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781.
782.
E. H. Dowdye 《Astronomische Nachrichten》2007,328(2):186-191
Intense observations of the galactic center since 1992 have revealed the presence of a supermassive object located there, some 26 000 light years from Earth. The mass of the galactic center was determined using time resolved astrometry over a time span of 13 years, from 1992 to present. The observations clearly show that the stars in the immediate vicinity of the supermassive galactic center, denoted as Sagittarius A* (Sgr A*), move along purely Keplerian orbits around Str A*. Observation of the rapidly moving stars permitted astrophysicists to determine a mass for the galactic center of around 3.6 million solar masses. Time resolved images of the Keplerian motions of these stars has exhibited to date no evidence of distortions in the images due to gravitational light bending effects, as predicted by General Relativity. In this paper, a well known tool commonly used by astrophysicists for estimating the effect of gravitation on light rays was examined. The results reveal flaws in the understanding of fundamental principles in mathematical physics applied to gravitational effects on rays of light, as predicted by General Relativity, at the site of a point‐like gravitating masses such as the galactic center mass. Application of the Gauss Law to point‐like gravitating masses shows that a requirement for the colinear alignment of the light source, the lensing and the observer is not necessary for an observation of gravitational lensing as predicted by General Relativity. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
783.
Y. Lu K. S. Cheng L. T. Yang L. Zhang 《Monthly notices of the Royal Astronomical Society》2000,314(3):453-458
We investigate the runaway instability of configurations consisting of a massive dense but non-self-gravitating thick disc/torus surrounding a massive black hole (MBH). We limit our model parameters to values that result in a self-consistent thick disc around an MBH. We identify, analytically, the index of the angular momentum distribution that will form a thick disc as an initial equilibrium state, and obtain the mass ratio of the disc to the central black hole for which the disc is dominated by the radiation pressure. In our theoretical framework we find that a self-consistent thick disc with constant angular momentum leads to a runaway instability on a dynamical time-scale. However, even a slight increase of the specific angular momentum outwards has a strong stabilizing effect on the accretion process. Finally, we discuss our results and present possible applications to high-energy emission. 相似文献
784.
J. O. Stenflo 《Journal of Astrophysics and Astronomy》2000,21(3-4):451-457
This summary lecture makes no attempt to summarize what was actually said at the meeting, since this is well covered by the
other contributors. Instead I have structured my presentation in three parts: First I try to demonstrate why the Sun is unique
by comparing it with laboratory plasmas. This is followed by some personal reminiscences that go back a significant fraction
of the century. I conclude in the form of a poem about this memorable conference in honor of the centennial anniversary of
the Kodaikanal Observatory. 相似文献
785.
E. M. Drobyshevski 《Monthly notices of the Royal Astronomical Society》2000,311(3):L1-L3
We start from the hypothesis that the dark matter of the Galactic disc contains Planckian particles carrying a negative electric charge of up to Z =10, which we call dark electric matter objects (daemons). Daemons are capable of catalysing proton-fusion reactions, which may account for the observed solar neutrino deficiency. The inevitable poisoning of the catalytic property of daemons as they capture heavy nuclei ( A 20) in the interior of the Sun is used to estimate the decay time of a daemon-containing nucleus (nucleon) in quantum-relativistic processes, which remain largely unknown. This time is τ ex ∼10−7 s. This may mean that the lower limit on the mass of an intranucleonic particle interacting with a daemon is ∼108 –1010 GeV and, possibly, even ∼1014 –1015 GeV. The desirability of a search for multiple events occurring with an interval ∼ τ ex along the 'slow' daemon trajectories on operating installations dedicated to detection of the proton decay is pointed out. 相似文献
786.
M. A. Nowak 《Monthly notices of the Royal Astronomical Society》2000,318(2):361-367
Among the variability behaviours exhibited by neutron star systems are the so-called 'horizontal branch oscillations' (HBO, with frequencies ≈50 Hz), the 'lower-frequency kHz quasi-periodic oscillation' (QPO) and the 'upper-frequency kHz QPO', with the latter two features being separated in frequency by an amount comparable to, but varying slightly from, the suspected spin-frequency of the neutron star. Recently, Psaltis, Belloni & van der Klis have suggested that there exists a correlation between these three frequencies that, when certain identifications of variability features are made, even encompasses black hole sources. We consider this hypothesis by reanalysing a set of GX 339−4 observations. The power spectral density (PSD) constructed from a composite of seven separate, but very similar, observations shows evidence for three broad peaks in the PSD. If the peak frequencies of these features are identified with QPO, then their frequencies approximately fit the correlations suggested by Psaltis, Belloni, & van der Klis. We also reanalyse a Cyg X-1 observation and show that the suggested QPO correlation may also hold, but that complications arise when the QPOs (which, in reality, are fairly broad features) are considered as a function of energy band. These fits suggest the existence of at least three separate, independent physical processes in the accretion flow, a hypothesis that is also supported by consideration of the Fourier frequency-dependent time lags and coherence function between variability in different energy bands. If these variability features have a common origin in neutron star and black hole systems, then 'beat frequency models' of kHz QPO in neutron star systems are called into question. 相似文献
787.
788.
A. R. King 《Monthly notices of the Royal Astronomical Society》2000,312(3):L39-L41
I show that the Eddington limit implies a critical orbital period P crit (BH)≃2 d beyond which black hole LMXBs cannot appear as persistent systems. The unusual behaviour of GRO J1655–40 may result from its location close to this critical period. 相似文献
789.
790.