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A decade after their first discovery, the origin of giant supermassive black holes (SMBHs), with masses in excess of 109 M⊙, at redshifts as early as z > 6, remains a puzzle. One possibility is that stellar-mass “seed” BHs, left behind by the first stars, accrete gas at close to the Eddington limit during a large fraction (≳ 50%) of the time. While maintaining such a high accretion rate may itself be difficult, here we focus on another, less commonly discussed problem in this scenario: unless BH seed formation and growth are preferentially suppressed in less massive protogalaxies, the mass density in M∼106M⊙ SMBHs at z ∼ 6 already exceeds the locally observed SMBH mass density by several orders of magnitude. We show that the X-rays from the earliest accreting BHs themselves can cause a self-regulation, by partially ionizing and heating the intergalactic medium (IGM). This “global warming” suppresses the formation and growth of subsequent generations of BHs in low-mass halos, and can produce excellent agre...

We demonstrate the feasibility of discovering supermassive black hole (SMBHs) in “normal” spiral galaxies using a combination of X‐ray selection and multi‐wavelength follow‐up. We carried out a Chandra survey of nearly face‐on spiral galaxies and uncovered a population of low‐mass SMBHs providing a way to investigate the low‐mass end of the local BH mass function. We were sensitive to Eddington luminosity ratios as low as 10−6. Some galaxies with small or no bulges also appear to host SMBHs. This calls into question whether the fundamental property related to a nuclear SMBH is the bulge or the dark matter halo.

The final mass of the first star is fixed when mass accretion to a protostar ceases. We report our recent 2‐dimensional radiation‐hydrodynamic simulations of the mass accretion process to the primordial protostar. The protostellar evolution is also simultaneously calculated by solving the stellar interior structure. Our preliminary calculation shows that a circumstellar disk forms around the primordial protostar. The disk is almost fully molecular, and surrounded by warmer neutral envelope. Mass accretion to the star takes place via this accretion disk at high rates exceeding several×10−3 M⊙ yr−1. With such high accretion rates, total luminosity of the protostar approaches the Eddington luminosity before the protostar reaches the zero‐age main sequence stage. Radiation pressure exerted on gas accretion envelope should regulate the mass accretion when the protostellar mass exceeds 80 M⊙, which is before the stellar UV radiation influences the accretion flow.

X‐ray bursters form a class of Low Mass X‐Ray Binaries where accreted material from a donor star undergoes rapid thermonuclear burning in the surface layers of a neutron star. The flux released can temporarily exceed the Eddington limit and drive the photosphere to large radii. Such photospheric radius expansion bursts likely eject nuclear burning ashes into the interstellar medium, and may make possible the detection of photoionization edges. Indeed, theoretical models predict that absorption edges from 58Fe at 9.2 keV, 60Zn and 62Zn at 12.2 keV should be detectable by the future missions Simbol‐X and NuSTAR. A positive detection would thus probe the nuclear burning as well as the gravitational redshift from the neutron star. Moreover, likely observations of atomic X‐ray spectral components reflected from the inner accretion disk have been reported. The high spectral resolution capabilities of the focusing X‐ray telescopes may therefore make possible to differentiate between the potential interpretations...

We analyze the clustering properties of quasars simulated using a semianalytic model built on the Millennium Simulation, with the goal of testing scenarios in which black hole accretion and quasar activity are triggered by galaxy mergers. When we select quasars with luminosities in the range accessible by current observations, we find that predicted values for the redshift evolution of the quasar bias agree rather well with the available data and the clustering strength depends only weakly on luminosity. This is independent of the lightcurve model assumed, since bright quasars are black holes accreting close to the Eddington limit. We also used the large catalogues of haloes available for the Millennium Simulation to test whether recently merged haloes exhibit a stronger large-scale clustering than the typical haloes of the same mass. This effect might help to explain the very high clustering strength observed for z~4 quasars. However, we do not detect any significant excess bias for the clustering of merger remnants, suggesting that objects of merger-driven nature do not cluster significantly differently than other objects of the same characteristic mass., 4 pages, 2 figures. To appear in the proceedings of "The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", Eds. Sebastian Heinz, Eric Wilcots (AIP conference series)

The most massive stars born on the main sequence display pulsations that are excited by several processes: the epsilon process; a poorly investigated process that excites the extensive mass loss of Wolf Rayet stars; and the Eddington luminosity coupled with convection in the luminous blue variable stars. Here we discuss details involved in the luminous blue variables, and how their growing pulsations can produce outbursts that reduce the total mass of the star to a level where the pulsations no longer grow. This process limits the most massive stars possible in our galaxy to 100 solar masses or less.

Radiative force plays an important role in setting structure of stellar atmospheres. If radiative force overcomes gravity, stellar wind appears. In O and B stars, force coming from radiation absorbed by spectral lines of metals dominates the radiative force. However, in first stars metals are not present, the radiative force is dominated by contribution of continuum hydrogen and helium absorption, and does not overcome gravity. Since no stellar wind is present in these stars, static model atmospheres are suitable. However, if such star is close to the Eddington limit, calculation procedure is often unstable.

Recent observations on both microquasars and AGNs with radio and X‐ray telescopes have revealed remarkable radio/X‐ray correlation of these objects. Because the radio and X‐ray emissions are mainly emitted from jet and accretion flow, the radio/X‐ray correlation can be used to probe the accretion‐jet physics in these accreting black hole systems. Using a uniform broad line SDSS AGN sample, we derived the black hole fundamental plane relationship among the 1.4 GHz radio luminosity (Lr), 0.1–2.4 keV X‐ray luminosity (LX), and black hole mass (M). We found from our sample that the fundamental plane relation has a very weak dependence on the black hole mass, and a tight correlation also exists between the Eddington luminosity scaled X‐ray and radio luminosities for the radio quiet subsample. In addition, we noticed that radio‐loud AGNs have steeper power‐law slope in the radio/X‐ray correlation than radio‐quiet AGNs. This is mainly due to the different origin of X‐ray emissions in radio‐loud and radio‐quiet A...

Recent analysis of the RXTE X‐ray spectra of Sco X‐1 discovered that Sco X‐1 can be adequately modeled by a simple two‐component model of Compton up‐scattering with a soft photon electron temperature of about 0.4 keV, plus an Iron K‐line. The results show a strong correlation between spectral power law index and kHz QPOs. Sco X‐1 is the prototypical Z‐source low‐mass X‐ray binary (LMXB) system radiating near the Eddington limit. This radiation produces a high radiation pressure in its Compton cloud. We infer that the radiation pressure produces a geometrical configuration of the cloud that is quasi‐spherical. We conclude that the high Thomson optical depth of the Compton cloud, in the range of 5–6 from the best‐fit model parameters, is consistent with the neutron star's surface being obscured by material, which would likely suppress a spin frequency of Sco X‐1 due to photon scattering off cloud electrons. We also demonstrate the evolution of its power spectrum when Sco X‐1 transitions from the horizontal branch to the normal branch.

Continuum driving is an effective method to drive a strong stellar wind. It is governed by two limits: the Eddington limit and the photon-tiring limit. A star must exceed the effective Eddington limit for continuum driving to overcome the stellar gravity. The photon-tiring limit places an upper limit on the mass loss rate that can be driven to infinity, given the energy available in the radiation field of the star. Since continuum driving does not require the presence of metals in the stellar atmosphere it is particularly suited to removing mass from low- and zero-metallicity stars and can play a crucial part in their evolution. Using a porosity length formalism we compute numerical simulations of super-Eddington, continuum driven winds to explore their behaviour for stars both below and above the photon-tiring limit. We find that below the photon tiring limit, continuum driving can produce a large, steady mass loss rate at velocities on the order of the escape velocity. If the star exceeds the photon-tiring limit, a steady solution is no longer possible. While the effective mass loss rate is still very large, the wind velocity is much smaller, Comment: to be published in the conference proceedings of: First Stars III, Santa Fe, 2007

Accretion at rates exceeding the Eddington limit is common in close binaries and in AGN. Hyperaccreting binaries appear as ultraluminous X‐ray sources when viewed close the the inner accretion disc axis, and like SS433 when viewed from other angles. I show that AGN are unlikely to achieve electron‐scattering Eddington ratios as high as ULXs, but hyperaccretion of dusty matter is common among AGN. The resulting outflow may well be the origin of the dusty torus invoked in unified AGN schemes.

The question whether quiescent black hole X-ray binaries are capable of powering relativistic outflows is addressed by means of simultaneous radio/X-ray observations of a nearby system steadily emitting X-rays below 1e-8 times the Eddington luminosity. The robust detection of a radio counterpart suggests that a synchrotron emitting outflow is being powered by this system, even though its degree of collimation remains unknown, and hard to investigate. With the inclusion of the A0620-00 data, the non linear radio/X-ray correlation for hard state black hole X-ray binaries appears to hold down to very low quiescent luminosities. However, an increasing number of outliers is being found at higher luminosities, questioning the universality of such correlation, or at least its normalization., Invited talk at `The Multicoloured Landscape of Compact Objects and their Explosive Origins', Cefalu', 2006 June 11-24 (AIP Conf. Proc.)

Computing the basic accretion parameters for the supermassive black holes expected to be present in quasars is still a major challenge. In this paper we stress how a systematization of observational properties through the so‐called “eigenvector 1” of quasars helps to develop a clearer view of the structure and dynamics of the Broad Line Region. “Eigenvector 1”‐based results also provide guidelines for more reliable estimates of the black hole mass and Eddington ratio over a wide redshift range, 0 ≲ z ≲ 2.5. We summarize the results of computations for a sample of ≈ 300 low and intermediate redshift quasars, and we suggest that black hole masses may not generally exceed ≈ 5 ⋅ 109 M⊙. We also found no convincing evidence of sources radiating above the Eddington limit.

We present a new technique for identifying stellar mass black holes in low mass X-ray binaries (LMXBs), and apply it to XMM-Newton observations of M31. We examine X-ray time series variability seeking power density spectra (PDS) typical of LMXBs accreting at a low accretion rate (which we refer to as Type A PDS); these are very similar for black hole and neutron star LMXBs. Galactic neutron star LMXBs exhibit Type A PDS at low luminosities (~10^36--10^37 erg/s) while black hole LMXBs can exhibit them at luminosities >10^38 erg/s. We propose that Type A PDS are confined to luminosities below a critical fraction of the Eddington limit, $l_c$ that is constant for all LMXBs; we have examined asample of black hole and neutron star LMXBs and find they are all consistent with $l_c$ = 0.10+/-0.04 in the 0.3--10 keV band. We present luminosity and PDS data from 167 observations of X-ray binaries in M31 that provide strong support for our hypothesis. Since the theoretical maximum mass for a neutron star is \~3.1 M_Sun, we therefore assert that any LMXB that exhibits a Type A PDS at a 0.3--10 keV luminosity greater than 4 x 10^37 erg/s is likely to contain a black hole primary. We have found eleven new black hole candidates in M31 using this method. We focus on XMM-Newton observations of RX J0042.4+4112, an X-ray source in M31 and find the mass of the primary to be 7+/-2 M_Sun, if our assumptions are correct. Furthermore, RX J0042.4+4112 is consistently bright in \~40 observations made over 23 years, and is likely to be a persistently bright LMXB; by contrast all known Galactic black hole LMXBs are transient. Hence our method may be used to find black holes in known, persistently bright Galactic LMXBs and also in LMXBs in other galaxies., 6 Pages, 6 figures. To appear in the conference proceedings of "Interacting Binaries: Accretion, Evolution and Outcomes" (Cefalu, July 4-10 2004)

A nova outburst is not only the third most violent explosion that can occur in a galaxy, it is the largest hydrogen bomb in the Universe. The last meeting devoted purely to studies of novae was held in Madrid in 1989. At that time IUE spectra of novae were just beginning to be analyzed in detail, the EXOSAT x‐ray results had just been published, and ROSAT had yet to be launched. Since that time, the IUE studies of novae in the LMC (known distance and small reddening) showed that all fast novae exceed the Eddington luminosity at maximum which was not predicted by numerical hydrodynamic simulations. A number of novae have now been observed in x‐rays with ROSAT, BEPPOSAX, ASCA, CHANDRA, and XMM (plus others). The x‐ray studies determined the turn off times for several classical novae, showed that at maximum x‐ray light they resemble the Super Soft Sources, and found rapid variations in the x‐ray light curves of two novae. There have been abundance analyses of V838 Her (oxygen poor, sulfur rich), LMC 1991, and other classical and recurrent novae. Infrared studies have resulted in a number of puzzling results such as the same nova producing both carbon (first) and silicate (later) dust at different times during its outburst. There have been advances in theoretical modeling and most studies now include large nuclear reaction networks combined with the hydrodynamic calculations. One perplexing problem produced by the simulations is that they predict that much less mass is ejected in the outburst than is observed, and the problem has worsened as the input physics has improved. Nevertheless we have made significant progress in the past 100 years and I will present some of the more important developments that have occurred over the past century. I will end with a list of questions to be answered.A nova outburst is not only the third most violent explosion that can occur in a galaxy, it is the largest hydrogen bomb in the Universe. The last meeting devoted purely to studies of novae was held in Madrid in 1989. At that time IUE spectra of novae were just beginning to be analyzed in detail, the EXOSAT x‐ray results had just been published, and ROSAT had yet to be launched. Since that time, the IUE studies of novae in the LMC (known distance and small reddening) showed that all fast novae exceed the Eddington luminosity at maximum which was not predicted by numerical hydrodynamic simulations. A number of novae have now been observed in x‐rays with ROSAT, BEPPOSAX, ASCA, CHANDRA, and XMM (plus others). The x‐ray studies determined the turn off times for several classical novae, showed that at maximum x‐ray light they resemble the Super Soft Sources, and found rapid variations in the x‐ray light curves of two novae. There have been abundance analyses of V838 Her (oxygen poor, sulfur rich), LMC 1991, an...

Some basic conditions, to be satisfied by any model of the ejected envelope, are given. Firstly it is recalled that reasons exist, for believing, that in early stages after optical maximum the expansion velocities in the envelope are generally larger at smaller radial distances. Indications, suggesting the opposite conclusion from the examination of emission lines, can be misleading. The highest velocities appear to be those of a wind. However Hubble flows are probably present in other stages for fast novae such as before optical maximum, while in addition the collisions between and overtaking of layers, can lead to a re‐establishment of such flows in late stages. On the theoretical side the Kato and Hachisu models are physically consistent, but cannot explain the flows when luminosities are above the Thomson scattering Eddington limit. Finally published models based on detailed non‐LTE radiative transfer calculations need to be modified, so as to become dynamically self consistent.

In 1999, Cheng, Fan, Zheng proposed a method to determin the parameters: the central black hole mass, M, the Doppler factor, δ, the propagation angle of the γ-rays with respect to the symmetric axis of a two-temperature accretion disk, Φ, and the distance (i.e. the height above the accretion disk), d at which the γ-rays are created. In that method, available variability timescales in gamma-ray bands, the absorption effect of a γ-ray and the beaming effect have been taken into account. In this paper, we adopte this method to a larger sample. Our results indicate that, if we take the intrinsic γ-ray luminosity to be λ times the Eddington luminosity, Lγin=λLEdd., the masses of the blazars are in the range of (1.5∼83)×107M◎ (λ=1.0) or (2.2∼131)×107M◎ (λ=0.1), the Doppler factors (δ) lie in the range of 0.17 to 3.72 (λ=1.0) or 0.25 to 5.33 (λ=0.1), the angle (Φ) is in the range of 10° to 68° (λ=1.0) or 10° to 63° (λ=0.1), and the distance (d) is in the range of 20.5Rg to 750Rg (λ=1.0) or 18Rg to 680Rg (λ=0.1).

Tidal disruption flares are differentiated into two classes -- those which are sub-Eddington and those which radiate near the Eddington limit. Flares from black holes above ~2 x 10^7 M_\odot will generally not radiate above the Eddington limit. For a Schwarzschild black hole, the maximum bolometric luminosity of a tidal disruption is ~L_Edd(5 x 10^7 M_\odot), substantially below the Eddington luminosities of the most massive disrupting black holes (~2 x 10^8 M_\odot). Bolometric corrections to the spectra of the brightest flares are found to be large (~7.5 mag). Nevertheless, the brightest flares are likely to have absolute magnitudes in excess of -19 in V and -21 in U (in the absence of reddening). Because the spectra are so blue, K-corrections may actually brighten the flares in optical bands. If such flares are as frequent as believed, they may soon be detected in low or high redshift supernovae searches. The He II ionizing radiation produced in the flares may dominate that which is produced by all other sources in the centers of quiescent galaxies, creating a steady state, highly ionized, fossil nebula with an extent of ~1 kpc which may be observable in recombination lines.

Many of the unidentified >100 MeV EGRET γ-ray sources are conjectured to originate from a population of isolated ≈10–100 M⊙ black holes accreting from the ISM. The low-latitude sources are mostly distant (∼several kpc) black holes accreting from high density molecular gas, whereas the medium latitude sources are black holes within a few hundred pc which accrete from the more tenuous local ISM. The γ-ray luminosity is assumed to be proportional to the Bondi-Hoyle accretion rate, and the nearby and distant sources have γ-ray powers of ≲1033 ergs s−1 and ≳1035 ergs s−1, respectively, in both cases far below the Eddington luminosity. The number of sources is compatible with estimates of black hole formation rates. In contrast to a pulsar origin for the unidentified sources, this model can account for γ-ray flux variability.

Aquila X-1 is one of the most active of the soft x-ray transients (SXTs). Soft x-ray outbursts can produce emission close to the Eddington limit in the 1–10 keV band and are typically observed about once a year. Between becoming operational in the spring of 1991, and the beginning of 1996, BATSE observed at least three episodes of hard x-ray emission lasting 50 days or longer, during which the 20–100 keV flux exceeded 50 mCrab [1]. XTE-ASM has observed two outbursts in the 2–10 keV range since becoming operational in early 1996. One of these outbursts was also observed by BATSE. The cause of the hard x-ray emission, and its relation to the soft x-ray emission, is still unknown.

Chi-squared analysis of the combined BATSE/PVO peak flux distribution places constraints on the luminosity function of gamma-ray bursts in a Λ=0, Ω0=1 Friedmann cosmology with a non-evolving density distribution. The analysis indicates that the minimum burst luminosity, the maximum burst luminosity, or both, are constrained, with the opposite end of the luminosity function often unconstrained. For this cosmological model, a non-zero width of the intrinsic luminosity function is preferred, but luminosity functions are forbidden that let many bursts from an extremely broad luminosity range be observed.

Constraints are found on the Galactic gamma‐ray burst luminosity function (assumed to be a truncated power law), assuming gamma‐ray bursts to be Galactic. Although most observed bursts span a narrow luminosity range, the intrinsic luminosity range can be very large. Angular isotropy additionally constrains the intrinsic luminosity range to be less than a factor of 5 for power‐law indices between −1 and 5, and requires either the maximum luminosity, the minimum luminosity, or both to be between 7.6×1041 and 1.5×1042 erg sec−1.

We study numerically the quasi‐spherical accretion of matter on to a compact object (neutron star or black hole). Anisotropic x‐ray luminosity, powered by mass accretion, heats the accreting gas through Compton scattering. When the gas temperature increases above the local escape temperature, part of the accreting gas will flow outwards as a result of the action of buoyancy force. The direction of the outflow coincides with the maximum of the x‐ray luminosity. The depth of outflow is correlated with the energy of x‐ray quanta. In spite of its quantum nature, Compton heating markedly affects the gas, forcing the matter outflow at x‐ray luminosities as small as three or four orders of magnitude less than the Eddington limit. The phenomenon of hot gas outflow takes place in the case of accretion on to a wind‐fed x‐ray source in a wide binary with massive OB or Be‐star. We propose a new spin‐down mechanism for accreting neutron stars that explains the existence of a number of long‐period (p∼100–1000 s) x‐ray ...

If gamma bursts are locally galactic, then the implied fluxes from a localized region of a neutron star surface are closed to the blackbody limit even at the extreme temperatures (of the order of 109 degrees) inferred from gamma‐burst spectra. One reasonable model is the accretion of an astroid or comet (Harwit and Salpeter 1973) onto a magnetized neutron star. What is frequently described as tidal disruption, instead becomes gravitational compression. Matter landing on a neutron star releases a specific energy density of several times c2/10. This energy density is ample to give rise to the inferred temperatures of 108 to 109 degrees. However, radiation stress greatly exceeds the gravitational stress even at the neutron star surface and a near instantaneous adiabatic expansion of the hot surface layers, cools them, and terminates the release of any high temperature radiation. The effective temperature of the radiation then becomes roughly the Eddington limit of 2×107 degrees. Only by the restraint of the ...