Radioisotopes Applied to Lubrication Problems of Inertial Gyro Bearings

Mayer, William J.; Lange, W. H.; Conners, T. F.

doi:10.1080/05698196308972005

Cited by 17 publications

(19 citation statements)

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“…7) the most luminous objects will be found at high values of initial disc mass and intermediate values of initial disc outer radius. 10 Recently, the direct collapse into a BH was proposed as an alternative way of forming SMBHs (Mayer et al 2010). It cannot, however, explain the observed strong luminosity dependence of the redshift at which the AGN space density peaks (see Section 1.1).…”

Section: S U M M a Ry A N D Discussionmentioning

confidence: 99%

The cosmogony of supermassive black holes

Duschl

Strittmatter

2011

Monthly Notices of the Royal Astronomical Society

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We report calculations of the evolution, under Reynolds viscosity, of the massive gaseous accretion discs thought to form in the centres of galaxies as a result of major galactic mergers at early epochs. Starting with the formation of such a disc and the postulated existence of a low‐mass ‘seed’ black hole, we focus on the mass accretion rate, , and hence luminosity, LGC, of a putative supermassive black hole (SMBH) in the galactic centre. Our computations cover a range of initial disc mass, Md, 0, and outer radius, smax, 0, and have been carried out under the assumption that cannot exceed the Eddington limit and that any excess mass supplied from the disc is lost from the system. Our purpose is to understand the extent to which such a model can account for the evolution with redshift of the observed properties of active galactic nuclei (AGNs). We show that within this framework: the initial mass supply rate from the disc increases with Md, 0 and compactness, adjusts rapidly (on a viscous time‐scale) to its peak value and decreases steadily thereafter; peak SMBH mass accretion rate and hence luminosity occurs when the (decreasing) disc flow rate equals the (increasing) black hole (BH) Eddington rate and is proportional to the BH mass, MEddBH, at that juncture; the fractional disc mass lost during the Eddington‐limited phase increases with Md, 0 and compactness so strongly that, for given (large) Md, 0, the peak BH luminosity and corresponding mass occurs for some intermediate value of smax, 0 so that MEddBH declines for more compact initial discs; SMBHs with mass MBH≥ 109 M⊙ and luminosity LGC≥ 3 × 1013 L⊙ can form in a time t < 109 yr as required by the most luminous high‐redshift quasi‐stellar objects but the Eddington‐induced mass‐loss renders unlikely the creation of BHs of comparable or greater mass or luminosity in significantly shorter times; the most luminous quasars form and die at the earliest epochs while those of lower luminosity occur over successively longer periods ranging up to the present time; in general, AGNs that are at an early evolutionary phase accrete at or close to their Eddington rate but evolve into the sub‐Eddington regime later on. The proposed scenario appears capable of accounting for many of the features of the observed quasar and AGN luminosity distribution with redshift and seems to be a natural consequence of the formation of massive central discs following major galaxy mergers.

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Section: S U M M a Ry A N D Discussionmentioning

confidence: 99%

The cosmogony of supermassive black holes

Duschl

Strittmatter

2011

Monthly Notices of the Royal Astronomical Society

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“…We include the contribution of both PopIII and PopII/I stars, with their chemical, mechanical and radiative feedback effects. We describe how we populate metal-free haloes with PopIII stars and briefly review the procedure adopted for haloes with Z > Z crit (see 1 It has been speculated that substantial inflows in major mergers can lead to massive BH seeds weighing more than 10 6 M (Mayer et al 2010).…”

Section: Introductionmentioning

confidence: 99%

High-redshift formation and evolution of central massive objects - II. The census of BH seeds

Devecchi

Volonteri

Rossi

et al. 2012

Monthly Notices of the Royal Astronomical Society

120

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We present results of simulations aimed at tracing the formation of nuclear star clusters (NCs) and black hole (BH) seeds in the framework of the current Λcold dark matter (ΛCDM) cosmogony. These BH seeds are considered to be progenitors of the supermassive BHs that inhabit today’s galaxies. We focus on two mechanisms for the formation of BHs at high redshifts: as end‐products of (1) Population III stars in metal‐free haloes, and (2) runaway stellar collisions in metal‐poor NCs. Our model tracks the chemical, radiative and mechanical feedback of stars on the baryonic component of the evolving haloes. This procedure allows us to evaluate when and where the conditions for BH formation are met, and to trace the emergence of BH seeds arising from the dynamical channel, in a cosmological context. BHs start to appear already at redshift ∼30 as remnants of Population III stars. The efficiency of this mechanism begins decreasing once feedbacks become increasingly important. Around redshift z∼ 15, BHs mostly form in the centre of mildly metal‐enriched haloes inside dense NCs. The seed BHs that form along the two pathways have at birth a mass of around 100–1000 M⊙. The occupation fraction of BHs is a function of both halo mass and mass growth rate: at a given redshift, heavier and faster growing haloes have a higher chance to form a native BH, or to acquire an inherited BH via merging of another system. With decreasing z, the probability of finding a BH shifts towards progressively higher mass halo intervals. This is due to the fact that, at later cosmic times, low‐mass systems rarely form a seed, and already formed BHs are deposited into larger mass systems due to hierarchical mergers. Our model predicts that at z= 0, all haloes above 1011 M⊙ should host a BH (in agreement with observational results), most probably inherited during their lifetime. Haloes less massive than 109 M⊙ have a higher probability to host a native BH, but their occupation fraction decreases below 10 per cent.

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“…First, there are active ongoing debates about when and how seed BHs form: either via a direct collapse of cold gas clouds leading to massive seeds of ∼10 4 -10 5 M (Loeb & Rasio 1994;Koushiappas, Bullock & Dekel 2004;Bellovary et al 2011;Volonteri & Stark 2011) or via stellar remnants from Population III stars, resulting in low-mass (∼100 M ) BH seeds (Madau & Rees 2001;Heger & Woosley 2002). An alternative possibility is direct seed formation in a merger event as seen in the numerical simulations of Mayer et al (2010). While the seeding mechanisms do not alter the AGN and BH population at low redshift (as gas accretion during the evolution exceeds the seed BH masses by many orders of magnitude), at high redshift the choice of the seeding model strongly influences the BH formation and is highly relevant for understanding the observed population of luminous high-redshift quasars.…”

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confidence: 99%

Origin of the antihierarchical growth of black holes

Hirschmann

Somerville

Naab

et al. 2012

Monthly Notices of the Royal Astronomical Society

120

142

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Observational studies have revealed a ‘downsizing’ trend in black hole (BH) growth: the number densities of luminous active galactic nuclei (AGN) peak at higher redshifts than those of faint AGN. This would seem to imply that massive BHs formed before low‐mass BHs, in apparent contradiction to hierarchical clustering scenarios. We investigate whether this observed ‘downsizing’ in BH growth is reproduced in a semi‐analytic model for the formation and evolution of galaxies and BHs, set within the hierarchical paradigm for structure formation. In this model, BHs evolve from light seeds (∼100 M⊙) and their growth is merger driven. The original Somerville et al. model (baseline model) reproduces the number density of AGN at intermediate redshifts and luminosities, but underproduces luminous AGN at very high redshift (z > 3) and overproduces them at low redshift (z < 1). In addition, the baseline model underproduces low‐luminosity AGN at low redshift (z < 1). In order to solve these problems, we consider several modifications to the physical processes in the model: (1) a ‘heavy’ BH seeding scenario; (2) a sub‐Eddington accretion rate ceiling that depends on the cold gas fraction and (3) an additional BH accretion mode due to disc instabilities. With these three modifications, the models can explain the observed downsizing, successfully reproduce the bolometric AGN luminosity function and simultaneously reproduce galaxy and BH properties in the local Universe. We also perform a comparison with the observed soft and hard X‐ray luminosity functions of AGN, including an empirical correction for torus‐level obscuration, and reach similar conclusions. Our best‐fitting model suggests a scenario in which disc instabilities are the main driver for moderately luminous Seyfert galaxies at low redshift, while major mergers are the main trigger for luminous AGN.

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Radioisotopes Applied to Lubrication Problems of Inertial Gyro Bearings

Cited by 17 publications

References 1 publication

The cosmogony of supermassive black holes

The cosmogony of supermassive black holes

High-redshift formation and evolution of central massive objects - II. The census of BH seeds

Origin of the antihierarchical growth of black holes

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