Atomic X-ray Spectroscopy of Accreting Black Holes

Current astrophysical research suggests that the most persistently luminous objects in the Universe are powered by the flow of matter through accretion disks onto black holes. Accretion disk systems are observed to emit copious radiation across the electromagnetic spectrum, each energy band providing access to rather distinct regimes of physical conditions and geometric scale. X-ray emission probes the innermost regions of the accretion disk, where relativistic effects prevail. While this has been known for decades, it also has been acknowledged that inferring physical conditions in the relativistic regime from the behavior of the X-ray continuum is problematic and not satisfactorily constraining. With the discovery in the 1990s of iron X-ray lines bearing signatures of relativistic distortion came the hope that such emission would more firmly constrain models of disk accretion near black holes, as well as provide observational criteria by which to test general relativity in the strong field limit. Here we provide an introduction to this phenomenon. While the presentation is intended to be primarily tutorial in nature, we aim also to acquaint the reader with trends in current research. To achieve these ends, we present the basic applications of general relativity that pertain to X-ray spectroscopic observations of black hole accretion disk systems, focusing on the Schwarzschild and Kerr solutions to the Einstein field equations. To this we add treatments of the fundamental concepts associated with the theoretical and modeling aspects of accretion disks, as well as relevant topics from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian Journal of Physics, in pres

Accretion, Outflows, and Winds of Magnetized Stars

Many types of stars have strong magnetic fields that can dynamically influence the flow of circumstellar matter. In stars with accretion disks, the stellar magnetic field can truncate the inner disk and determine the paths that matter can take to flow onto the star. These paths are different in stars with different magnetospheres and periods of rotation. External field lines of the magnetosphere may inflate and produce favorable conditions for outflows from the disk-magnetosphere boundary. Outflows can be particularly strong in the propeller regime, wherein a star rotates more rapidly than the inner disk. Outflows may also form at the disk-magnetosphere boundary of slowly rotating stars, if the magnetosphere is compressed by the accreting matter. In isolated, strongly magnetized stars, the magnetic field can influence formation and/or propagation of stellar wind outflows. Winds from low-mass, solar-type stars may be either thermally or magnetically driven, while winds from massive, luminous O and B type stars are radiatively driven. In all of these cases, the magnetic field influences matter flow from the stars and determines many observational properties. In this chapter we review recent studies of accretion, outflows, and winds of magnetized stars with a focus on three main topics: (1) accretion onto magnetized stars; (2) outflows from the disk-magnetosphere boundary; and (3) winds from isolated massive magnetized stars. We show results obtained from global magnetohydrodynamic simulations and, in a number of cases compare global simulations with observations.Comment: 60 pages, 44 figure

General Relativistic MHD Jets

Magnetic fields connecting the immediate environs of rotating black holes to large distances appear to be the most promising mechanism for launching relativistic jets, an idea first developed by Blandford and Znajek in the mid-1970s. To enable an understanding of this process, we provide a brief introduction to dynamics and electromagnetism in the spacetime near black holes. We then present a brief summary of the classical Blandford-Znajek mechanism and its conceptual foundations. Recently, it has become possible to study these effects in much greater detail using numerical simulation. After discussing which aspects of the problem can be handled well by numerical means and which aspects remain beyond the grasp of such methods, we summarize their results so far. Simulations have confirmed that processes akin to the classical Blandford-Znajek mechanism can launch powerful electromagnetically-dominated jets, and have shown how the jet luminosity can be related to black hole spin and concurrent accretion rate. However, they have also shown that the luminosity and variability of jets can depend strongly on magnetic field geometry. We close with a discussion of several important open questions.Comment: 21 pages, 2 figures, To appear in Belloni, T. (ed.): The Jet Paradigm - From Microquasars to Quasars, Lect. Notes Phys. 794 (2009

Origin and Evolution of Saturn's Ring System

The origin and long-term evolution of Saturn's rings is still an unsolved problem in modern planetary science. In this chapter we review the current state of our knowledge on this long-standing question for the main rings (A, Cassini Division, B, C), the F Ring, and the diffuse rings (E and G). During the Voyager era, models of evolutionary processes affecting the rings on long time scales (erosion, viscous spreading, accretion, ballistic transport, etc.) had suggested that Saturn's rings are not older than 100 My. In addition, Saturn's large system of diffuse rings has been thought to be the result of material loss from one or more of Saturn's satellites. In the Cassini era, high spatial and spectral resolution data have allowed progress to be made on some of these questions. Discoveries such as the ''propellers'' in the A ring, the shape of ring-embedded moonlets, the clumps in the F Ring, and Enceladus' plume provide new constraints on evolutionary processes in Saturn's rings. At the same time, advances in numerical simulations over the last 20 years have opened the way to realistic models of the rings's fine scale structure, and progress in our understanding of the formation of the Solar System provides a better-defined historical context in which to understand ring formation. All these elements have important implications for the origin and long-term evolution of Saturn's rings. They strengthen the idea that Saturn's rings are very dynamical and rapidly evolving, while new arguments suggest that the rings could be older than previously believed, provided that they are regularly renewed. Key evolutionary processes, timescales and possible scenarios for the rings's origin are reviewed in the light of tComment: Chapter 17 of the book ''Saturn After Cassini-Huygens'' Saturn from Cassini-Huygens, Dougherty, M.K.; Esposito, L.W.; Krimigis, S.M. (Ed.) (2009) 537-57

Orientation of Galaxies in the Local Supercluster: A Review

The progress of the studies on the orientation of galaxies in the Local Supercluster (LSC) is reviewed and a summary of recent results is given. Following a brief introduction of the LSC, we describe the results of early studies based on two-dimensional analysis, which were mostly not conclusive. We describe next the three-dimensional analysis, which is used widely today. Difficulties and systematic effects are explained and the importance of selection effects is described. Then, results based on the new method and modern databases are given, which are summarized as follows. When the LSC is seen as a whole, galaxy planes tend to align perpendicular to the LSC plane with lenticulars showing the most pronounced tendency. Projections onto the LSC plane of the spin vectors of Virgo cluster member galaxies, and to some extent, those of the total LSC galaxies, tend to point to the Virgo cluster center. This tendency is more pronounced for lenticulars than for spirals. It is suggested that 'field' galaxies, i.e., those which do not belong to groups with more than three members, may be better objects than other galaxies to probe the information at the early epoch of the LSC formation through the analysis of galaxy orientations. Field lenticulars show a pronounced anisotropic distribution of spin vectors in the sense that they lay their spin vectors parallel to the LSC plane while field spirals show an isotropic spin-vector distribution.Comment: 21 pages, 10 figures; Accepted for publication in Astrophysics and Space Scienc

General Overview of Black Hole Accretion Theory

I provide a broad overview of the basic theoretical paradigms of black hole accretion flows. Models that make contact with observations continue to be mostly based on the four decade old alpha stress prescription of Shakura & Sunyaev (1973), and I discuss the properties of both radiatively efficient and inefficient models, including their local properties, their expected stability to secular perturbations, and how they might be tied together in global flow geometries. The alpha stress is a prescription for turbulence, for which the only existing plausible candidate is that which develops from the magnetorotational instability (MRI). I therefore also review what is currently known about the local properties of such turbulence, and the physical issues that have been elucidated and that remain uncertain that are relevant for the various alpha-based black hole accretion flow models.Comment: To be published in Space Science Reviews and as hard cover in the Space Sciences Series of ISSI: The Physics of Accretion on to Black Holes (Springer Publisher

State of nature 2019

State of Nature 2019 presents an overview of how the country’s wildlife is faring, looking back over nearly 50 years of monitoring to see how nature has changed in the UK, its Crown Dependencies and Overseas Territories. As well as this long-term view, we focus on what has happened in the last decade, and so whether things are getting better or worse for nature. In addition, we have assessed the pressures that are acting on nature, and the responses being made, collectively, to counter these pressures

Associations between diabetes and sex with peritoneal dialysis technique and patient survival: Results from the Australia and New Zealand Dialysis and Transplant Registry cohort study

First Published April 22, 2020BACKGROUND:A differential association between mortality and cause of end-stage kidney disease in patients with type 2 diabetes mellitus (T2DM) has been shown. Sex-specific differences in diabetes-related complications have been described. It is unclear whether sex affects the associations between diabetes and peritoneal dialysis (PD) technique and patient survival. METHODS:Using the Australia and New Zealand Dialysis and Transplant Registry, we examined a two-way interaction between sex and diabetes status (no diabetes, T2DM and non-diabetic nephropathy [T2DM + non-DN] and T2DM and diabetic nephropathy [T2DM + DN]) for PD technique failure (including death), all-cause mortality and cause-specific mortality in incident adult PD patients between 1996 and 2016 using adjusted Cox regression. Mediation analysis was conducted to determine whether peritonitis was a mediator in these associations. RESULTS:In 8279 PD patients, those with T2DM + DN had the greatest risks in technique failure, all-cause mortality and cause-specific mortality followed by patients with T2DM + non-DN, then patients without diabetes. Sex modified the association with diabetes status in technique failure (p interaction = 0.001) and cardiac mortality (p interaction = 0.008). In women with T2DM + DN, the adjusted hazard ratio (HR) for technique failure was 1.45 (1.30-1.62) and was higher than men with T2DM + DN (1.17 [1.08-1.28]; referent: no diabetes). In women with T2DM + DN, the adjusted HR for cardiac mortality was 2.12 (1.73-2.61) and was also higher than men with T2DM + DN (1.66 [1.43-1.95]). Less than 10 % of the effect between diabetes and PD technique failure or mortality was mediated by peritonitis. CONCLUSIONS:PD patients with diabetic nephropathy had increased risk of PD technique failure and mortality, with the magnitude of these risks greater in women.Jenny HC Chen, David W Johnson, Germaine Won

Capturing lay perspectives in a randomized control trial of a health promotion intervention for people with osteoarthritis of the knee

Osteoarthritis (OA) is a common and often disabling condition that predominately affects older adults. It is the commonest cause of locomotor disability and forms a major element of the workload in primary care. Previous studies suggest that there are both deficits in the knowledge patients have about their disease and extensive 'unmet' information needs. This paper explores the patients' perspective on the meaning and significance of living with arthritis, identified through quantitative and qualitative approaches undertaken during a trial that evaluated the effectiveness of a primary care-based patient education programme. This paper draws on qualitative and quantitative data from: the baseline interview (knowledge of arthritis, satisfaction with services and support received in primary care); patient diaries (individual goals and reflections on treatment); and group teaching sessions (themes describing the patient's experience). The different data sources were interrogated for common and divergent themes. One hundred and ninety-four participants were identified and 170 completed baseline interviews. Participants were predominantly female (73%), with a mean age of 63 and arthritis of long-standing; 55% reported that they had had it for 5 years or more. Use of primary care services was high, with 41% consulting their GP in the 2 weeks before interview. Levels of information were low, with less than 25% receiving support/advice about the disease, pain management or its impact upon daily life. Set against negative perceptions of the quality of services, patients' personal priorities were for improved pain management and enhanced mobility/functional ability. The combined quantitative and qualitative data provide insight into the patients' perspective on the causes and impact of knee OA, individual goals desired from treatment and the quality of care. There is consistent evidence of unmet needs for information and support and the priority placed by patients on finding strategies to cope with OA and maintaining independence. Even within a tightly defined study sample participating in the intervention, a diversity of experience and goals were revealed, which highlights the importance of taking account of contextual factors and individual differences when evaluating complex interventions