Extracting Energy from a Black Hole through the Transition Region
TL;DR: In this article, a new scenario for extracting energy from a Kerr black hole is proposed, where magnetic field lines connecting plasma particles inside the ergosphere with remote loads are twisted so that energy and angular momentum are extracted from the plasma particles.
Abstract: A new scenario for extracting energy from a Kerr black hole is proposed. With magnetic field lines connecting plasma particles inside the ergosphere with remote loads, the frame dragging twists the field lines so that energy and angular momentum are extracted from the plasma particles. If the magnetic field is strong enough, the energy extracted from the particles can be so large that the particles have negative energy as they fall into the black hole. So, effectively, the energy is extracted from the black hole. The particles inside the ergosphere can be continuously replenished with accretion from a disk surrounding the black hole, so a transition region with a sufficient amount of plasma is formed between the black hole's horizon and the inner edge of the disk. Thus, the energy can be continuously extracted from the black hole through the transition region. This may be the most efficient way for extracting energy from a Kerr black hole: in principle, almost all of the rotational energy (up to ≈29% of the total energy of the black hole) can be extracted.
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TL;DR: In this paper, the authors consider an accretion flow model originally proposed by Bisnovatyi-Kogan and Ruzmaikin (1974), which has been confirmed in recent 3D MHD simulations.
Abstract: OAK-B135 We consider an accretion flow model originally proposed by Bisnovatyi-Kogan and Ruzmaikin (1974), which has been confirmed in recent 3D MHD simulations. In this model, the accreting gas drags in a strong poloidal magnetic field to the center such that the accumulated field disrupts the axisymmetric accretion flow at a relatively large radius. Inside the disruption radius, the gas accretes as discrete blobs or streams with a velocity much less than the free-fall velocity. Almost the entire rest mass energy of the gas is released as heat, radiation and mechanical/magnetic energy. Even for a non-rotating black hole, the efficiency of converting mass to energy is of order 50% or higher. The model is thus a practical analog of an idealized engine proposed by Geroch and Bekenstein.
480 citations
TL;DR: In this article, the authors analyzed the properties of the shallow decay segment in Swift XRT light curves and concluded that the observed shallow decay phase likely has diverse physical origins, likely a refreshed external shock.
Abstract: The origin of the shallow decay segment in Swift XRT light curves remains a puzzle. We analyze the properties of this segment with a sample of 53 long Swift GRBs detected before 2007 February. We show that the distributions of the sample's characteristics are lognormal or normal, and its isotropic X-ray energy (E(iso),X) is linearly correlated with the prompt gamma-ray energy but with a steeper photon spectrum, aside from some X-ray flashes. No significant spectral evolution is observed from this phase to the following phase, and the latter is usually consistent with external shock models, implying that the shallow decay is also of external-shock origin, likely a refreshed external shock. Within the refreshed-shock model, the data are generally consistent with a roughly constant injection luminosity up to the end of this phase, t(b). A positive correlation between Eiso; X and tb also favors this scenario. Among the 13 bursts that have well-sampled optical light curves, six have an optical break around tb and the breaks are consistent with being achromatic. However, the other seven either do not show an optical break or have a break at an epoch different from tb. This raises a concern for the energy injection scenario, suggesting that the optical and X-ray emission may not be the same component, at least for some bursts. There are four significant outliers in the sample, GRBs 060413, 060522, 060607A, and 070110. The shallow decay phase in these bursts is immediately followed by a very steep decay after tb, which is inconsistent with any external-shock model. The optical data for these bursts evolve independently from the X-ray data. These X-ray plateaus likely have an internal origin and demand continuous operation of a long-term central engine. We conclude that the observed shallow decay phase likely has diverse physical origins.
296 citations
TL;DR: In this article, the authors investigate the soft X-ray transients with black hole primaries, which may have been the sources of gamma-ray bursts (GRBs) and hypernovae earlier in their evolution.
Abstract: We investigate the soft X-ray transients with black hole primaries, which may have been the sources of gamma-ray bursts (GRBs) and hypernovae earlier in their evolution. For systems with evolved donors, we are able to reconstruct the pre-explosion periods and find that the black hole mass increases with the orbital period of the binary. This correlation can be understood in terms of angular momentum support in the helium star progenitor of the black hole, if the systems with shorter periods had more rapidly rotating primaries prior to their explosion; centrifugal support will then prevent more of its mass from collapsing into the black hole on a dynamical time. This trend of more rapidly rotating stars in closer binaries is usual in close binaries and in the present case can be understood in terms of spin-up during spiral-in and subsequent tidal coupling. We investigate the relation quantitatively and obtain reasonable agreement with the observed mass-period correlation. An important ingredient is the fact that the rapidly rotating new black hole powers both a GRB and the hypernova explosion of the remaining envelope, so that the material initially prevented from falling into the black hole will be expelled rather than accreted. For systems in which the donor is now and will remain in main sequence, we cannot reconstruct the pre-explosion period in detail, because some of their history has been erased by angular momentum loss through magnetic braking and gravitational waves. We can, however, show that their periods at the time of black hole formation were most likely 0.4-0.7 days, somewhat greater than their present periods. Furthermore, their black holes would have been expected to accrete ~1 M? of material from the donor during their previous evolution. Comparison with predictions suggests that little mass will be lost in the explosion for the relatively high pre-explosion periods of these binaries. A natural consequence of the He star rotation is that black holes formed in the shorter period (before explosion) soft X-ray transients acquire significant Kerr parameters. This makes them good sources of power for GRBs and hypernovae, via the Blandford-Znajek mechanism, and thus supports our model for the origin of GRBs in soft X-ray transients.
77 citations
TL;DR: The relativistic iron line prole observed by XMM-Newton in the spectrum of the Seyfert 1 galaxy MCG{6-30-15 (Wilms et al. 2001) is discussed in the framework of the lamp-post model as mentioned in this paper.
Abstract: The relativistic iron line prole recently observed by XMM-Newton in the spectrum of the Seyfert 1 galaxy MCG{6-30-15 (Wilms et al. 2001) is discussed in the framework of the lamp-post model. It is shown that the steep disc emissivity, the large line equivalent width and the amount of Compton reflection can be self-consistently reproduced in this scenario.
62 citations
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TL;DR: The year 2000 as discussed by the authors was a year in which some topics selected themselves as important through the sheer numbers of papers published, including the connection(s) between galaxies with active central engines and galaxies with starbursts, the transition from asymptotic giant branch stars to white dwarfs, gamma-ray bursters, solar data from three major satellite missions, and the cosmological parameters, including dark matter and very large scale structure.
Abstract: It was a year in which some topics selected themselves as important through the sheer numbers of papers published. These include the connection(s) between galaxies with active central engines and galaxies with starbursts, the transition from asymptotic giant branch stars to white dwarfs, gamma-ray bursters, solar data from three major satellite missions, and the cosmological parameters, including dark matter and very large scale structure. Several sections are oriented around processes - accretion, collimation, mergers, and disruptions - shared by a number of kinds of stars and galaxies. And, of course, there are the usual frivolities of errors, omissions, exceptions, and inventories.
60 citations
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TL;DR: This article derived expressions for the mass of a stationary axisymmetric solution of the Einstein equations containing a black hole surrounded by matter and for the difference in mass between two neighboring such solutions.
Abstract: Expressions are derived for the mass of a stationary axisymmetric solution of the Einstein equations containing a black hole surrounded by matter and for the difference in mass between two neighboring such solutions. Two of the quantities which appear in these expressions, namely the area A of the event horizon and the “surface gravity” κ of the black hole, have a close analogy with entropy and temperature respectively. This analogy suggests the formulation of four laws of black hole mechanics which correspond to and in some ways transcend the four laws of thermodynamics.
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TL;DR: In this article, a unified model of nuclear activity and a unified approach to infer the pressures, densities, and fluid velocities within jets are explained. But the model is not applicable to the case of relativistic radio sources.
Abstract: Powerful extragalactic radio sources comprise two extended regions containing magnetic field and synchrotron-emitting relativistic electrons, each linked by a jet to a central compact radio source located in the nucleus of the associated galaxy. These jets are collimated streams of plasma that emerge from the nucleus in opposite directions, along which flow mass, momentum, energy, and magnetic flux. Methods of using the observations diagnostically to infer the pressures, densities, and fluid velocities within jets are explained. The jets terminate in the extended radio components, where they interact strongly with the surrounding medium through a combination of shock waves and instabilities. Jets may expand freely, be confined by external gas pressure, or be pinched by toroidal magnetic fields. Shear flows are known to be Kelvin-Helmholtz unstable and thus may be responsible for some of the observed oscillation of jets about their mean directions and for creating the turbulence and shock waves needed to accelerate the relativistic electrons. Larger-scale bending may be caused by changes in the jet axis within the nucleus, gravitational interaction of the radio galaxy with a companion galaxy, or rapid motion of the source through dense intergalactic gas. The compact radio sources also exhibit a jet morphology and contain more direct clues as to the origins of jets; in particular, the variations sometimes observed imply bulk flows that are relativistic. It is widely believed that nuclear activity is ultimately ascribable to gas accreting onto a massive black hole. The accretion can proceed in several different fashions, depending upon whether or not the gas has angular momentum and whether or not the radiation emitted is sufficiently intense to influence the dynamics of the flow. Several distinct mechanisms for jet production in the context of black holes have been proposed. (Alternative mechanisms involving dense star clusters and massive spinning stars are also reviewed.) Supersonic jets may be collimated along the spin axis of a gas cloud surrounding the source of the lighter jet gas. Magnetic fields may be crucial in collimating jets, especially if they are wrapped around the jet by orbiting gas and can thereby collimate the outflow through the pinch effect. In fact, the spin energy of the black hole could also be extracted by magnetic torques, in which case the jet would contain electrons and positrons and carry a large electromagnetic Poynting flux. Statistical investigations of active galaxies also furnish valuable information on their nature and evolutionary behavior. The formation of particular kinds of sources appears to be correlated with environmental effects and cosmic epoch. In addition, the brightest compact radio sources on the sky, which probably involve relativistic motion, may be intrinsically faint objects beamed in our direction. There is now compelling evidence for the continuous fueling of extragalactic radio sources through jets emerging from the nucleus of the associated galaxy. The morphological classification of radio sources is interpreted in terms of the powers, speeds, and surroundings of jets. The ratio of the mass accretion rate to the mass of the hole may determine whether an active nucleus will be primarily a thermal object like an optical quasar or a nonthermal object like a radio galaxy. The authors outline a unified model of nuclear activity and assess what future progress may stem from observational developments (especially the proposed very long baseline array), experimental approaches (such as wind tunnel simulations), and theoretical studies (in particular, large-scale numerical hydrodynamical computing).
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