Retaining Black Holes with Very Large Recoil Velocities

Recent numerical simulations of binary black hole mergers show the possibility of producing very large recoil velocities (> 3000 km/s). Kicks of this magnitude should be sufficient to eject the final black hole from virtually any galactic potential. This result has been seen as a potential contradiction with observations of supermassive black holes residing in the centers of most galaxies in the local universe. Using an extremely simplified merger tree model, we show that, even in the limit of very large ejection probability, after a small number of merger generations there should still be an appreciable fraction (>50%) of galaxies with supermassive black holes today. We go on to argue that the inclusion of more realistic physics ingredients in the merger model should systematically increase this retention fraction, helping to resolve a potential conflict between theory and observation. Lastly, we develop a more realistic Monte Carlo model to confirm the qualitative arguments and estimate occupation fractions as a function of the central galactic velocity dispersion.Comment: 6 pages, 3 figures; Comments welcom

Gravitational recoil from spinning binary black hole mergers

The inspiral and merger of binary black holes will likely involve black holes with both unequal masses and arbitrary spins. The gravitational radiation emitted by these binaries will carry angular as well as linear momentum. A net flux of emitted linear momentum implies that the black hole produced by the merger will experience a recoil or kick. Previous studies have focused on the recoil velocity from unequal mass, non-spinning binaries. We present results from simulations of equal mass but spinning black hole binaries and show how a significant gravitational recoil can also be obtained in these situations. We consider the case of black holes with opposite spins of magnitude $a$ aligned/anti-aligned with the orbital angular momentum, with $a$ the dimensionless spin parameters of the individual holes. For the initial setups under consideration, we find a recoil velocity of V = 475 \KMS a. Supermassive black hole mergers producing kicks of this magnitude could result in the ejection from the cores of dwarf galaxies of the final hole produced by the collision.Comment: 8 pages, 8 figures, replaced with version accepted for publication in Ap

The Assembly and Merging History of Supermassive Black Holes in Hierarchical Models of Galaxy Formation

We assess models for the assembly of supermassive black holes (SMBHs) at the center of galaxies that trace their hierarchical build-up far up in the dark halo `merger tree'. We assume that the first `seed' black holes (BHs) formed in (mini)halos collapsing at z=20 from high-sigma density fluctuations. As these pregalactic holes become incorporated through a series of mergers into larger and larger halos, they sink to the center owing to dynamical friction, accrete a fraction of the gas in the merger remnant to become supermassive, form a binary system, and eventually coalesce. The merger history of dark matter halos and associated BHs is followed by cosmological Monte Carlo realizations of the merger hierarchy. A simple model, where quasar activity is driven by major mergers and SMBHs accrete at the Eddington rate a mass that scales with the fifth power of the velocity dispersion, is shown to reproduce the optical LF of quasars in the redshift range 1<z<4. Binary and triple BH interactions are followed in our merger tree. The assumptions underlying our scenario lead to the prediction of a population of massive BHs wandering in galaxy halos and the intergalactic medium at the present epoch, and contributing <10% to the total BH mass density. At all epochs the fraction of binary SMBHs in galaxy nuclei is of order 10%, while the fraction of binary quasars is less than 0.3%Comment: revised version, accepted for publication in the ApJ, emulateapj, 15 pages, 16 figure

Climate change threats to two low-lying South African coastal towns: Risks and perceptions.

Climate change poses a considerable threat to low-lying coastal towns. Possible risks include flooding induced by sea-level rise, increased discomfort from changes in temperature and precipitation, more frequent extreme events, biodiversity shifts, and water shortages. For coastal towns that attract many tourists, these threats can have far-reaching economic effects and may compromise the continued viability of the tourism sector. A growing number of studies are being published on the inter-relationship between climate change and tourism in the global North. As yet, little equivalent research has been conducted in developing countries with economically significant tourism sectors. This paper presents a mixed-method pilot study on two adjacent coastal towns, St Francis Bay and Cape St Francis, in the Eastern Cape Province of South Africa. We explored the climate change threats in this region, and perceptions of these threats within the tourism sector. The tourism climate index results showed that the towns are climatically well suited to tourism, but a decrease in these index scores between 1978 and 2014 suggests that climate change experienced in recent decades has detrimentally affected tourist comfort. A digital elevation model sea-level projection for the towns indicated a high risk of sea-level induced flooding by 2050, particularly for properties along the coastline. Interviews with tourism establishment respondents showed that people are aware of climate change threats, yet little adaptation is forthcoming. Rather the government is deemed responsible for adaptation, despite its limited capacity. A disjuncture therefore exists between the perceived severity of risk and the risk that is evident from scientific analyses. This gap results in poor planning for the costs associated with adaptation.NCS201

The Infrared Afterglow of Supermassive Black Hole Mergers

We model the spectra and light curves of circumbinary accretion disks during the time after the central black holes merge. The most immediate effect of this merger is the dissipation of energy in the outer regions of the disk due to the gravitational wave energy and linear momentum flux released at merger. This has the effect of perturbing the gas in the disk, which then radiates the dissipated energy over a cooling timescale, giving a characteristic infrared signal for tens of thousands of years when the total black hole mass is M~10^8 M_sun. On the basis of a simple cosmological merger model in which a typical supermassive black hole undergoes a few major mergers during its lifetime, we predict that ~10^4-10^5 of these IR sources should be observable today and discuss the possibility of identifying them with multi-wavelength surveys such as SWIRE/XMM-LSS/XBootes and COSMOS.Comment: v2: expanded discussion of optical depth calculations; ApJ in pres

Recoiling Black Holes in Quasars

Recent simulations of merging black holes with spin give recoil velocities from gravitational radiation up to several thousand km/s. A recoiling supermassive black hole can retain the inner part of its accretion disk, providing fuel for a continuing QSO phase lasting millions of years as the hole moves away from the galactic nucleus. One possible observational manifestation of a recoiling accretion disk is in QSO emission lines shifted in velocity from the host galaxy. We have examined QSOs from the Sloan Digital Sky Survey with broad emission lines substantially shifted relative to the narrow lines. We find no convincing evidence for recoiling black holes carrying accretion disks. We place an upper limit on the incidence of recoiling black holes in QSOs of 4% for kicks greater than 500 km/s and 0.35% for kicks greater than 1000 km/s line-of-sight velocity.Comment: 4 pages, 4 figures, uses emulateapj, Submitted to ApJ Letter

Recoiling from a kick in the head-on collision of spinning black holes

Recoil ``kicks'' induced by gravitational radiation are expected in the inspiral and merger of black holes. Recently the numerical relativity community has begun to measure the significant kicks found when both unequal masses and spins are considered. Because understanding the cause and magnitude of each component of this kick may be complicated in inspiral simulations, we consider these effects in the context of a simple test problem. We study recoils from collisions of binaries with initially head-on trajectories, starting with the simplest case of equal masses with no spin and then adding spin and varying the mass ratio, both separately and jointly. We find spin-induced recoils to be significant relative to unequal-mass recoils even in head-on configurations. Additionally, it appears that the scaling of transverse kicks with spins is consistent with post-Newtonian theory, even though the kick is generated in the nonlinear merger interaction, where post-Newtonian theory should not apply. This suggests that a simple heuristic description might be effective in the estimation of spin-kicks.Comment: 12 pages, 10 figures. Replaced with published version, including more discussion of convergence and properties of final hol

Uma análise dos preditores do conhecimento do conteúdo da história: Implicações para política e prática

How and to what extent students learn history content is a complicated process, drawing from the instructional opportunities they experience; the policy prioritization of history/social studies instruction in schools; and their own cultural perspectives toward the past. In an attempt to better understand the complex inter-play among these dimensions, we examined relationships among student sociocultural characteristics, instructional exposure, and school-level variables and US History content knowledge. Using data from the 2010 National Assessment of Educational Progress Test on US History (NAEP-USH), multilevel analyses indicated that while sociocultural indicators (such as race, gender, and socioeconomic status) correlate with achievement, students’ instructional exposure variables remain significant predictors of history content knowledge. Moreover, school context such as building-level demographics and state testing-policy predict between school variance in content knowledge and moderate the achievement gap. Results also suggest that, while a substantial achievement gap remains, exposure to text-based instructional practices is associated with increased knowledge. Findings from this study have policy implications for the development of a more inclusive social studies curriculum, the advocating of text-dependent instruction as a high-leverage practice among history teachers, and cautious consideration of tests as proxies for accountability in history education. Entender cómo y cuántos alumnos aprenden sobre contenido histórico es un proceso complicado, basado en oportunidades de aprendizaje que los alumnos encuentran, en una política de priorización de la enseñanza de contenido histórico o de ciencias sociales, y en las perspectivas culturales de los alumnos sobre el estudio del pasado. Con el objetivo de entender la relación compleja entre los diversos aspectos en este proceso de aprendizaje, investigamos la relación entre características socioculturales de los alumnos, acceso a este tipo de enseñanza, y variables explicativas de escuelas y del conocimiento de la historia de los Estados Unidos. El resultado de nuestra modelación jerárquica indica que mientras variables socioculturales (raza, sexo y situación socioeconómica) se correlacionan con éxito, con datos de la Evaluación Nacional de la Prueba de Progreso Educativo en Historia Americana (NAEP-USH, por sus siglas en inglés) Académico, las variables de acceso a este tipo de enseñanza son parámetros importantes para el conocimiento del contenido histórico. Además, variables sobre la escuela, por ejemplo demografía de la escuela y políticas estaduales en cuanto a pruebas académicas, son parámetros relevantes en el análisis de varianza en conocimiento sobre el contenido académico y la disparidad en éxito académico entre alumnos. Los resultados también indican que a pesar de la existencia de la disparidad en el éxito académico, el acceso a textos y materiales educativos está relacionado con el avance del conocimiento. Nuestras conclusiones son relevantes para el desarrollo de políticas educativas de un currículo en ciencias sociales que sea más inclusivo, el apoyo al uso de instrucciones usando textos / libros académicos, y la cautela en cuanto al uso de pruebas para medir la enseñanza de la historia. Entender como e o quanto alunos aprendem sobre conteúdo histórico é um processo complicado, baseado em oportunidades de aprendizagem que alunos encontram, numa política de priorização do ensino de conteúdo histórico ou de ciências sociais, e nas perspectivas culturais dos alunos sobre o estudo do passado. Com o objetivo de entender a relação complexa entre os vários aspectos neste processo de aprendizagem,  nós investigamos a relação entre características socioculturais dos alunos, acesso a este tipo de ensino, e variáveis explanatórias de escolas e do conhecimento da história dos EUA. Usando dados da Avaliação Nacional do Teste de Progresso Educacional em História Americana (NAEP-USH, por sua sigla em inglês) de 2010, os resultados da nossa modelação hierárquica indicam que enquanto variáveis socioculturais (raça, sexo e situação socioeconômica) são correlacionadas com sucesso acadêmico, variáveis de acesso a este tipo de ensino são parâmetros importantes para o conhecimento de conteúdo histórico. Além disso, variáveis sobre a escola, por exemplo demografia da escola e políticas estaduais quanto a testes acadêmicos, são parâmetros relevantes na análise de variância em conhecimento sobre o conteúdo acadêmico e a disparidade em sucesso acadêmico entre alunos. Os resultados também indicam que apesar da existência da disparidade em sucesso acadêmico, acesso a textos e materiais  educativos é relacionado com o avanço de conhecimento. Nossas conclusões são relevantes para o desenvolvimento de políticas educacionais de um currículo em ciências sociais que seja mais inclusivo, o apoio ao uso de instruções usando textos/ livros acadêmicos, e a cautela quanto ao uso de provas para medir o ensino de história.

Systematic analysis of funding awarded for norovirus research to institutions in the United Kingdom, 1997-2010

Objectives:Norovirus infections pose great economic and disease burden to health systems around the world. This study quantifies the investments in norovirus research awarded to UK institutions over a 14-year time period.Design:A systematic analysis of public and philanthropic infectious disease research investments awarded to UK institutions between 1997 and 2010.Participants:NoneSetting:UK institutions carrying out infectious disease research.Main outcome measures:Total funding for infectious disease research, total funding for norovirus research, position of norovirus research along the R&amp;D value chain.Results:The total dataset consisted of 6165 studies with sum funding of £2.6 billion. Twelve norovirus studies were identified with a total funding of £5.1 million, 0.2% of the total dataset. Of these, eight were categorized as pre-clinical, three as intervention studies and one as implementation research. Median funding was £200,620.Conclusions:Research funding for norovirus infections in the UK appears to be unacceptably low, given the burden of disease and disability produced by these infections. There is a clear need for new research initiatives along the R&amp;D value chain: from pre-clinical through to implementation research, including trials to assess cost-effectiveness of infection control policies as well as clinical, public health and environmental interventions in hospitals, congregate settings and in the community.</p

Gravitational Recoil during Binary Black Hole Coalescence using the Effective One Body Approach

Using the Effective One Body approach, that includes nonperturbative resummed estimates for the damping and conservative parts of the compact binary dynamics, we compute the recoil during the late inspiral and the subsequent plunge of non-spinning black holes of comparable masses moving in quasi-circular orbits. Further, using a prescription that smoothly connects the plunge phase to a perturbed single black hole, we obtain an estimate for the total recoil associated with the binary black hole coalescence. We show that the crucial physical feature which determines the magnitude of the terminal recoil is the presence of a ``burst'' of linear momentum flux emitted slightly before coalescence. When using the most natural expression for the linear momentum flux during the plunge, together with a Taylor-expanded $(v/c)^4$ correction factor, we find that the maximum value of the terminal recoil is $\sim 74$ km/s and occurs for a mass ratio $m_2/m_1 \simeq 0.38$. We comment, however, on the fact that the above `best bet estimate' is subject to strong uncertainties because the location and amplitude of the crucial peak of linear momentum flux happens at a moment during the plunge where most of the simplifying analytical assumptions underlying the Effective One Body approach are no longer justified. Changing the analytical way of estimating the linear momentum flux, we find maximum recoils that range between 49 and 172 km/s. (Abridged)Comment: 46 pages, new figures and discussions, to appear in PR