Article

# The spin of the near-extreme Kerr black hole GRS 1915+105

(Impact Factor: 6.28). 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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• "In considering non-BPS configurations, it is natural to seek a construction of gravitational solutions describing microstates of extremal, non-BPS black holes such as the extremal Kerr [9] and Myers-Perry [10] solutions. There is strong observational evidence of the existence of near-extremal black holes in our galaxy [11]. There has also been much interest in a recent conjecture that quantum gravity in the near-horizon region of an extremal Kerr black hole may be described by a chiral 2D CFT [12]. "
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ABSTRACT: The construction of neutral black hole microstates is an important problem, with implications for the information paradox. In this paper we conjecture a construction of non-supersymmetric supergravity solutions describing D-brane configurations which carry mass and angular momentum, but no other conserved charges. We first study a classical string solution which locally carries dipole winding and momentum charges in two compact directions, but globally carries no net winding or momentum charge. We investigate its backreaction in the D1-D5 duality frame, where this object becomes a supertube which locally carries oscillating dipole D1-D5 and NS1-NS5 charges, and again carries no net charge. In the limit of an infinite straight supertube, we find an exact supergravity solution describing this object. We conjecture that a similar construction may be carried out based on a class of two-charge non-supersymmetric D1-D5 solutions. These results are a step towards demonstrating how neutral black hole microstates may be constructed in string theory.
Journal of High Energy Physics 10/2013; 2014(4). DOI:10.1007/JHEP04(2014)072 · 6.22 Impact Factor
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• "For completeness, the velocity profile is given also for extreme black hole, demonstrating velocity jump at r = 1. by the humpy frequency, the radial (and vertical) epicyclic frequencies and their simple combinations taken at the common " humpy " radius, implying the black hole parameters of the source M = 14.8 M ⊙ , a=0.9998 [22], in good agreement with estimates given by different methods [6] [20]. This model can give interesting results also in the case of the X-ray binary system XTE J1650-500 [24], and an ULX candidate system NGC 5408 X-1. "
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ABSTRACT: We study the non-monotonic Keplerian velocity profiles related to locally non-rotating frames (LNRF) in the field of near-extreme braneworld Kerr black holes and naked singularities in which the non-local gravitational effects of the bulk are represented by a braneworld tidal charge \$b\$ and the 4D geometry of the spacetime structure is governed by the Kerr-Newman geometry. We show that positive tidal charge has a tendency to restrict the values of the black hole dimensionless spin \$a\$ admitting existence of the non-monotonic Keplerian LNRF-velocity profiles; the non-monotonic profiles exist in the black hole spacetimes with tidal charge smaller than \$b=0.41005\$ (and spin larger than \$a=0.76808\$). With decreasing value of the tidal charge (which need not be only positive), both the region of spin allowing the non-monotonicity in the LNRF-velocity profile around braneworld Kerr black hole and the velocity difference in the minimum-maximum parts of the velocity profile increase implying growing astrophysical relevance of this phenomenon.
Classical and Quantum Gravity 07/2011; 28(17). DOI:10.1088/0264-9381/28/17/175002 · 3.10 Impact Factor
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• "This correspondence has been extended to various exotic black holes in string theory, higher dimensional theories and gauged supergravities to name a few [48] [47] [49]. One of the main arguments of the Kerr/CFT correspondence is to apply the rich ideas of holographic duality to more astrophysical objects/black-holes, such as the nearly extremal GRS 1915+105, a binary black hole system 11000pc away in Aquila [50]. In [44] the authors show that GRS 1915+105 is holographically dual to a 2-dimensional chiral CFT with c L = (2±1)×10 79 and in the extremal limit the inner most stable circular orbit corresponds to the horizon. "
##### Article: Entropy and Temperature From Black-Hole/Near-Horizon-CFT Duality
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ABSTRACT: We construct a 2-dimensional CFT, in the form of a Liouville theory, in the near horizon limit of 4- and 3-dimensional black holes. The near horizon CFT assumes 2-dimensional black hole solutions first introduced by Christensen and Fulling and expanded to a greater class of black holes via Robinson and Wilczek. The 2-dimensional black holes admit a Diff(\$S^1\$) subalgebra, which upon quantization in the horizon limit becomes Virasoro with calculable central charge. This charge and lowest Virasoro eigen-mode reproduce the correct Bekenstein-Hawking entropy of the 4- and 3-dimensional black holes via the known Cardy formula. Furthermore, the 2-dimensional CFT's energy momentum tensor is anomalous. However, In the horizon limit the energy momentum tensor becomes holomorphic equaling the Hawking flux of the 4- and 3-dimensional black holes. This encoding of both entropy and temperature provides a uniformity in the calculation of black hole thermodynamic and statistical quantities for the non local effective action approach. Comment: 18 pages, references added, accepted in IOP's Classical and Quantum Gravity.
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