Article

# The Spin of the Near-Extreme Kerr Black Hole GRS 1915+105

• ##### Li-Xin Li
The Astrophysical Journal (Impact Factor: 6.73). 06/2006; 652(1). DOI: 10.1086/508457
Source: arXiv

ABSTRACT Based on a spectral analysis of the X-ray continuum that employs a fully
relativistic accretion-disk model, we conclude that the compact primary of the
binary X-ray source GRS 1915+105 is a rapidly-rotating Kerr black hole. We find
a lower limit on the dimensionless spin parameter of a* greater than 0.98. Our
result is robust in the sense that it is independent of the details of the data
analysis and insensitive to the uncertainties in the mass and distance of the
black hole. Furthermore, our accretion-disk model includes an advanced
treatment of spectral hardening. Our data selection relies on a rigorous and
quantitative definition of the thermal state of black hole binaries, which we
used to screen all of the available RXTE and ASCA data for the thermal state of
GRS 1915+105. In addition, we focus on those data for which the accretion disk
luminosity is less than 30% of the Eddington luminosity. We argue that these
low-luminosity data are most appropriate for the thin alpha-disk model that we
employ. We assume that there is zero torque at the inner edge of the disk, as
is likely when the disk is thin, although we show that the presence of a
significant torque does not affect our results. Our model and the model of the
relativistic jets observed for this source constrain the distance and black
hole mass and could thus be tested by determining a VLBA parallax distance and
improving the measurement of the mass function. Finally, we comment on the
significance of our results for relativistic-jet and core-collapse models, and
for the detection of gravitational waves.

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##### Article: Humpy LNRF-velocity profiles in accretion discs orbiting almost extreme Kerr black holes. A possible relation to quasi-periodic oscillations
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ABSTRACT: Context: Change of sign of the LNRF-velocity gradient has been found for accretion discs orbiting rapidly rotating Kerr black holes with spin a>0.9953 for Keplerian discs and a>0.99979 for marginally stable thick discs. Such a "humpy" LNRF-velocity profiles occur just above the marginally stable circular geodesic of the black hole spacetimes. Aims: Aschenbach (2004) has identified the maximal rate of change of the orbital velocity within the "humpy" profile with a locally defined critical frequency of disc oscillations, but it has been done in a coordinate-dependent form that should be corrected. Methods: We define the critical "humpy" frequency νh in general relativistic, coordinate independent form, and relate the frequency defined in the LNRF to the distant observers. At radius of its definition, the resulting "humpy" frequency νh is compared to the radial νr and vertical νv epicyclic frequencies and the orbital frequency of the discs. We focus our attention to Keplerian thin discs and perfect-fluid slender tori where the approximation of oscillations with epicyclic frequencies is acceptable. Results: In the case of Keplerian discs, we show that the epicyclic resonance radii r3{:1} and r4{:1} (with ν_v{:}ν_r=3{:}1, 4{:}1) are located in vicinity of the "humpy" radius rh where efficient triggering of oscillations with frequencies νh could be expected. Asymptotically (for 1-a<10-4) the ratio of the epicyclic and Keplerian frequencies and the humpy frequency is nearly constant, i.e., almost independent of a, being for the radial epicyclic frequency ν_r{:}νh ˜ 3{:}2. In the case of thick discs, the situation is more complex due to dependence on distribution of the specific angular momentum ℓ determining the disc properties. For ℓ=const. tori and 1-a<10-6 the frequency ratios of the humpy frequency and the orbital and epicyclic frequencies are again nearly constant and independent of both a and ℓ being for the radial epicyclic frequency ν_r{:}νh close to 4. In the limiting case of very slender tori (ℓ˜ℓms) the epicyclic resonance radius r4{:1}˜ rh for all the relevant interval of 1-a<2× 10-4. Conclusions: .The hypothetical "humpy" oscillations could be related to the QPO resonant phenomena between the epicyclic oscillations in both the thin discs and marginally stable tori giving interesting predictions that have to be compared with QPO observations in nearly extreme Kerr black hole candidate systems. Generally, more than two observable oscillations are predicted.
Astronomy and Astrophysics 03/2007; 463(3):807-816. · 5.08 Impact Factor
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##### Article: Gravity Waves from Extreme-Mass-Ratio Plunges into Kerr Black Holes
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ABSTRACT: Massive objects orbiting a near-extreme Kerr black hole quickly plunge into the horizon after passing the innermost stable circular orbit. The plunge trajectory is shown to be related by a conformal map to a circular orbit. Conformal symmetry of the near-horizon region is then used to compute the gravitational radiation produced during the plunge phase.
03/2014;
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##### Article: Unified Field Theory and the Hierarchical Universe
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ABSTRACT: Everything from the smallest particle to the grand universe is constructed by Torque Grids. The grand structure of the universe is made up of infinite hierarchical Torque Grids; this theory falsifies Big Bang Theory (BBT) and Black Hole Theory. A Torque Grid is 10 -25 times smaller than an atom, and our universal Torque Grid size is 4.98 * 10 26 m. The Universe is timeless. The configuration of Spiral Arm Galaxy can also be explained by Unified Field Theory.
International Journal of Physics. 12/2013; 1(1):162-170.

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