the management of blockchain operations
Andrea Bacová
No full textAndrea Bacová focuses on research and teaching in the field of residential architecture. Her work includes systematic research on residential buildings and their urban context. She actively participates in promoting Slovak architecture and is the author of several publications and exhibitions
Solving the relativistic inverse stellar problem through gravitational waves observation of binary neutron stars
No full textThe LIGO/Virgo Collaboration has recently announced the direct detection of gravitational waves emitted in the coalescence of a neutron star binary. This discovery allows, for the first time, to set new constraints on the behavior of matter at supranuclear density, complementary with those coming from astrophysical observations in the electromagnetic band. In this paper we demonstrate the feasibility of using gravitational signals to solve the relativistic inverse stellar problem, i.e., to reconstruct the parameters of the equation of state (EoS) from measurements of the stellar mass and tidal Love number. We perform Bayesian inference of mock data, based on different models of the star internal composition, modeled through piecewise polytropes. Our analysis shows that the detection of a small number of sources by a network of advanced interferometers would allow to put accurate bounds on the EoS parameters, and to perform a model selection among the realistic equations of state proposed in the literature
Modeling frequency-dependent tidal deformability for environmental black hole mergers
No full textMotivated by events in which black holes can lose their environment due to tidal interactions in a binary system, we develop a waveform model in which the tidal deformability interpolates between a finite value (dressed black hole) at relatively low frequency and a zero value (naked black hole) at high frequency. We then apply this model to the example case of a black hole dressed with an ultralight scalar field and investigate the detectability of the tidal Love number with the Einstein Telescope. We show that the parameters of the tidal deformability model could be measured with high accuracy, providing a useful tool to understand dynamical environmental effects taking place during the inspiral of a binary system
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