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Centaurus A (NGC5128) is the nearest active galaxy and one of the first discovered, via its radio and X-ray emission. Although its proximity should make it an ideal test case of the standard model invoking massive black holes, the heavy obscuration due to the dust lane makes it very difficult to study the AGN at high spatial resolution in the optical. Near-infrared observations with HST and with the VLT are now providing high-resolution images and spectra and new insights into the region around the black hole. We summarize what is known about Cen A, discuss the implications of recent HST optical and infrared imaging and polarimetry, and present some preliminary results from VLT/ISAAC. [ABSTRACT FROM AUTHOR]

An empirical relation between ‘canonical' X-ray states in black hole X-ray binaries and radio emission is presented. In the Low/Hard state a quasi-continuous radio-emitting jet is produced. In the High/Soft state the jet is not observed. In the Very High state and at major state transitions, which may correspond physically to rapid and/or significant changes in the inner accretion-disc radius, discrete ejection events, which manifest themselves as radio flares, are observed. These relations appear to hold for both transient and persistent systems. Furthermore, it is argued that the extremely strong coupling between hard X-rays and radio emission from black-hole X-ray binaries implies that the comptonising corona is simply the base of the jet. [ABSTRACT FROM AUTHOR]

We discuss constraints on the assembly history of supermassive black holes from the observed remnant black holes in nearby galaxies and from the emission caused by accretion onto these black holes. We also summarize the results of a specific model for the evolution of galaxies and their central black holes which traces their hierarchical build-up in CDM-like cosmogonies. The model assumes (i) that black holes, ellipticals and starbursts form during major mergers of galaxies (ii) that the gas fraction in galaxies decreases with decreasing redshift (iii) that the optically bright phase of a QSO lasts for about 107 years. The model successfully reproduces the evolution of cold gas as traced by damped Ly$\alpha$ systems, the evolution of optically bright QSOs, the remnant black hole mass distribution and the host-galaxy luminosities of QSOs. [ABSTRACT FROM AUTHOR]

Coalescing compact binaries with neutron star (NS) or black hole (BH) components are important sources of gravitational waves for the laser-interferometer detectors currently under construction, and may also be sources of gamma-ray bursts at cosmological distances. This paper focuses on the final hydrodynamic coalescence and merger of NS-NS binaries, and addresses the question of whether black-hole formation is the inevitable final fate of these systems. [ABSTRACT FROM AUTHOR]

The existence of supermassive collapsed objects in the cores of most galaxies poses still-unanswered questions. First, how did they form, and how does their mass depend on the properties of the host galaxy? Second, can observations probe the metric in the strong-field domain, testing whether it indeed agrees with the Kerr geometry predicted by general relativity (and, if so, what the spin is)? [ABSTRACT FROM AUTHOR]

Recent work on the dyadosphere of a black hole is reviewed with special emphasis on the explanation of gamma-ray bursts. A change of paradigm in the observations of black holes is presented. [ABSTRACT FROM AUTHOR]

The relatively nearby (40 Mpc) peculiar Type Ic supernova 1998bw was found in the error box of the Gamma Ray Burst GRB980425, and its explosion time coincided within less than one day with the time of the burst. The probability that this was a chance coincidence is less than 10-6, which strongly suggests that the GRB and the supernova are related. The spectrum and lightcurve of this supernova indicate that the exploding star was a carbon-oxygen star of about 10 M$_\odot$, and that the collapsing core had a mass of at least 3 M$_\odot$ (Iwamoto et al. 1998), too large for forming a stable neutron star. This indicates that here most probably a black hole was formed. The large radio emission of the supernova, with a synchrotron spectrum, indicates that here mass ejection took place with mildly relativistic velocities (v > 0.9c), presumably in the form of a jet, which likely was responsible for the GRB. Although this was intrinsically a very weak GRB, all this seems to provide support for the "collapsar"- or "hypernova"-model which links GRBs with the core collapse of a very massive star to a black hole, as was suggested by Woosley (1993) and Paczynski (1998), respectively. The recent discovery that the optical afterglow lightcurves of two "normal" GRBs at cosmological distances also show evidence for underlying supernova lightcurves similar to that of SN1998bw, provides further strong support for such a link. It thus appears that here for the first time we have been witnessing a new type of supernovae, which are the birth events of black holes as the final products of massive star evolution. Further studies will have to reveal what fraction of all GRBs can be connected with such events. [ABSTRACT FROM AUTHOR]

Many of the black hole accretion disk gamma-ray burst (BHAD GRB) models require the formation of black holes in short-period binaries. Although many uncertainties in the evolution of close binaries make it difficult to study the charcteristics of these GRB models, one of the most nefarious is our lack of understanding of stellar winds, both in giant/supergiant stars and in Wolf-Rayet stars. Here, we review the effects of winds on both the rates and redshift distribution of GRBs. These winds affect GRB models and X-ray binaries alike, and we can use observations of X-ray binaries to constrain mass-loss rates from winds. [ABSTRACT FROM AUTHOR]

We report the discovery of a strong overabundance of several $\alpha$-elements in the atmosphere of the star orbiting around the massive black hole in the binary system GRO J1655-40 (Nova Scorpii 1994). A high-resolution spectrum of this star obtained with the Keck I 10m telescope reveals the presence of extra strong absorption lines of O, Mg, Si, and S. Our analysis using spectral synthesis techniques and a suitable model atmosphere indicates that these elements are 6 to 10 times more abundant in the star than in the Sun. The overall spectrum of the companion resembles that of a normal subgiant star with a solar iron abundance. We interpret the enhanced abundances of $\alpha$-elements as a direct result of the nucleosynthesis in a supernova/hypernova explosion event associated with the progenitor of the black hole. This is to our knowledge up to now the most direct evidence for a link between a supernova explosion and the formation of a black hole. [ABSTRACT FROM AUTHOR]

The characteristics of black-hole X-ray binaries can be used to obtain information about their evolutionary history and the process of black-hole formation. In this paper I focus on systems with donor masses lower than the inferred black-hole masses. Current models for the evolution of hydrogen-rich, massive stars and of helium stars losing mass in a wind cannot explain the current sample of black-hole mass measurements. Assuming that the radial evolution of mass-losing massive stars is at least qualitatively accurate, I show that the properties of the BH companions lead to constraints on the masses of black-hole progenitors (at most twice the black-hole mass) and on the strength of winds in helium stars (fractional amount of mass lost smaller than about 50%). Constraints on common-envelope evolution are also derived. [ABSTRACT FROM AUTHOR]

Observations of massive binaries provide important constraints on the evolutionary fate of massive stars. Although stellar evolution in a binary system is different from single-star evolution, practically the only way to derive information on the progenitor masses of neutron stars and black holes is by studying massive binaries and their descendants. Wolf-Rayet binaries show a rather continuous mass distribution, while there might be a gap between the neutron-star and black-hole masses. Wray 977 (GX301-2) hosts the most massive OB star with X-ray pulsar companion, and sets an empirical lower mass limit for black-hole formation in a massive binary. HD153919 is the OB supergiant with earliest spectral type, and potentially the most massive OB star in a high-mass X-ray binary, but the nature of the X-ray source (4U1700-37) is not clear. Although it might be a low-mass black hole, new observations suggest it is a neutron star. [ABSTRACT FROM AUTHOR]

The progenitor evolution of the massive X-ray binary Wray 977 is investigated using new models of massive close binary evolution. These models yield constraints on the mass limit for neutron-star/black-hole formation in single stars, MBH. We argue for quasi-conservative evolution in this system, and we find MBH > 13...21 M$_\odot$ from the existence of a neutron star in Wray 977, the uncertainty being due to uncertainties in the treatment of convection. Our results revise earlier published much larger values of MBH derived from Wray 977. Then, on the basis of a grid of 37 evolutionary models for massive close binaries with various initial masses, mass ratios and periods, we show that in binaries the critical initial mass limit for neutron star/black hole formation is very different from the corresponding value in single stars. This implies that neutron-star and black-hole mass functions obtained for single stars cannot per se be compared to the masses of compact objects in binary systems. [ABSTRACT FROM AUTHOR]

A brief overview is given of the circumstances which allow a black hole to be formed in a binary. The importance of mass loss before the supernova explosion from the progenitor of the black hole is explained, as are the various ways in which this may happen and the properties of the resulting X-ray binaries. X-ray binaries in globular clusters are also discussed. We indicate recent interesting developments in theory, i.e. studies of mass transfer from a main-sequence donor, of the evolution of stellar cores without envelopes, of low-mass binaries with $\ge 2M_\odot$ donors; as well as in observations, e.g. the discovery by BeppoSAX of many soft X-ray transients with neutron stars. [ABSTRACT FROM AUTHOR]

We have developed a new Monte Carlo code to follow the long-term evolution of a spherical dense galactic nucleus with a central massive black hole (BH). The main physical processes taken into account are 2-body relaxation, collisions, tidal disruptions and BH's growth. Self-gravity, velocity anisotropy and a stellar mass spectrum are properly modeled. This tool enables us to get reliable predictions for the rate and characteristics of star destroying events that induce bright accretion phases. Here, we summarize the design concepts of this code and show the results of test calculations and preliminary investigations. [ABSTRACT FROM AUTHOR]

The study of supermassive black holes in the centers of galaxies has recently progressed from mere detection to using their correlations with galaxy properties to infer formational and evolutionary histories of both the galaxy and the black hole itself. In this paper, I present two recent conclusions concerning the black-hole surveys and galaxy models: 1) the ratio of black-hole mass to the brightness of the bulge component is now a factor of 5-10 smaller than previous estimates. This decrease is due mainly to the inclusion in our sample of galaxies not formerly thought to contain black holes; 2) The stellar orbital structure of the stars near the galaxy center show strang tangential velocity anisotropy. Theoretical models which best match this trend are black-hole binary /merger models. [ABSTRACT FROM AUTHOR]

Mergers of black-hole binaries are expected to release large amounts of energy in the form of gravitational radiation. However, binary evolution models predict merger rates too low to be of observational interest. In this paper we explore the possibility that black holes become members of close binaries via dynamical interactions with other stars in dense stellar systems. In star clusters, black holes become the most massive objects within a few tens of millions of years; dynamical relaxation then causes them to sink to the cluster core, where they form binaries. These black-hole binaries become more tightly bound by superelastic encounters with other cluster members, and are ultimately ejected from the cluster. The majority of escaping black-hole binaries have orbital periods short enough and eccentricities high enough that the emission of gravitational waves causes them to coalesce within a few billion years. We predict a black-hole merger rate of 10-8 to 10-7 per year per cubic megaparsec, implying gravitational-wave detection rates substantially greater than the corresponding rates from neutron star mergers. For the first generation Laser Interferometer Gravitational-Wave Observatory (LIGO-I), we expect about one detection during the first two years of operation. For its successor LIGO-II, the rate rises to roughly one detection per day. There is about an order of magnitude uncertainty in these numbers. [ABSTRACT FROM AUTHOR]

We review the literature of the past two decades on the possible evolution from the massive star Wolf-Rayet phase to the black hole phase, and on the masses of WR stars observed in binary systems. Of the 52 WR binaries in the VIIth Catalogue of Galactic Wolf-Rayet stars, the 19 WR binaries with measured radial-velocity (RV) orbits have masses MWN = 2-55 M$_\odot$ and MWC = 9-16 M$_\odot$. We discuss four candidate WR+BH systems: Cyg X-3, HD 197406, R 140a2, and Mk 34. [ABSTRACT FROM AUTHOR]

Globular clusters could harbor massive central black holes (BHs), just as galaxies do. So far, no unambiguous detection of a massive BH has been reported for any globular cluster. However, the dense core-collapsed cluster M15 seems to be a good candidate. I review the available photometric and kinematic data for this cluster. Both are consistent with a BH of mass $M_\bullet \approx 2000 M_\odot$, although such a BH is not unambiguously required by the data. I discuss some ongoing studies with Keck and HST which should shed more light on this issue in the coming years. [ABSTRACT FROM AUTHOR]

We have surveyed two large samples of nearby low-luminosity AGN with the VLA to search for flat-spectrum radio cores, similar to Sgr A* in the Galactic Center. Roughly one third of all galaxies are detected (roughly one half if HII transition objects are excluded from the sample), many of which have compact radio cores. Follow-up observations with the VLBA have confirmed that these cores are non-thermal in origin, with brightness temperatures of $\ge 10^8$ K. The brightest of these are resolved into linear structures. The radio spectral indices of the cores are quite flat ($\alpha \sim 0$), with no evidence for the highly inverted radio cores predicted in the ADAF model. Spectrum and morphology of the compact radio emission is typical for radio jets seen also in more luminous AGN. The emissionline luminosity seems to be correlated with the radio core flux. Together with the VLBI observations this suggests that optical and radio emission in at least half the low-luminosity Seyferts and LINERs are black-hole powered. We find only a weak correlation between bulge luminosity and radio flux and an apparently different efficiency between elliptical and spiral galaxies for producing radio emission at a given optical luminosity. [ABSTRACT FROM AUTHOR]

The phenomenology of jets associated with a variety of black hole systems is summarized, emphasizing the constraints imposed on their origin. Models of jet formation are reviewed, focusing in particular on recent ideas concerning MHD models. Finally, the potential for advancing our understanding of jets both through future observations - especially forthcoming X-ray missions - and for elucidating some crucial theoretical questions is highlighted. [ABSTRACT FROM AUTHOR]

Relativistic outflows are a common phenomenon in accreting black holes. Despite the enormous differences in scale, stellar-mass black holes in binaries and supermassive black holes in galactic nuclei produce jets with analogous properties. In both two types of relativistic outflows are observed: 1) steady compact jets with flat-spectrum, and 2) sporadic extended jets with steep-spectrum and apparent superluminal motions. Besides, the most common class of gamma-ray bursts are afterglows from ultra-relativistic jets associated to the formation of black holes at cosmological distances. [ABSTRACT FROM AUTHOR]

In this paper we describe the upcoming European gamma-ray observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory). This ESA satellite is scheduled to be launched in the Autumn of 2001 on board of a Russian Proton rocket. INTEGRAL hosts two main gamma-ray instruments: an imager (IBIS) and a spectrometer (SPI). These two gamma ray instruments are complemented with two monitoring instruments: an X-ray monitor (JEM-X) and an optical monitor (OMC). All four instruments will be observing simultaneously the same part of the sky. The instruments will allow detailed imaging (angular resolution up to 12') and spectroscopic (energy resolution up to 2 keV at 1.3 MeV) observations in an energy band between 20 keV and 10 MeV. Possible targets for INTEGRAL include the galactic center, black hole binaries, and AGNs. [ABSTRACT FROM AUTHOR]

There is now ample evidence that most - perhaps all - galactic spheroids host a supermassive BH at their center. This has been assessed using a variety of observational techniques, from stellar and/or gas dynamics to megamasers. Yet another promising technique is offered by the case of the Virgo elliptical NGC 4552, in which early HST/FOC observations revealed a central low-luminosity flare. Subsequent HST/FOS observations with a 0.21 arcsec aperture have revealed a rich emission-line spectrum with broad and narrow components with FWHM of 3000 and 700 km/s, respectively. This variable, mini-AGN at the center of NGC 4552 is most naturally the result of a sporadic accretion event on a central BH. It has a H$\alpha$ luminosity of only $\sim 10,000 L_\odot$, making it the likely, intrinsically faintest AGN known today. Only thanks to the superior resolution of HST such a faint object has been discovered and studied in detail, but adaptive optics systems on large ground-based telescopes may reveal in the future that a low level of accretion onto central massive BHs is an ubiquitous phenomenon among galactic spheroids. FOC/FOS observations of a central spike in NGC 2681 reveal several analogies with the case of NGC 4552, while yet another example is offered by a recent exciting finding with STIS by R.W. O'Connell in NGC 1399, the third galaxy in our original program. [ABSTRACT FROM AUTHOR]

I show that the Eddington limit implies Pcrit(BH) $\simeq 3.3$ d, i.e. a critical orbital period beyond which black-hole LMXBs cannot appear as persistent systems. The unusual behaviour of GRO J1655-40 may result from its location close to Pcrit(BH). [ABSTRACT FROM AUTHOR]

Black hole X-ray binaries are transient probably because their discs are subject to the same thermal-viscous instability which is present in dwarf nova binary systems. I discuss applications of the dwarf-nova instability model to transient, low-mass, X-ray binary systems. When disc truncation and X-ray irradiation are taken into account this model is capable of reproducing the basic properties of X-ray binary outbursts [3]. [ABSTRACT FROM AUTHOR]

This paper gives an overview of the observed X-ray spectra of lowmass X-ray binaries containing a weakly-magnetized neutron star (NS-LMXRB) and those of X-ray binaries containing a black hole (BH-XRB). The X-ray spectra of these systems change with luminosity (the mass-accretion rate). At high X-ray luminosities ( Lx > 1037 erg s-1), while soft thermal emission from the accretion disk dominates, there is a distinct difference in the X-ray spectrum between NS-LMXRBs and BH-XRBs. At a lower luminosity (typically $L_x \sim 10^{37}$ erg s-1), both systems undergo transitions between a soft thermal state and a hard powerlaw state. The characteristics of these X-ray spectra are discussed. [ABSTRACT FROM AUTHOR]

In the recent years, thanks to the RXTE satellite, our knowledge of the properties of aperiodic time variability of compact binaries increased enormously. Here I briefly summarize the current status both for neutron star and black hole systems and concentrate on the similarities between these two classes. I show that there is increasing evidence that the main processes that produce the variability are the same for black holes and neutron stars. [ABSTRACT FROM AUTHOR]

Accreting black holes and neutron stars at luminosities above 0.01 of the critical Eddington luminosity have a lot of similarities, but also drastic differences in their radiation and power density spectra. The efficiency of energy release due to accretion onto a rotating neutron star usually is higher than in the case of a black hole. The theory of the spreading layer on the surface of an accreting neutron star is discussed. It predicts the appearance of two bright belts equidistant from the equator. This layer is unstable and its radiation flux must vary with high frequencies. [ABSTRACT FROM AUTHOR]

The SINFONI integral field spectrometer for the VLT will provide nearinfrared spatially resolved spectra at spatial resolutions close to the diffraction limit of the telescope ( $0^{\prime\prime}\hspace{-0.15cm}.05$ at $2\mu$m). 1024 spectra can be simultaneously obtained, covering a 32 x 32 pixel field of view with $\sim 100$% filling factor. The spectral resolution is R $\sim 4500$, corresponding to a kinematic resolution of 67 km s-1 .SINFONI is ideally suited to study stellar kinematics in the nuclear regions of normal spiral galaxies, using the near-infrared H and K band CO stellar absorption features. Integral field data from SINFONI will provide high-resolution two-dimensional maps of nuclear velocity dispersion and rotation, which in turn will constrain the anisotropy parameter and yield robust estimates of the central dark mass. [ABSTRACT FROM AUTHOR]

The high mass X-ray binary, Cyg X-1, was for many years the strongest candidate for a stellar-mass black-hole in the Galaxy. It very likely is a black-hole, but it is the "soft X-ray transients", a sub-class of low-mass X-ray binaries, that have revolutionised our ability to accurately measure compact object masses. This is accomplished via optical and IR photometry and spectroscopy of the mass-losing star during the extended X-ray quiescent periods, exploiting essentially classical binary astronomy techniques. I will summarise the optical and IR properties of these objects and review some of the more recent results. [ABSTRACT FROM AUTHOR]

Gaseous and/or stellar kinematics obtained via long-slit spectrography are routinely used to reveal the presence of supermassive black holes (SBHs) in galactic nuclei. Both have their advantages and drawbacks, including the difficulty of building realistic stellar kinematical models or to deal with the contribution of non-gravitational forces in the gas kinematics. In this paper, I present 2D spectrographic and some HST/WFPC2 observations of the gas and stellar components in a small sample of early-type galaxies, demonstrating the need for both high resolution and bidimensional spatial coverage to understand the structure and dynamics of their central regions, and in particular to test the presence of SBHs. [ABSTRACT FROM AUTHOR]

The Space Telescope Imaging Spectrograph (STIS) has obtained high resolution (with $\Delta V \gtrsim 20$ km s-1 and $FWHM \sim 0.1-0.2$") spectra of the nuclei of about 15 nearby galaxies in a search for supermassive black holes. This talk concentrates on the data reduction process and the difficulties which have to be overcome to obtain reliable kinematic measurements from STIS observations. Our analysis is based on standard STIS-pipeline software (GSFC's IDL version of the CALSTIS package). We have added significant functionality to address the undersampling of the spatial part of the point-spread function and the presence of cosmic rays in the images. Typically $\sim 20$% of the total counts are cosmic-ray hits, in 5% of the pixels. We also present preliminary results of the nuclear kinematics for several galaxies for which Rutgers astronomers are lead investigators. In NGC 2841 we obtain a clear signature in the kinematics of a black hole with mass of several tens of million solar masses, the first black hole detection in this galaxy. In M 87 we measure the stellar velocity dispersion at a radius of 0.3", similar to ground-based data, but with far less contamination from adjacent parts of the image. [ABSTRACT FROM AUTHOR]

Masses of black holes in nearby galactic nuclei can be measured in a variety of ways, using stellar and gaseous kinematics. Reliable black-hole masses are known for several dozen objects, so that demographic questions can start to be addressed with some confidence. Prospects for the near future are discussed briefly. [ABSTRACT FROM AUTHOR]

Four years ago, we initiated a proper motion study of the Galaxy's central stellar cluster using diffraction-limited K[$2.2\mu m$]-band images obtained with the W.M. Keck I 10-m telescope. With relative positional accuracies of $\sim 3$ milliarcsec, we have been able to measure stars moving with velocities up to 1400 km s-1 and, for the first time ever, accelerations of 1-3 mas yr-2 (0.1-0.3 cm s-2) at projected distances from the apparent radio counterpart of the black hole, Sgr A*, of 0.004 pc (0.1 arcsec). These measurements have not only provided us with direct dynamical evidence for a 2.6 x 106 M$_\odot$ central black hole, but have also permitted us to begin to constrain the orbits of these stars, which appear to be bound to the central mass. Continued study of these orbits (which possibly have periods as short as 10 years) will allow us to infer the radial distribution of dark matter within a few hundredths of a parsec around the black hole. [ABSTRACT FROM AUTHOR]

Recent spectroscopic and imaging data provide new evidence for the presence of a massive black hole at the center of the Milky Way. The most recent results are based on new near-infrared observations of the central stellar cluster of our Galaxy conducted with the infrared spectrometer ISAAC at the ESO VLT UT1 and the MPE speckle camera SHARP at the ESO NTT. These data demonstrate clearly that there is no strong CO band head absorption originating in the northern part (S1/S2 area) of the central stellar cluster at the position of Sgr A* . This makes it likely that these K$\sim14.5$ stars are O9 - B0.5 stars with masses of 15 to 20 M$_\odot$. We also report the detection of Br$\gamma$ line emission at the position of the central stellar cluster which could be associated with the ‘mini-spiral' rather than with the Sgr A* cluster itself. The combined data on radial velocities and proper motions show that the overall stellar motions are very close to isotropy. They indicate a central mass concentration with a density $\ge 10^{12.6}$ M$_\odot$ pc-3 that dominates the potential between 0.01 and 1 pc. The derived mass ranges between 2.6 and 3.3 x 106 M$_\odot$ for a distance of 8.0 kpc. Such a mass concentration cannot be stable and must be present in the form of a black hole. [ABSTRACT FROM AUTHOR]

New observational techniques and theoretical ideas are enabling us to find black holes and measure their masses with increasing precision, and we may soon be able to measure black hole spins. We are now in a position to study the formation and demography of black holes, and to develop a deeper understanding of how they interact with their environments. [ABSTRACT FROM AUTHOR]

The advent of the large effective apertures of the Keck telescopes has resulted in the determination with unprecedented accuracy of the mass functions and mass ratios of faint ($R \approx 21$ mag) X-ray transients (GS 2000+25, GRO J0422+32, Nova Oph 1977, Nova Vel 1993). [ABSTRACT FROM AUTHOR]

The maximum mass of neutron stars is one of the most important predictions of the general relativistic theory of stellar structure. This paper highlights the difficulties in making a definitive prediction, and also reviews the progress made so far. [ABSTRACT FROM AUTHOR]

I review attempts made to determine the properties of neutron stars. The focus is on the maximum mass that a neutron star can have, or, conversely, the minimum mass required for the formation of a black hole. There appears to be only one neutron star for which there is strang evidence that its mass is above the canonical $1.4 M_\odot$, viz., Vela X-1, for which a mass close to $1.9 M_\odot$ is found. Prospects for progress appear brightest for studies of systems in which the neutron star should have accreted substantial amounts of matter. [ABSTRACT FROM AUTHOR]

I am truly happy to be back here at ESO for a short visit and see so many colleagues and friends with whom we have shared the last few years of wonderful enterprises. I am truly touched by the honor you have wanted to do me by organizing this symposium. The only fly in the ointment for me has been that Lex Kaper had convinced me to give a talk before I realized what was happening. Between the recent physical move to the U.S. with my papers in transit, my continual conceptual move to the red from X-rays to visible to millimeter astronomy and the excitement of the Chandra launch, I was lucky to find somee viewgraphs to share with you. I was sustained in the thought (I believe due to Pascal) that one should not underestimate the pleasure that people have in listening to something they already know. [ABSTRACT FROM AUTHOR]

We report new results on the stellar kinematics and the mass distribution of the galaxy NGC 3115 based on NIR integral field spectroscopic data. Investigations using long slit spectroscopic data have yielded strong evidence for the presence of a massive dark object of ca. 109 solar masses. NGC 3115 therefore appears to be a prominent candidate for hosting a black hole in its center. We demonstrate that with integral field spectroscopy the rotation and velocity dispersion can be much better constrained by sampling in both spatial dimensions. This yields revised and more secure results. [ABSTRACT FROM AUTHOR]

The theory of coronal evaporation predicts the formation of an inner hole in the cool thin accretion disk for mass accretion rates below a certain threshold and the sudden disappearance of this hole when the mass accretion rate rises above that threshold. This appears to quantitatively account for the observed transitions between hard and soft spectral states at critical luminosities. [ABSTRACT FROM AUTHOR]

The formation of supermassive black holes is not fully understood. The proposed mechanisms predict the formation of these at late times. We study a new scenario where black holes form in a CDM cosmology. While the baryons are smoothly distributed until after the recombination era, cold dark matter decouples early from background expansion, allowing the dark matter inhomogeneities to grow long before recombination. After recombination baryonic matter decouples from photons and falls into the deep gravitational potential wells of the dark component. [ABSTRACT FROM AUTHOR]

When the iron core of a (non-rotating) massive star collapses to a neutron star there are three possible outcomes. First, if a neutrino powered explosion of sufficient intensity develops, almost all the material outside the neutron star is ejected and a typical supernova of about 1051erg produced. If the neutrino powered explosion does not develop, then a black hole forms in the time it takes for the proto-neutron star to accrete a few tenths of a solar mass - a second or so. But there is a third intermediate possibility that we explored in some detail here. A shock is be launched initially, but lacks adequate energy to eject all the overlying matter. Then, after a time that is highly sensitive to the initial shock energy, mass falls back to the origin, accretes, and possibly produce a black hole. In SN 1987A, an explosion of roughly $1.2\cdot10^{51}$erg in a 20 M$_\odot$ blue supergiant, it was previously estimated that roughly 0.1 M$_\odot$ re-imploded in this way (Chevalier 1989). [ABSTRACT FROM AUTHOR]

The measured radial velocities, and the recently derived tangential velocities based on Hipparcos observations, have demonstrated that several high-mass X-ray binaries (HMXBs) with OB-supergiant companion travel through interstellar space with velocities on the order of 50 km s-1. On theoretical grounds it is expected that all HMXBs are runaway systems, since the loss of mass from the system during the supernova explosion of the compact star's progenitor results in a kick to the remaining (bound) binary system. When a massive star is running through space with a supersonic velocity, the interaction of its stellar wind with the interstellar medium will result in the formation of a bow shock. The detection of a wind bow shock around a high-mass X-ray binary would be an indication that the system is moving with a high space velocity, and from its shape the direction of motion could be derived. Especially for systems at larger distances, for which no Hipparcos measurements are available, the detection of a bow shock would be a valuable diagnostic. We searched for the presence of bow shocks around high-mass X-ray binaries using infrared observations. Up to now, we have only one firm detection out of 12 candidates, while for (apparently single) OB runaway stars the detection rate is about 30% [5]. A new hypothesis to explain this difference is put forward. [ABSTRACT FROM AUTHOR]

We present a detailed evolutionary sequence for Cygnus X-2, and calculate possible dynamical orbits of the system in a realistic Galactic potential. [ABSTRACT FROM AUTHOR]

Both the recently observed high runaway velocities of Cyg X-1 ($\sim 50$ km s-1) and X-ray Nova Sco 1994 ($\ge 100$ km s-1) and the relatively low radial velocities of the black hole X-ray binaries with low mass donor stars, can be explained by symmetric mass ejection in the supernovae (SNe) which formed the black holes in these systems. We find that at least $2.6M_\odot$ and $4.1M_\odot$ must have been ejected in the formation of Cyg X-1 and Nova Sco, respectively. A possible kick at the formation of the black hole is not needed to explain their space velocities. [ABSTRACT FROM AUTHOR]

We are carrying out a programme of non-linear, time-dependent calculations to study non-stationary accretion onto black holes. We plan to use this study as a basis for considering whole populations of accreting objects. Some of the most interesting results are presented. [ABSTRACT FROM AUTHOR]