Measuring the Spins of Stellar Black Holes: A Progress Report

McClintock, J. E.; Narayan, Ramesh; Gou, Lingshan; Liu, J.; Penna, Robert F.; Steiner, James F.; Comastri, A.; Angelini, L.; Cappi, M.

doi:10.1063/1.3475156

Cited by 20 publications

(31 citation statements)

References 26 publications

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“…This conclusion is supported by observational evidence of the role of spin and accumulated magnetic flux in launching of relativistic jets both in microquasars and active galactic nuclei (see, e.g., [47][48][49][50][51]). …”

Section: A the Frameworksupporting

confidence: 59%

Extracting black-hole rotational energy: The generalized Penrose process

et al. 2014

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In the case involving particles the necessary and sufficient condition for the Penrose process to extract energy from a rotating black hole is absorption of particles with negative energies and angular momenta. No torque at the black-hole horizon occurs. In this article we consider the case of arbitrary fields or matter described by an unspecified, general energy-momentum tensor Tµν and show that the necessary and sufficient condition for extraction of a black hole's rotational energy is analogous to that in the mechanical Penrose process: absorption of negative energy and negative angular momentum. We also show that a necessary condition for the Penrose process to occur is for the Noether current (the conserved energy-momentum density vector) to be spacelike or past directed (timelike or null) on some part of the horizon. In the particle case, our general criterion for the occurrence of a Penrose process reproduces the standard result. In the case of relativistic jetproducing "magnetically arrested disks" we show that the negative energy and angular-momentum absorption condition is obeyed when the Blandford-Znajek mechanism is at work, and hence the high energy extraction efficiency up to ∼ 300% found in recent numerical simulations of such accretion flows results from tapping the black hole's rotational energy through the Penrose process. We show how black-hole rotational energy extraction works in this case by describing the Penrose process in terms of the Noether current.

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Section: A the Frameworksupporting

confidence: 59%

Extracting black-hole rotational energy: The generalized Penrose process

et al. 2014

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“…For instance, the highest spin black hole in Fig. 3 is GRS 1915+105, and the model for the soft X-ray spectrum of this object suggests a much smaller value of the spin a/r g ≈ 0.56 [6], than the one presented here (from [5]). Second, rapidly spinning black holes in Fig.…”

Section: Black Hole Spindown and Advanced Ligomentioning

confidence: 61%

“…3 we show the black hole Regge plot for two The regions in the black hole Regge plane affected by superradiance for the QCD axion with m = 3 · 10 −11 eV (the upper panel) and for a lighter axion with m = 10 −17 eV. The data points correspond to spin measurements obtained by fitting the thermal continuum X-ray spectra [5]. Old black holes are expected to be found in the shaded region, where they are not affected by superradiance.…”

Section: Introductionmentioning

confidence: 99%

“…Most crucially for what follows, recent advances in X-ray astronomy and in numerical magnetohydrodynamical simulations of the accreting gas in the Kerr metric open the possibility for a detailed exploration of the near-horizon region and, as a consequence, for high precision neasurements of black hole spins [3,4]. First estimates for the angular momentum of several black holes have already been delivered [5], often suggesting high values for the spin, although at the moment different techniques sometimes give rise to conflicting results [6].…”

Section: Introductionmentioning

confidence: 99%

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Exploring the string axiverse with precision black hole physics

2011

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It has recently been suggested that the presence of a plenitude of light axions, an Axiverse, is evidence for the extra dimensions of string theory. We discuss the observational consequences of these axions on astrophysical black holes through the Penrose superradiance process. When an axion Compton wavelength is comparable to the size of a black hole, the axion binds to the black hole "nucleus" forming a gravitational atom in the sky. The occupation number of superradiant atomic levels, fed by the energy and angular momentum of the black hole, grows exponentially. The black hole spins down and an axion Bose-Einstein condensate cloud forms around it. When the attractive axion self-interactions become stronger than the gravitational binding energy, the axion cloud collapses, a phenomenon known in condensed matter physics as "Bosenova". The existence of axions is first diagnosed by gaps in the mass vs spin plot of astrophysical black holes. For young black holes the allowed values of spin are quantized, giving rise to "Regge trajectories" inside the gap region. The axion cloud can also be observed directly either through precision mapping of the near horizon geometry or through gravitational waves coming from the Bosenova explosion, as well as axion transitions and annihilations in the gravitational atom. Our estimates suggest that these signals are detectable in upcoming experiments, such as Advanced LIGO, AGIS, and LISA. Current black hole spin measurements imply an upper bound on the QCD axion decay constant of 2 · 10 17 GeV, while Advanced LIGO can detect signals from a QCD axion cloud with a decay constant as low as the GUT scale. We finally discuss the possibility of observing the γ-rays associated with the Bosenova explosion and, perhaps, the radio waves from axion-to-photon conversion for the QCD axion.

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“…This status of affairs is due to the inability of detecting clean electromagnetic signals from the depths of the central engine and complexities involved in a first principles description of the underlying processes. Recently however, strong momentum has been gained at the observational level [2] (with further exciting opportunities via nearfuture VLBI observations, e.g. [3]) as well as in the theoretical front thanks to simulations of relevant systems, e.g.…”

Section: Introductionmentioning

confidence: 99%

Towards an understanding of the force-free magnetosphere of rapidly spinning black holes

2014

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The ability of a plasma surrounding spinning black holes to extract rotational energy and power energetic emissions has been recognized as a key astrophysical phenomenon. Important insights into the nature of this process are obtained through the analysis of the interplay between a force-free magnetosphere and the black hole. This task involves solving a complicated system of equations, often requiring complex numerical simulations. Recent analytical attempts at tackling this problem have exploited the fact that the near horizon region of extreme Kerr (NHEK) is endowed with an enhanced symmetry group. We continue in this direction and show that for some conformally selfsimilar solutions, the NHEK force-free equations reduce to a single non-linear ordinary differential equation which is difficult to solve with straightforward integration. We here introduce a new approach specifically tailored to this problem and describe how one can obtain physically meaningful solutions.

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Measuring the Spins of Stellar Black Holes: A Progress Report

Cited by 20 publications

References 26 publications

Extracting black-hole rotational energy: The generalized Penrose process

Extracting black-hole rotational energy: The generalized Penrose process

Exploring the string axiverse with precision black hole physics

Towards an understanding of the force-free magnetosphere of rapidly spinning black holes

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