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71.
Ipsita Mandal Arnab K. Ray Tapas K. Das 《Monthly notices of the Royal Astronomical Society》2007,378(4):1400-1406
The stationary, spherically symmetric, polytropic and inviscid accretion flow in the Schwarzschild metric has been set-up as an autonomous first-order dynamical system, and it has been studied completely analytically. Of the three possible critical points in the flow, the one that is physically realistic behaves like the saddle point of the standard Bondi accretion problem. One of the two remaining critical points exhibits the strange mathematical behaviour of being either a saddle point or a centre-type point, depending on the values of the flow parameters. The third critical point is always unphysical and behaves like a centre-type point. The treatment has been extended to pseudo-Schwarzschild flows for comparison with the general relativistic analysis. 相似文献
72.
Alister W. Graham 《Monthly notices of the Royal Astronomical Society》2007,379(2):711-722
The differing M bh – L relations presented in McLure & Dunlop, Marconi & Hunt and Erwin et al. have been investigated. A number of issues have been identified and addressed in each of these studies, including but not limited to the removal of a dependency on the Hubble constant, a correction for dust attenuation in the bulges of disc galaxies, the identification of lenticular galaxies previously treated as elliptical galaxies and the application of the same ( Y ∣ X ) regression analysis. These adjustments result in relations which now predict similar black hole masses. The optimal K -band relation is log( M bh /M⊙ ) =−0.37(±0.04)( M K + 24) + 8.29(±0.08) , with a total (not intrinsic) scatter in log M bh equal to 0.33 dex. This level of scatter is similar to the value of 0.34 dex from the relation of Tremaine et al. and compares favourably with the value of 0.31 dex from the M bh – n relation of Graham & Driver. Using different photometric data, consistent relations in the B and R band are also provided, although we do note that the small ( N = 13) R -band sample used by Erwin et al. is found here to have a slope of −0.30 ± 0.06. Performing a symmetrical regression on the larger K -band sample gives a slope of ∼−0.40, implying M bh ∝ L 1.00 . Implications for galaxy–black hole co-evolution, in terms of dry mergers, are briefly discussed, as are the predictions for intermediate mass black holes. Finally, as noted by others, a potential bias in the galaxy sample used to define the M bh – L relations is shown and a corrective formula provided. 相似文献
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Shock oscillation model for quasi-periodic oscillations in stellar mass and supermassive black holes
T. Okuda V. Teresi D. Molteni 《Monthly notices of the Royal Astronomical Society》2007,377(4):1431-1438
We numerically examine centrifugally supported shock waves in 2D rotating accretion flows around a stellar mass (10 M⊙ ) and a supermassive (106 M⊙ ) black holes over a wide range of input accretion rates of . The resultant 2D shocks are unstable with time and the luminosities show quasi-periodic oscillations (QPOs) with modulations of a factor of 2–3 and with periods of a tenth of a second to several hours, depending on the black hole masses. The shock oscillation model may explain the intermediate frequency QPOs with 1–10 Hz observed in the stellar mass black hole candidates and also suggest the existence of QPOs with the period of hours in active galactic nuclei. When the accretion rate is low, the luminosity increases in proportion to the accretion rate. However, when greatly exceeds the Eddington critical rate , the luminosity is insensitive to the accretion rate and is kept constantly around ∼3 L E . On the other hand, the mass-outflow rate increases in proportion to and it amounts to about a few per cent of the input mass-flow rate. 相似文献