Foundations of Black Hole Accretion Disk Theory

This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review, from a first-principles perspective, the physical processes at play in accretion disks. This leads us to the four primary accretion disk models that we review: Polish doughnuts (thick disks), Shakura-Sunyaev (thin) disks, slim disks, and advection-dominated accretion flows (ADAFs). After presenting the models we discuss issues of stability, oscillations, and jets. Following our review of the analytic work, we take a parallel approach in reviewing numerical studies of black hole accretion disks. We finish with a few select applications that highlight particular astrophysical applications: measurements of black hole mass and spin, black hole vs. neutron star accretion disks, black hole accretion disk spectral states, and quasi-periodic oscillations (QPOs).Comment: 91 pages, 23 figures, final published version available at http://www.livingreviews.org/lrr-2013-

The low-mass stellar population in the young cluster Tr37: Disk evolution, accretion, and environment

We present a study of accretion and protoplanetary disks around M-type stars in the 4 Myr-old cluster Tr37. With a well-studied solar-type population, Tr37 is a benchmark for disk evolution. We used low-resolution spectroscopy to identify 141 members (78 new) and 64 probable members, mostly M-type stars. H\alpha\ emission provides information about accretion. Optical, 2MASS, Spitzer, and WISE data are used to trace the SEDs. We construct radiative transfer models to explore the structures of full-disks, pre-transition, transition, and dust-depleted disks. Including the new and previously known members, we confirm that a substantial fraction (~2/5) of disks show signs of evolution, either as radial dust evolution (transition/pre-transition disks) or as a more global evolution (low small-dust masses, dust settling, and weak/absent accretion signatures). Accretion is strongly dependent on the SED type. About half of the transition objects are consistent with no accretion, and dust-depleted disks have weak (or undetectable) accretion signatures, especially among M-type stars. The analysis of accretion and disk structure suggests a parallel evolution of dust and gas. We find several distinct classes of evolved disks, based on SED type and accretion, pointing to different disk dispersal mechanisms and probably different evolutionary paths. Dust depletion and opening of inner holes appear to be independent processes: most transition disks are not dust-depleted, and most dust-depleted disks do not require inner holes. The differences in disk structure between M-type and solar-type stars in Tr37 (4 Myr) are not as remarkable as in the young, sparse, Coronet cluster (1-2 Myr), suggesting that other factors, like the environment/interactions, are likely to play a role in the disk evolution and dispersal. Finally, we also find some evidence of clumpy star formation or mini-clusters within Tr37.Comment: 21 pages, 16 figures, plus appendix with tables and figures. Accepted by A&

The radial structure of protostellar accretion disks: influence of jets

The radial structure of accretion disks is a fundamental issue regarding star and planet formation. Many theoretical studies, focussing on different aspects such as e.g. disk emissivity or ionization, have been conducted in the context of the Standard Accretion Disk (SAD) model, where no jet is present. We wish to calculate the structure of YSO accretion disks in an approach that takes into account the presence of the protostellar jets. The radial structure of these Jet Emitting Disks (JED) should then be compared to that of standard accretion disks. The analytical treatment used in this work is very similar to that of standard accretion disks but is using the parameter space of Magnetised Accretion-Ejection Structures that include the jet torque on the underlying disk. In this framework, the analytical expressions of key quantities, such as mid-plane temperatures, surface densities or disk aspect ratio are derived. It is found that JEDs present a structure very different from the SADs and that can be observationally tested. The implications on planet formation in the inner regions of accretion disks are briefly discussed. We also supply sets of analytical formulae, valid in different opacity regimes, for the disk quantities. These expressions can be readily used for any work where the disk structure is needed as an input for the model.Comment: 11 pages, 4 figures. Accepted for publication in A&

Massive Accretion Disks

Recent high resolution near infrared (HST-NICMOS) and mm-interferometric imaging have revealed dense gas and dust accretion disks in nearby ultra-luminous galactic nuclei. In the best studied ultraluminous IR galaxy, Arp 220, the 2 micron imaging shows dust disks in both of the merging galactic nuclei and mm-CO line imaging indicates molecular gas masses approx. 10^9 M_sun for each disk. The two gas disks in Arp 220 are counterrotating and their dynamical masses are approx. 2x10^9 M_sun, that is, only slightly larger than the gas masses. These disks have radii approx 100 pc and thickness 10-50 pc. The high brightness temperatures of the CO lines indicate that the gas in the disks has area filling factors of approx. 25-50% and mean densities of >~ 10^4 cm^(-3). Within these nuclear disks, the rate of massive star formation is undoubtedly prodigious and, given the high viscosity of the gas, there will also be high radial accretion rates, perhaps >~ 10 M_sun/yr. If this inflow persists to very small radii, it is enough to feed even the highest luminosity AGNs.Comment: LaTex, 6 pages with 1 postscript and 1 jpg figure, and 1 postscript table, To appear in the proc. of the Ringberg workshop on "Ultraluminous Galaxies: Monsters or Babies" (Ringberg castle, Sept. 1998), Ap&SS, in pres

Fragmentation of Massive Protostellar Disks

We examine whether massive-star accretion disks are likely to fragment due to self-gravity. Rapid accretion and high angular momentum push these disks toward fragmentation, whereas viscous heating and the high protostellar luminosity stabilize them. We find that for a broad range of protostar masses and for reasonable accretion times, massive disks larger than ~150 AU are prone to fragmentation. We develop an analytical estimate for the angular momentum of accreted material, extending the analysis of Matzner and Levin (2005) to account for strongly turbulent initial conditions. In a core-collapse model, we predict that disks are marginally prone to fragmentation around stars of about four to 15 solar masses -- even if we adopt conservative estimates of the disks' radii and tendency to fragment. More massive stars are progressively more likely to fragment, and there is a sharp drop in the stability of disk accretion at the very high accretion rates expected above 110 solar masses. Fragmentation may starve accretion in massive stars, especially above this limit, and is likely to create swarms of small, coplanar companions.Comment: 15 pages, 7 figures, accepted for publication in MNRAS, updated version with minor changes to tex

A Note on the Slim Accretion Disk Model

We show that when the gravitational force is correctly calculated in dealing with the vertical hydrostatic equilibrium of black hole accretion disks, the relationship that is valid for geometrically thin disks, i.e., $c_s/\Omega_K H =$ constant, where $c_s$ is the sound speed, $\Omega_K$ is the Keplerian angular velocity, and $H$ is the half-thickness of the disk, does not hold for slim disks. More importantly, by adopting the correct vertical gravitational force in studies of thermal equilibrium solutions, we find that there exists a maximally possible accretion rate for each radius in the outer region of optically thick accretion flows, so that only the inner region of these flows can possibly take the form of slim disks, and strong outflows from the outer region are required to reduce the accretion rate in order for slim disks to be realized.Comment: 14 pages, 5 figures, accepted by Ap

Nucleosynthesis in Advective Accretion Disks Around Galactic and Extra-Galactic Black Holes

We compute the nucleosynthesis of materials inside advective disks around black holes. We show that composition of incoming matter can change significantly depending on the accretion rate and accretion disks. These works are improvements on the earlier works in thick accretion disks of Chakrabarti, Jin & Arnett (1987) in presence of advection in the flow.Comment: Latex pages including figures. Kluwer Style files included. Appearing in `Observational Evidence for Black Holes in the Universe', ed. Sandip K. Chakrabarti, Kluwer Academic Publishers (DORDRECHT: Holland