arXiv subjects
Publications and source records attributed to Osvaldo M. Moreschi.
This work introduces a geometrical method for analyzing transient gravitational waves recorded at interferometric observatories. This approach is intended to aid in assessing the performance and sensitivity of next-generation detector configurations, such as Cosmic Explorer, Einstein Telescope, and the South American Gravitational-wave Observatory.
The images of Sagittarius A${}^*$ published by the Event Horizon Telescope (ETH) Collaboration in 2022 present features that were associated with an emission ring consistent with what is expected from an accretion disc surrounding the supermassive black hole at the center of our Galaxy. Here, we generate images of Sgr~A${}^*$ across different configurations of a simple accretion disc model that became successful, in our previous work, in reproducing the main features observed in M87*. Their best image, here reproduced in Fig. 1, suggests a geometric configuration of an inclined disk with three bright regions; which we have considered as our first configuration. Since we were not convinced with the results of this first configuration, we also explore in detail the case of nearly edge-on orientations which are a priori the expected geometry for a relaxed disc, as seen from the plane of the galaxy. We have produced simulated images using an efficient ray tracing and geodesic deviation methodology that allows to account for deformation, relativistic and magnification effects. We compare our synthetic images with the EHT images reconstructed with data from April 6 and 7 of 2017. We found that, although the EHT Collaboration seems to discard the image from April 6, our best suggested image resembles the output from the {\sc Themis} pipeline for April 6; which for us gives support for the edge-on configuration.
The detections\citep{KAGRA:2023pio,LIGOScientific:2019lzm} and analysis of gravitational waves(GWs) have introduced us in a new era of our understanding of the cosmos, providing new insights into astrophysical systems involving massive objects as black holes and neutron stars. Normally the precise sky localization of a GW source needs data from three or more observatories\citep{LIGOScientific:2016lio,Abbott:2017oio}. However, the results presented in this article demonstrate that it is in fact possible to obtain the position of a GW source in a small region of the celestial sphere using data from just two GW observatories, in this case LIGO Hanford and LIGO Livingston. Furthermore, we are also able to reconstruct the gravitational-wave polarization\citep{Poisson2014} modes(PMs) for the GW170104\citep{Abbott:2017vtc} and GW150914\citep{TheLIGOScientific:2016qqj} events, with data from only these two detectors. The procedure only uses the spin 2 properties of the GW, so that it does not rely on specific assumptions on the nature of the source. Our findings are possible through careful data filtering methods\citep{Moreschi:2019vxw}, the use of refined signal processing algorithms\citep{Moreschi:2024njx}, and the application of dedicated denoising\citep{Mallat2009} techniques. This progress in the GW studies represents the first instance of a direct measurement of PMs using such a limited observational data. We provide detailed validation through the reconstruction of PMs for different polarization angles, and calculations of residuals for the GW170104 event. We also test the procedure with synthetic data with ten different source locations and polarization angles.
We report on the new developments of the procedure L2D+PMR for sky localization\citep{KAGRA:2013rdx} using data from two gravitational-wave detectors and the reconstruction of gravitational-wave polarization modes\citep{Poisson2014}, which we have previously presented\citep{Moreschi25a}. In this case we apply our methods to the GW190521\citep{Abbott:2020tfl} event, which was recorded by three gravitational-wave observatories. We find the localization of the source close to one of the crossings of two delay rings, as expected. Thus, our results corroborate the consistency of the procedure. We compare our findings with those obtained by the LIGO/Virgo Collaborations, providing an independent assessment of gravitational-wave localization. We present the second direct measurement of spin-2 gravitational-wave polarization modes.
{Using two different approaches, we study imaging in the strong lens regime taking into account the effects of plasmatic environments on light propagation. First, we extend the use of a perturbative approach that allows us to quickly and analytically calculate the position and shape of the images of a circular source lensed by a galaxy. Such approach will be compared with that obtained from the numerical solution of the lens equations. Secondly, we introduce a 3-dimensional spheroidal model to describe the spacetime associated with the dark matter halo around the lens galaxy and an associated optical metric to incorporate the presence of the plasma medium. The (chromatic) deformation on caustic and critical curves and associated multiplicity of images is also analyzed for particular configurations.
We study simulated images generated from an accretion disk surrounding the supermassive black hole hosted in the nearby galaxy M87. We approach the problem employing very simple accreting models inspired from magnetohydrodynamical simulations and introducing a new recipe for dealing with the combined integration of the geodesic and geodesic deviation equations in Kerr spacetime, which allows for a convenient and efficient way to manage the system of equations. The geometry of the basic emission model is given by a two temperature thin disk in the equatorial plane of the black hole supplemented by an asymmetric bar structure. We show that this configuration permits to generate the most salient features appearing in the EHT Collaboration images of M87 with impressive fidelity.
The definition of well-behaved coordinate charts for black hole spacetimes can be tricky, as they can lead for example to either unphysical coordinate singularities in the metric (e.g. $r=2M$ in the Schwarzschild black hole) or to an implicit dependence of the chosen coordinate to physical relevant coordinates (e.g. the dependence of the null coordinates in the Kruskal metric). Here we discuss two approaches for coordinate choices in spherical symmetry allowing us to discuss explicitly "solitary" and spherically symmetric black holes from a regular horizon to null infinity. The first approach relies on a construction of a regular null coordinate (where regular is meant as being defined from the horizon to null infinity) given an explicit solution of the Einstein-matter equations. The second approach is based on an affine-null formulation of the Einstein equations and the respective characteristic initial value problem. In particular, we present a derivation of the Reissner-Nordström black holes expressed in terms of these regular coordinates.
We present a new measure for the comparison of unknown gravitational wave signals in two detectors, without recurring to an {\it a priori} template. We apply this measure to the LIGO data of the GW150914 event and discover that Hanford and Livingston observatories have recorded two different components of the gravitational wave polarization signal.
We provide new very simple and compact expressions for the efficient calculation of gravitational lens optical scalars for Kerr spacetime which are exact along any null geodesic. These new results are obtained recurring to well known results on geodesic motion that exploit obvious and hidden symmetries of Kerr spacetime and contrast with the rather long and cumbersome expressions previously reported in the literature, providing a helpful improvement for the sake of an efficient integration of the geodesic deviation equation on Kerr geometry. We also introduce a prescription for the observer frame which captures a new notion of \emph{center of the black hole} which can be used for any position of the observer, including those near the black hole. We compare the efficient calculation of weak lens optical scalars with the exact equations; finding an excellent agreement.
We present a new strategy for the pre-processing filtering techniques of the LIGO strain of the GW150914\cite{Abbott:2016blz,TheLIGOScientific:2016wfe} event that intends to extract as much physical information as possible, minimizing the use of prior assumptions, and avoiding transformations of the astrophysical signal. The new techniques allow us to reveal more low frequency signal at earlier times, that it has been overlooked.
We present a general approach for the formulation of equations of motion for compact objects in general relativistic theories. The particle is assumed to be moving in a geometric background which in turn is asymptotically flat. Our approach defines a model for particle like objects which emphasizes different aspects of a set of gravitating objects; by concentrating in the main contributions coming from back reaction effects due to gravitational radiation.
Based in the framework of article (arXiv:1609.02110), where we have presented the general problems one encounters in the construction of balanced equations of motions for particles in relativistic theories of gravity, we present in this work the explicit balanced equations of motion for a compact object in general relativity in the harmonic gauge.
We present a convenient null gauge for the construction of the balanced equations of motion. This null gauge has the property that the asymptotic structure is intimately related to the interior one; in particular there is a strong connexion between the field equation and the balanced equations of motion. We present the balanced equations of motion in second order of the acceleration. We solve the required components of the field equation at their respective required orders, $G^2$ and $G^3$. We indicate how this approach can be extended to higher orders.
We present a procedure to build a single time model for the equations of motion of relativistic retarded systems composed of several particles; at any desired level of accuracy. We treat the especial case of a binary system. We apply this model to the classical electromagnetic binary particle system. We mentioned some differences with previous approaches and discussed the implications for linear gravitational models.
We present new results on gravitational lensing over a cosmological Robertson-Walker backgrounds which extend and generalize previous works. Our expressions show the presence of new terms and factors which have been neglected in the literature on the subject. The new equations derived here for the optcal scalars allow to deal with more general matter content including sources with non Newtonian components of the energy-momentum tensor and arbitrary motion. Our treatment is within the framework of weak gravitational lenses in which first order effects of the curvature are considered. We have been able to make all calculations without referring to the concept of deviation angle. This in turn, makes the presentation shorter but also allows for the consideration of global effects on the Robertson-Walker background that have been neglected in the literature. We also discuss two intensity magnification, that we define in this article; one coming from a natural geometrical contruction in terms of the affine distance, that here we call $\tildeμ$, and the other adapted to cosmological discussions in terms of the redshift, that we call $μ'$. We show that the natural intensity magnification $\tildeμ$ coincides with the standard solid angle magnification ($μ$).
We present a class of general prolate and oblate spheroidal spacetimes for the description of cosmic structures in the Universe. They are exact geometries which represent, in an appropriated way, the imbedding of spheroidal matter-energy distributions within a standard cosmological scenario, and therefore they allow for an improved description of a wider class of astrophysical systems from a more accurate point of view. These spacetimes can be used to describe overdensity or underdensity regions; in this work we consider the last case, that is, the description of cosmic voids. We introduce and study a model of void which is a generalization of a simpler one in spherical symmetry and we use it for the calculation of weak lensing optical scalars as a non-trivial and interesting application. In this particular example we show the rich observable features that can be found in such models.
We present a definition of tensor fields which are average of tensors over a manifold, with a straightforward and natural definition of derivative for the averaged fields; which in turn makes a suitable and practical construction for the study of averages of tensor fields that satisfy differential equations. Although we have in mind applications to general relativity, our presentation is applicable to a general n-dimensional manifold. The definition is based on the integration of scalars constructed from a physically motivated basis, making use of the least amount of geometrical structure. We also present definitions of covariant derivative of the averaged tensors and Lie derivative.
Here, we present a new definition of {intrinsic angular momentum} at future null infinity, based on the charge-integral approach. This definition is suitable for the general case of radiating spacetimes without symmetries, which does not suffer from supertranslations ambiguities. In the case of axial symmetry this new definition agrees with the Komar integral.