7 research outputs found
Testing the nature of black holes with gravitational waves
No full textWhat is the nature of the dark, massive ultracompact objects that populate our Universe? This question is the guiding line for the work developed in this thesis. Black holes are an extremely successful model to describe these compact objects and are supported by a solid theoretical foundation and consistent with all astrophysical observations. However, black holes have several theoretical problems that are not fully understood and could potentially be an issue for the self-consistency of General Relativity. One way to evade their outstanding issues is to consider that some new physics prevents the full collapse to a black hole and an exotic compact object is formed. Quantifying the evidence for horizons is, therefore, an essential and pressing task in future gravitational-wave observations. In this thesis, we investigate a wide variety of phenomenological effects of exotic compact objects and put them to test against the behavior of black holes. Some particularly relevant quantities that we study here are the multipole moments of the object, which may differ significantly from those of black holes and provide a good way to test the nature of compact objects in a binary. We study in particular the multipole moments of (i) fuzzballs - a multicenter microstate geometry arising from string theory - finding that the multipolar structure is much richer than Kerr and can be used to put constraints on these models with future gravitational wave observations; (ii) soft" exotic compact objects - for which the curvature at the surface is comparable with the corresponding curvature at the horizon, and finding that the multipole moments that are not spin-induced are strongly suppressed in the black-hole limit suggesting that their detection is challenging but possibly feasible with next-generation gravitational-wave detectors; (iii) neutron stars with quadrupolar deformations, where the latter is induced by an anisotropic crust (modeled by a thin shell), finding indications that a more complete of study of elastic properties of neutron stars may be required to understand the gravitational-wave signatures of coalescing neutron-star binaries. We also considered a particular model of an exotic compact object with self-gravitating anisotropic matter, where we developed the first fully covariant study for this type of object. We find that anisotropic stars have interesting phenomenological signatures, such as tidal Love numbers and gravitational echoes, and can evade some of the most pressing challenges that other exotic compact objects face when attempting to mimic the black hole model. The fully covariant framework suggest that these objects may be used to study numerically the behavior of ultracompact objects
Exotic compact objects with soft hair
No full textMotivated by the lack of a general parametrization for exotic compact objects, we construct a class of perturbative solutions valid for small (but otherwise generic) multipolar deviations from a Schwarzschild metric in general relativity. We introduce two classes of exotic compact objects, with "soft" and "hard" hair, for which the curvature at the surface is respectively comparable to or much larger than that at the corresponding black-hole horizon. We extend the Hartle-Thorne formalism to relax the assumption of equatorial symmetry and to include deformations induced by multipole moments higher than the spin, thus constructing the most general, axisymmetric quasi-Schwarzschild solution to Einstein's vacuum equations. We explicitly construct several particular solutions of objects with soft hair, which might be useful for tests of quasiblack-hole metrics, and also to study deformed neutron stars. We show that the more compact a soft exotic object is, the less hairy it will be. All its multipole moments can approach their corresponding Kerr values only in two ways as their compactness increases: either logarithmically (or faster) if the moments are spin-induced, or linearly (or faster) otherwise. Our results suggest that it is challenging (but possibly feasible with next-generation gravitational-wave detectors) to distinguish Kerr black holes from a large class of ultracompact exotic objects on the basis of their different multipolar structure
Testing strong-field gravity with tidal Love numbers
No full textThe tidal Love numbers (TLNs) encode the deformability of a self-gravitating object immersed in a tidal environment and depend significantly both on the object's internal structure and on the dynamics of the gravitational field. An intriguing result in classical general relativity is the vanishing of the TLNs of black holes. We extend this result in three ways, aiming at testing the nature of compact objects: (i) we compute the TLNs of exotic compact objects, including different families of boson stars, gravastars, wormholes, and other toy models for quantum corrections at the horizon scale. In the black-hole limit, we find a universal logarithmic dependence of the TLNs on the location of the surface. (ii) We compute the TLNs of black holes beyond vacuum general relativity, including Einstein-Maxwell, Brans-Dicke, and Chern-Simons gravity. (iii) We assess the ability of present and future gravitational-wave detectors to measure the TLNs of these objects, including the first analysis of TLNs with LISA. Both LIGO, ET, and LISA can impose interesting constraints on boson stars, while LISA is able to probe even extremely compact objects. We argue that the TLNs provide a smoking gun of new physics at the horizon scale and that future gravitational-wave measurements of the TLNs in a binary inspiral provide a novel way to test black holes and general relativity in the strong-field regime
Black-hole microstate spectroscopy: Ringdown, quasinormal modes, and echoes
No full textDeep conceptual problems associated with classical black holes can be addressed in string theory by the "fuzzball" paradigm, which provides a microscopic description of a black hole in terms of a thermodynamically large number of regular, horizonless, geometries with much less symmetry than the corresponding black hole. Motivated by the tantalizing possibility to observe quantum gravity signatures near astrophysical compact objects in this scenario, we perform the first 3 + 1 numerical simulations of a scalar field propagating on a large class of multicenter geometries with no spatial isometries arising from N = 2 four-dimensional supergravity. We identify the prompt response to the perturbation and the ringdown modes associated with the photon sphere, which are similar to the black-hole case, and the appearance of echoes at later time, which is a smoking gun of some structure at the horizon scale and of the regular interior of these solutions. The response is in agreement with an analytical model based on geodesic motion in these complicated geometries. Our results provide the first numerical evidence for the dynamical linear stability of fuzzballs, and pave the way for an accurate discrimination between fuzzballs and black holes using gravitational-wave spectroscopy
Armazém da província: vida literária e sociabilidades intelectuais em Florianópolis na primeira república
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Filosofia e Ciências Humanas, Programa de Pós-Graduação em História, Florianópolis, 2014.O presente trabalho discute o campo cultural de Florianópolis durante a Primeira República, com ênfase em sua elite literária, a chamada "Geração da Academia", investigando as relações entre práticas sociais, construções intelectuais e o peso dos pertencimentos sociais em seu repertório de ações. Para isto, reconstroem-se as trajetórias sociais dos membros desta elite literária, seus laços de sociabilidades, suas instâncias de consagração, seus projetos editorias com ênfase no periodismo, as relações que mantiveram com grupos adversários e as demais práticas sociais que estabeleceram em suas batalhas por distinção, legitimação, espaços e capitais dentro de um campo cultural subordinado ao Partido Republicano Catarinense. Busca-se repensar velhos modelos de análise do campo cultural e da experiência literária na cidade restituindo a complexidade do que ficou encoberto pelas representações e discursos elaborados sobre o período, em especial pelo cânone modernista, compreendendo as sobreposições ideológicas que revestem os discursos sobre o campo cultural.Abstract : This doctorate thesis discusses the cultural field in Florianopolis during the First Republic, with emphasis on its literary elite, the so-called "Academy´s Generation", investigating the relationship between social practices, intellectual constructs and the weight of social affiliations in their repertoire of actions. For this, rebuild up the social trajectories of the members of this literary elite, their bonds of sociability, their instances of consecration, his editorial projects with an emphasis on journalism and magazines, the relations that maintained with opposing groups and other social practices that have established in their battles by distinction, legitimacy, spaces and capital within a cross cultural field to the Republican Party. The goal is to rethink old models of analysis of literary and cultural field experience in the city restoring the complexity of what was covered up by the representations and elaborate discourses on the period, especially by the modernist canon, comprising the ideological overlays that cover the discourses on the cultural field
A gestão universitária de projetos de extensão na perspectiva da gestão social
No full textDissertação (mestrado profissional) - Universidade Federal de Santa Catarina, Centro Sócio-Econômico, Programa de Pós-Graduação em Administração Universitária, Florianópolis, 2013A presente dissertação, ao realizar um estudo de caso para pesquisar a gestão universitária de Projetos de Extensão, teve por objetivo geral: "Propor alternativas para que a Gestão Universitária dos Projetos de Extensão do CSE/UFSC possa produzir resultados na perspectiva da Gestão Social". O estudo realizou uma pesquisa aplicada, qualitativa, descritiva, pesquisa bibliográfica e documental, com levantamento de campo. Foram conceituadas e utilizadas as categorias: Administração Pública e Gestão Universitária; Gestão Estratégica e Gestão Social. Os resultados apontaram que: i) as instâncias deliberativas e a legislação da UFSC e do CSE configuram a gestão da Extensão Universitária com estruturas e operacionalização fundamentadas na racionalidade burocrática e valores normativos, processo decisório e comunicação verticalizados e monológicos, autonomia e poder centralizados, atendendo, na maior parte, aos interesses da Universidade, em detrimento do interesse coletivo de caráter público; ii) as competências do CSE, o Regimento do CSE e o Sistema de Registro de Ações de Extensão (SIRAEx) confirmam uma administração da Extensão Universitária nos padrões da Gestão Pública, típicas da esfera pública estatal, sem contemplar as características da Gestão Social; iii) a legislação federal e as recomendações dos FORPROEX estabelecem, em parte, diretrizes para a prática da educação superior e da Extensão Universitária pautadas nos princípios da Gestão Social. Conclui-se que: i) há dissonância entre o modelo de Extensão Universitária regulado pela legislação federal, o processo de gestão de Extensão Universitária do CSE/UFSC e a avaliação apresentada nos questionários pelos gestores, chefias e coordenadores de extensão do CSE; ii) a gestão da Extensão Universitária do CSE/UFSC configura-se como Administração Pública Gerencial (PAES DE PAULA, 2005) ou Gestão Pública (PIMENTEL; PIMENTEL, 2010); iii) há oportunidade aberta para que o CSE/UFSC possa realizar a inovação social, integrando ensino, pesquisa e extensão, promovendo parcerias entre Universidade e Sociedade civil organizada, ampliando seu papel de empreendedor social e sua contribuição a serviço da cidadania e do desenvolvimento sustentável. Finalmente, o estudo alinha alternativas que podem ser úteis ao CSE/UFSC no processo de revisão e redesenho da Gestão Universitária dos Projetos de Extensão, de modo a incorporar inovação social substantiva à luz da Gestão Social.Abstract : As this thesis executes a case study to research the management of university extension projects the general purpose is "Propose alternatives so that University Management to the CSE/UFSC Extension Projects can produce results in the perspective of Social Management". The study did an applied research, qualitative, descriptive, bibliographic and documentary research, with field survey. Was been conceptualized and used the categories: Public Administration and University Management; Strategic Management and Social Management. The results showed that: i) the deliberative instances and legislation of UFSC and CSE configure the management structures and university extension with the structure and operationalization based on bureaucratic rationality and normative values, decision-making process and communication vertical and monological, autonomy and centralized power, serving mostly the interests of the university, against the collective interest; ii) the duties of CSE, the CSE regiments and the Registration System from Actions of Extension (SIRAEx) confirm one administration of university extension in patterns of Public Management, typical of the social public sphere, without considering the characteristics of Social Management; iii) federal legislation and the recommendations of FORPROEX establish, in part, guidelines for the practice of higher education and university extension based on the principles of Social Management. It is concluded that: i) there is dissonance between the model of university extension regulated by federal law, the process of management of university extension from CSE/UFSC and evaluation presented in the questionnaires by managers, supervisors and coordinators of CSE extension; ii) the management of university extension CSE/UFSC configured as Public Administration Management (PAES DE PAULA, 2005) or Public Management (PIMENTEL; PIMENTEL, 2010); iii) there is an opportunity to the CSE/UFSC can realize a social innovation, integrating education, research and extension, promoting partnerships between the university and civil society, expanding their role as a social enterprising and their contribution in the service of citizenship and sustainable development. Finally, the study aligns alternatives that may be useful to CSE/UFSC in the process of revision and redesign of University Management for the Project Extension, to incorporate the social innovation substantive to the light of Social Management
Black holes, gravitational waves and fundamental physics: a roadmap
No full textWhite Paper for the COST action "Gravitational Waves, Black Holes, and Fundamental Physics", 272 pages, 12 figures; v4: updated references and author list. Overall improvements and corrections. To appear in Classical and Quantum GravityInternational audienceThe grand challenges of contemporary fundamental physics—dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem—all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on ‘Black holes, Gravitational waves and Fundamental Physics’
