Introduction

Deep surveys

Deep field observations are a suitable observational technique to probe AGN physics. In multi-wavelength campaigns, astronomers select a field in the sky and produce images from several pointings.

Introduction: Mass-estimation methods for active galaxies and quasars

The Hubble Space Telescope has played a key role in our ability to detect supermassive black holes in the centers of nearby galaxies and to determine their mass through its high angular resolution.

Fred hoyle applied his creative genius to an extraordinary range of problems and worked in a variety of genres. His research covered topics from the solar system to the entire universe. Everything interested him: the Sun, stars, interstellar dust, galaxies and cosmology. He even strayed into political and social science, climate change, archaeology, palaeontology and molecular biology. He exploited every medium available – research papers, monographs, science fiction, children's books and textbooks – to get his messages across. Any opportunity to make a radio or television broadcast delighted him, as did giving popular lectures, which attracted huge crowds. Most of the time he worked like a grasshopper in summer, jumping abruptly from one thing to another. In recounting his scientific career, it is inevitable that the narrative must by turns advance and backtrack. Take, for example, his work on accretion, on cosmology and on astrophysics: these all overlap in time, but they are largely disconnected in intellectual terms. For that reason, I have generally chosen to cover one area of research at a time, considering together clusters of related papers and books. We now turn to his investigations on the evolution of stars, which began just before the war and remained an important theme in his work until the mid-1960s.

Most productive scientists today write their papers on a computer. Hoyle's working method was no different from that of scholars the world over before the age of computers: pen and paper.

Introduction

Most of the radiation from luminous accreting black holes is released within the innermost 20 gravitational radii (i.e., 20rg = 20 GM/c2). In such an energetic environment, iron is a major source of x-ray line emission, with strong emission lines in the 6.4–6.9 keV band. Observations of such line emission provides us with a diagnostic of the accretion flow and the behavior of matter and radiation in the strong gravity regime very close to the black hole (Fabian et al. 2000; Reynolds & Nowak 2003; Fabian & Miniutti 2009; Miller 2007).

The rapid x-ray variability found in many Seyfert galaxies is strong evidence for the emission orginating at small radii.

I am often asked if I had a mentor who propelled me towards a life in science. There was no personal mentor as such, but Fred Hoyle, more than anybody, was my role model, and he strongly influenced my career in several ways. I was one of many youngsters deeply influenced by Frontiers of Astronomy, which I read whilst in the Sixth Form at Woodhouse Grammar School in North Finchley. About the same time I was presented at Speech Day with Norton's Star Atlas by our local Member of Parliament, one Margaret Thatcher. These events set me squarely on the path of theoretical astronomy and cosmology.

Fred's science fiction also influenced me. I have vivid memories of the television series A for Andromeda, featuring the ravishing Julie Christie. His masterful book The Black Cloud continues to colour my thinking about the nature of life and consciousness. I was thrilled to discover that a professional scientist could combine fundamental research with fiction writing, bringing to both challenging new concepts and ideas.

The first Hoyle lecture I attended was delivered at the Royal Society in 1967, when I was a beginning PhD student at University College London. Fred spoke about the arrow of time, and the Wheeler-Feynman theory of electrodynamics. I can definitely trace my lifelong interest in the nature of time to this lecture. Indeed, I soon thereafter abandoned my research into atomic astrophysics and took up the problem of providing a quantum description of the Wheeler-Feynman theory for the remainder of my PhD thesis.

Introduction

The M• ~ 4 × 106M⊙ MBH in the GC and the stars around it are the closest and observationally most accessible of such systems (Eisenhauer et al. 2005; Ghez et al. 2005). Observations of the GC thus offer a unique opportunity to study in great detail the effects of the MBH and its extreme environment on star formation, stellar evolution and stellar dynamics, and the interactions of stars and compact remnants with the MBH.

Here the focus is stellar relaxation processes. Relaxation plays an important role in a wide range of phenomena that involve close interactions with an MBH (the “losscone problem,” Section 1.1).

Introduction

Black holes are ‘sighted’ everywhere in the universe these days. Originally located in compact binary x-ray sources in the 1970s, the cosmic presence of black holes has expanded considerably in recent decades. They now are believed to be the central engines that power quasars, active galactic nuclei (AGNs) and gamma-ray bursts (GRBs). They are identified in the cores of all bulge galaxies. They are presumed to form significant populations of compact binaries, including black hole–black hole binaries (BHBHs) and black hole–neutron star binaries (BHNSs). Black holes may even show up soon in the Large Hadron Collider!

Gravitationally, black holes are strong-field objects whose properties are governed by Einstein's theory of relativistic gravitation—general relativity.

Introduction

One of the most important results of the last few years has been the realization that most, if not all, galaxies harbor supermassive black holes (BH) in their centers. The presence of a supermassive BH can manifest itself as luminous quasar “activity,” powered by accretion of matter onto the BH itself. Such a quasar phase, which peaks somewhere around redshift 2, is likely to play an important role in the build-up of these BHs.

Early one morning in October 1933, Fred's mother and father, and his twelve-year-old sister Joan, gave the young scholar a hearty send-off. He began the long journey to Cambridge at Bingley railway station. As the local train chugged along the valley, Hoyle looked back at the forest of mill chimneys clouding the air with smoke. On the hillsides the trees were already showing their autumnal colours. His travelling companions included half a dozen of his classmates from the grammar school. At the first stop, Shipley, they hauled their bags and suitcases to another local train, which brought them to Leeds. Here they bought tickets for the express to Peterborough, about thirty-five miles north of Cambridge. From there a local train clattered across the bleak fenland. Hoyle must have found this flat landscape strikingly different from the moors and dales of Yorkshire. From his window seat he could see farmers ploughing with horses, an extensive drainage system of ditches and dykes, and the fourteenth-century octagon tower of Ely Cathedral soaring over the fens. After some eight hours of travel, Fred and a throng of students descended from the packed train at Cambridge, where they found themselves on the longest railway platform in the country.

The returning undergraduates and the freshers dispersed either to colleges or to lodging houses. Emmanuel College had assigned young Fred a room in a shared house about a mile from both the college and the railway station. Of course, he had no money to spare for a cab.

Since the advent of the Hubble Space Telescope (HST), the progress in studying and understanding black holes has been impressive. Early questions regarding the very existence of black holes have been replaced by questions regarding the role that they play in the formation and evolution of galaxies, particularly at early epochs in the universe. However, the apparently well-established relationship between the mass of the black hole and the mass or luminosity of the galactic bulge rests on a relatively small number of direct observations, and while very few doubt that this relationship exists, it is essential to actually measure the properties of a number of black holes over a range of masses and host galaxies. The direct methods adopted to measure black holes in the nearby universe use gas or stellar kinematics to gather information on the gravitational potential in the nuclear region of the galaxy. The stellar-kinematical method has the advantage that stars are present in all galactic nuclei and their motion is always gravitational. The drawbacks are that it requires relatively long observation times in order to obtain high-quality observations, and that stellar-dynamical models are very complex and potentially plagued by indeterminacy. Conversely, the gas-kinematical method is relatively simple; it requires relatively short observation times for the brightest emission-line nuclei, even if not all galactic nuclei present detectable emission lines. However, an important drawback is that noncircular or non-gravitational motions can completely invalidate this method.

By early 1971, the problem of continuing funding for the Institute of Theoretical Astronomy (IoTA) had become critical. As we have seen, the Nuffield Foundation and the Science Research Council (SRC) had agreed to bear the lion's share of the running costs (80 per cent) until 31 July 1972, at which date it was assumed the University of Cambridge would take full responsibility for the salaries. Of course, there would have to be a limit as to how much the university could afford for the support of astronomy and astrophysics.

From the teaching point of view, the radio astronomers in the Cavendish provided physics lectures and laboratory classes for the natural sciences tripos, while the teaching officers at the Department of Applied Mathematics and Theoretical Physics (DAMTP) carried a large load for the mathematical tripos. The permanent staff of the observatories had graduate students but played no role in undergraduate teaching. This was not due to a lack of willingness on their part but simply reflected the fact that observational astronomers worked at night and in observatories overseas. Most of the Institute staff were on short-term research contracts and therefore were unavailable to support undergraduate teaching, although they had graduate students. In any case, the whole point of founding the Institute had been to free the best minds for research, which is partly why George Batchelor had opposed its foundation in the 1960s.