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991.
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993.
Fazeleh Khajenabi Mohsen Shadmehri 《Monthly notices of the Royal Astronomical Society》2007,377(4):1689-1695
We study the dynamical structure of a self-gravitating disc with coronae around a supermassive black hole. Assuming that the magnetorotational instability responsible for generating the turbulent stresses inside the disc is also the source for a magnetically dominated corona, a fraction of the power released when the disc matter accretes is transported to and dissipated in the corona. This has a major effect on the structure of the disc and its gravitational (in)stability according to our analytical and self-consistent solutions. We determine the radius where the disc crosses the inner radius of gravitational instability and forms the first stars. Not only the location of this radius which may extend to very large distances from the central black hole, but also the mass of the first stars highly depends on the input parameters, notably the viscosity coefficient, the mass of the central object and the accretion rate. For accretion discs around quasi-stellar objects (QSOs) and the Galactic Centre, we determine the self-gravitating radius and the mass of the first clumps. Comparing the cases with a corona and without a corona for typical discs around QSOs or the Galactic Centre, when the viscosity coefficient is around 0.3, we show that the self-gravitating radius decreases by a factor of approximately 2, but the mass of the fragments increases with more or less the same factor. The existence of a corona implies a more gravitationally unstable disc according to our results. The effect of a corona on the instability of the disc is more effective when the viscosity coefficient increases. 相似文献
994.
David L. Meier 《Astrophysics and Space Science》2005,300(1-3):55-65
In this paper I propose that the inner part of a black hole accretion inflow (< 100 rg) may enter a magnetically dominated, magnetosphere-like phase in which the strong, well-ordered fields play a more important
role than weak, turbulent fields. In the low/hard state this flow is interior to the standard ADAF usually invoked to explain
the observed hot, optically thin emission. Preliminary solutions for these new MDAFs are presented.
Time-dependent X-ray and radio observations give considerable insight into these processes, and a new interpretation of the
X-ray power spectrum (as arising from many disk radii) may be in order. While an evaporative ADAF model explains the noise
power above 0.01 Hz, an inner MDAF is needed to explain the high-frequency cutoff near 1 Hz, the presence of a QPO, and the
production of a jet. The MDAF scenario also is consistent with the phenomonological models presented at this meeting by several
authors. 相似文献
995.
Ana Inés Gómez de Castro 《Astrophysics and Space Science》2006,302(1-4):1-2
Protons of energy 109 GeV and 104 GeV accelerating by the magnetic field of very strongly magnetized neutron stars and of extreme Kerr-Newmann black holes
(respectively) may undergo instantaneous decay. 相似文献
996.
997.
998.
The impact of cosmic dust on supernova cosmology 总被引:1,自引:0,他引:1
Pier Stefano Corasaniti 《Monthly notices of the Royal Astronomical Society》2006,372(1):191-198
999.
The current paradigm of high energy spectroscopy tells us that light emitted from a wide variety of objects has its origin
close to the black hole event horizon. As such, these photons are subject to general relativistic effects such as light-bending,
gravitational lensing and redshift, time-dilation, etc. These gravitational effects are well-understood from a theoretical
standpoint and therefore, provide a natural mechanism to test the properties of strong gravitational fields. To this end,
we have developed a new (semi-analytic) strong gravity code, capable of describing the contribution of photons that perform
multiple orbits of the hole. We apply this code to a simple Keplerian accretion disk in order to understand the role played
by the angular emissivity, black hole spin and higher order images in forming the line profile. 相似文献
1000.
We study the chaotic motions in the field of two fixed black holes M1, M2 by calculating (a) the asymptotic curves from the main unstable periodic orbits, (b) the asymptotic orbits, with particular emphasis οn the homoclinic and heteroclinic orbits, and (c) the basins of attraction of the two black holes. The orbits falling on M1and M2form fractal sets. The asymptotic curves consist of many arcs, separated by gaps. Every gap contains orbits falling on a black hole. The sizes of various arcs decrease as the mass ofM1 increases. The basins of attraction of the black holes M1, M2consist of large compact regions and of thin filaments. The relative area of the basin M2 tends to 100 as M1 → 0, and it decreases as M1 increases. The total area of the basins is found analytically, while the relative area of the basin M2 is given by an empirical formula. Further empirical formulae give the exponential decrease of the number of asymptotic orbits that have not yet reached a black hole after n iterations. 相似文献