共查询到20条相似文献，搜索用时 62 毫秒
1.
《天文和天体物理学研究(英文版)》2016,(4)
The peaks in the spectra of the accretion disks surrounding massive black holes in quasars are in the far-UV or soft X-ray band, which are usually not observed. However, in the disk corona model, soft photons from the disk are Comptonized to high energy in the hot corona, and the hard X-ray spectra(luminosity and spectral shape) contain information on the incident spectra from the disk. The values of black hole spin parameter a*are inferred from the spectral fitting, which are spread over a large range, ~-0.94 to 0.998. We find that the inclination angles and mass accretion rates are well determined by the spectral fitting, but the results are sensitive to the accuracy of black hole mass estimates. No tight constraints on the black hole spins are achieved, if the uncertainties in black hole mass measurements are a factor of four,which are typical for the single-epoch reverberation mapping method. Recently, the accuracy of black hole mass measurement has been significantly improved to 0.2- 0.4 dex with the velocity resolved reverberation mapping method. The black hole spin can be well constrained if the mass measurement accuracy is50%. In the accretion disk corona scenario, a fraction of power dissipated in the disk is transported into the corona, and therefore the accretion disk is thinner than a bare disk for the same mass accretion rate,because the radiation pressure in the disk is reduced. We find that the thin disk approximation, H/R0.1,is still valid if 0.3 m 0.5, provided half of the dissipated power is radiated in the corona above the disk. 相似文献
2.
通过几十年的观测研究, 黑洞X射线双星(X-Ray Binary, XRB)部分特征被揭示. 然而, 吸积盘结构尚不确定. 黑洞XRB功率密度谱的截断频率与准周期振荡(Quasi Periodic Oscillation, QPO)的相关性质(W-K关系)可以限制吸积盘结构. 利用慧眼-HXMT (Hard X-ray Modulation Telescope)观测到的5个黑洞XRB的数据, 对黑洞XRB的W-K关系进行了研究, 结果表明在慧眼-HXMT观测的3个探测器能段中W-K关系成立. 此外在MAXI J1535-571之中存在截断频率和吸积盘内半径的相关关系, 这和截断的吸积盘结构一致. 如果观测到的功率密度谱来自质量吸积率的扰动传播, 可以推测吸积盘内半径接近最内圆形稳定轨道, 此黑洞可能是高自旋系统. 相似文献
3.
具有不同质量的恒星在耗尽其热核能源后,最终可能会坍缩成为性质完全不同的致密天体,如白矮星、中子星或者黑洞。从20世纪30年代起,黑洞的观测及其证认一直是天体物理学的研究热点之一。首先简要地回顾了恒星级黑洞的形成及其候选天体的研究历史;然后介绍了如何从观测上证认恒星级黑洞:接着详细讨论了恒星级黑洞的质量和自转参数的测量方法;最后介绍恒星级黑洞观测及其证认的最新研究进展,并做出结论:目前已经有充分的证据宣告在部分吸积X射线双星中存在恒星级黑洞。 相似文献
4.
汪定雄 《中国天文和天体物理学报》1996,(4)
本文详细讨论了在Blandford－Znajek过程中吸积盘中心黑洞的角动量和质量的总变化率与质量吸积率和能量提取率之比的关系，在此基础上讨论了BlandfordZnajek过程对黑洞吸积盘内边缘半径r_(ms)演化的影响，并证明在此过程中中心黑洞的熵总是增大的。 相似文献
5.
Raines SN Watson DM Pipher JL Forrest WJ Greenhouse MA Satyapal S Woodward CE Smith HA Fischer J Goetz JA Frank A 《The Astrophysical journal》2000,533(2):L115-L118
When some magnetic field lines connect a Kerr black hole with a disk rotating around it, energy and angular momentum are transferred between them. If the black hole rotates faster than the disk, ca&solm0;GMH>0.36 for a thin Keplerian disk, then energy and angular momentum are extracted from the black hole and transferred to the disk (MH is the mass and aMH is the angular momentum of the black hole). This way, the energy originating in the black hole may be radiated away by the disk. The total amount of energy that can be extracted from the black hole spun down from ca&solm0;GMH=0.998 to ca&solm0;GMH=0.36 by a thin Keplerian disk is approximately 0.15MHc2. This is larger than approximately 0.09MHc2, which can be extracted by the Blandford-Znajek mechanism. 相似文献
6.
E. Churazov R. Sunyaev W. Forman H. Böhringer 《Monthly notices of the Royal Astronomical Society》2002,332(3):729-734
The assumption that radiative cooling of gas in the centres of galaxy clusters is approximately balanced by energy input from a central supermassive black hole implies that the observed X-ray luminosity of the cooling flow region sets a lower limit on active galactic nucleus (AGN) mechanical power. The conversion efficiency of the mechanical power of the AGN into gas heating is uncertain, but we argue that it can be high even in the absence of strong shocks. These arguments inevitably lead to the conclusion that the time-averaged mechanical power of AGNs in cooling flows is much higher than the bolometric luminosity of these objects observed currently.
The energy balance between cooling losses and AGN mechanical power requires some feedback mechanism. We consider a toy model in which the accretion rate on to a black hole is set by the classic Bondi formula. Application of this model to the best studied case of M87 suggests that accretion proceeds at approximately the Bondi rate down to a few gravitational radii with most of the power (at the level of a few per cent of the rest mass) being carried away by an outflow. 相似文献
The energy balance between cooling losses and AGN mechanical power requires some feedback mechanism. We consider a toy model in which the accretion rate on to a black hole is set by the classic Bondi formula. Application of this model to the best studied case of M87 suggests that accretion proceeds at approximately the Bondi rate down to a few gravitational radii with most of the power (at the level of a few per cent of the rest mass) being carried away by an outflow. 相似文献
7.
黑洞的吸积是天体物理学中最重要的基础理论之一。近年来该理论取得了引人瞩目的重大进展,具体表现在两个方面。其一是根据黑洞吸积必定跨声速这一特性,提出在一定条件下吸积流中会出现激波,这可称为含激波的吸积理论;其二是基于对一种局域致冷机制-贮导（advection）致冷的作用的重新认识而建立的,称为ADAF理论。在吸积盘的光学厚度很小或很大两种情况下,粘滞产生的大部分热量没有像在标准薄盘模型中那样辐射出去,而是贮存在流体中随流体的径向运动进入黑洞。与标准薄盘模型相比,贮导吸积盘具有高得多的温度和大得多的径向速度,但角动量小于开普勒角动量,吸积致能的效率要低得多。 相似文献
8.
Z. Y. Wang P. J. Chen D. X. Wang L. Y. Zhang 《Journal of Astrophysics and Astronomy》2013,34(1):33-40
In this paper, we use a Langevin type equation with a damping term and stochastic force to describe the stochastic oscillations on the vertical direction of the accretion disk around a black hole, and calculate the luminosity and power spectral density (PSD) for an oscillating disk. Then we discuss the stochastic resonance (SR) phenomenon in PSD curves for different parameter values of viscosity coefficient, accretion rate, mass of black hole and outer radius of the disk. The results show that our simulated PSD curves of luminosity for disk oscillation have the same profile as the observed PSD of black hole X-ray binaries (BHXBs) in the lowhard state, and the SR of accretion disk oscillation may be an alternative interpretation of the persistent low-frequency quasi-periodic oscillations (LFQPOs). 相似文献
9.
The stability of the innermost disk region orbiting a Kerr black hole is investigated for geometrically thin accretion disks. The infalling matter transports mass and angular momentum into the Kerr hole. This affects the inner disk boundary and leads to runaway instabilities in some cases. 相似文献
10.
N. A. Silant’ev M. Yu. Piotrovich Yu. N. Gnedin T. M. Natsvlishvili 《Astronomy Letters》2010,36(8):549-553
We compare two methods for estimating the magnetic field near a black hole—based on a statistical formula that relates the
magnetic field on the horizon of the black hole to its mass and on a direct magnetic field determination from optical polarimetric
observations. An optically thick magnetized accretion disk is usually formed around the black hole in active galactic nuclei.
The linear polarization of the radiation emerging from the disk is related to the local magnetic field and the polarization
in Milne’s classical problem. The magnetic field in the region from where the radiation with the observed wavelength comes
can be estimated by measuring this polarization. On the other hand, this field can be estimated from the above statistical
formula if the field near the black hole is extrapolated into the accretion disk using a standard power law. Comparison of
the magnetic field obtained from the observed polarization with the extrapolated field can serve to estimate the accuracy
of the latter and the exponent in the adopted extrapolation law. As an example, we compare these two methods for the source
NGC 4258. 相似文献
11.
We briefly review recent developments in black hole accretion disk theory, emphasizing the vital role played by magnetohydrodynamic
(MHD) stresses in transporting angular momentum. The apparent universality of accretion-related outflow phenomena is a strong
indicator that large-scale MHD torques facilitate vertical transport of angular momentum. This leads to an enhanced overall
rate of angular momentum transport and allows accretion of matter to proceed at an interesting rate. Furthermore, we argue
that when vertical transport is important, the radial structure of the accretion disk is modified at small radii and this
affects the disk emission spectrum. We present a simple model demonstrating how energetic, magnetically-driven outflows modify
the emergent disk emission spectrum with respect to that predicted by standard accretion disk theory. A comparison of the
predicted spectra against observations of quasar spectral energy distributions suggests that mass accretion rates inferred
using the standard disk model may be severely underestimated. 相似文献
12.
A. S. Zentsova 《Astrophysics and Space Science》1983,95(2):459-462
A hypothesis is being put forward that the formation of jets in the nuclei of radio galaxies is due to a high-speed energy excretion (explosion) in the accretion disk around a massive black hole. The explosion can be induced, for example, by a fall of the star into the black hole. For the accretion disk featuring an exponential high-density distribution, an asymmetrical explosion can be obtained: the shock front moves in the direction of decreasing the density accelerately and achieves the relativistic velocity swiftly, carrying away the most fraction of the explosion energy. Radio emission of the jet involves synchrotron radiation of relativistic electrons which are accelerated by such shock wave in the magnetic field driven up by the shock front. 相似文献
13.
The normal mode oscillations of thin accretion disks around black holes and other compact objects are analyzed and contrasted with those in stars. For black holes, the most robust modes are gravitationally trapped near the radius at which the radial epicyclic frequency is maximum. Their eigenfrequencies depend mainly on the mass and angular momentum of the black hole. The fundamental g-mode has recently been seen in numerical simulations of black hole accretion disks. For stars such as white dwarfs, the modes are trapped near the inner boundary (magnetospheric or stellar) of the accretion disk. Their eigenfrequencies are approximately multiples of the (Keplerian) angular velocity of the inner edge of the disk. The relevance of these modes to the high frequency quasi-periodic oscillations observed in the power spectra of accreting binaries will be discussed. In contrast to most stellar oscillations, most of these modes are unstable in the presence of viscosity (if the turbulent viscosity induced by the magnetorotational instability acts hydrodynamically). 相似文献
14.
We apply the disk-corona evaporation model (Meyer & Meyer-Hofmeister) originally derived for dwarf novae to black hole systems. This model describes the transition of a thin cool outer disk to a hot coronal flow. The mass accretion rate determines the location of this transition. For a number of well-studied black hole binaries, we take the mass flow rates derived from a fit of the advection-dominated accretion flow (ADAF) model to the observed spectra (for a review, see Narayan, Mahadevan, & Quataert) and determine where the transition of accretion via a cool disk to a coronal flow/ADAF would be located for these rates. We compare this with the observed location of the inner disk edge, as estimated from the maximum velocity of the Halpha emission line. We find that the transition caused by evaporation agrees with this determination in stellar disks. We also show that the ADAF and the "thin outer disk + corona" are compatible in terms of the physics in the transition region. 相似文献
15.
《New Astronomy》2015
We derive here a relatively simple expression for the total wind mass loss rates in QSOs within the accretion disk wind scenario. We show that the simple expression derived here for QSO disk wind mass loss rate is in a very good agreement with the more “exact” values obtained through significantly more complex and detailed numerically intensive 2.5D time-dependent simulations. Additionally we show that for typical QSO parameters, the disk itself will be emitting mostly in the UV/optical spectrum, in turn implying that the X-ray emission from QSOs likely is produced through some physical mechanism acting at radii smaller than the inner disk radius (for a standard accretion disk, half of the initially gravitational potential energy of the accreting disk mass is emitted directly by the disk, while the other half “falls” closer towards the black hole than the inner disk radius). We also show that for typical QSO parameters, the disk itself is dominated by continuum radiation pressure (rather than thermal pressure), resulting in a “flat disk” (except for the innermost disk regions). 相似文献
16.
采用等效电路模型讨论了两种不同类型的磁场对黑洞的旋转能量和角动量的提取机制；Blandford-Znajek(BZ)过程和磁耦合过程，在研究磁化吸积盘中心黑洞自转参量演化特征的基础上，详细比较了纯吸积过程，BZ过程和磁耦合过程对黑洞吸积盘放能效率的贡献，结果表明，磁耦合过程是提取黑洞旋转能量重要的新机制，其放能效率与BZ过程几乎相等，在黑洞自转不是特别大的情况，纯吸积过程的放能效率高于BZ过程和磁耦合过程的放能效率，但是当黑洞自转接近极端Kerr黑洞的自转状态时，放能效率主要由BZ过程和磁耦合过程贡献。 相似文献
17.
Hydrodynamic simulations of the merger of stellar mass black hole-neutron star binaries are compared with mergers of binary neutron stars. The simulations are Newtonian but take into account the emission and back-reaction of gravitational waves. The use of a physical nuclear equation of state allows us to include the effects of neutrino emission. For low neutron star-to-black hole mass ratios, the neutron star transfers mass to the black hole during a few cycles of orbital decay and subsequent widening before finally being disrupted, whereas for ratios near unity the neutron star is destroyed during its first approach. A gas mass between approximately 0.3 and approximately 0.7 M middle dot in circle is left in an accretion torus around the black hole and radiates neutrinos at a luminosity of several times 1053 ergs s-1 during an estimated accretion timescale of about 0.1 s. The emitted neutrinos and antineutrinos annihilate into e+/- pairs with efficiencies of 1%-3% and rates of up to approximately 2x1052 ergs s-1, thus depositing an energy Enunu&d1; less, similar1051 ergs above the poles of the black hole in a region that contains less than 10-5 M middle dot in circle of baryonic matter. This could allow for relativistic expansion with Lorentz factors around 100 and is sufficient to explain apparent burst luminosities Lgamma approximately Enunu&d1;&solm0;&parl0;fOmegatgamma&parr0; up to several times 1053 ergs s-1 for burst durations tgamma approximately 0.1-1 s, if the gamma emission is collimated in two moderately focused jets in a fraction fOmega=2deltaOmega&solm0;&parl0;4pi&parr0; approximately 1&solm0;100-(1/10) of the sky. 相似文献
18.
Orhan Dönmez 《Astrophysics and Space Science》2006,305(2):187-196
In this paper, perturbations of an accretion disk by a star orbiting around a black hole are studied. We report on a numerical experiment, which has been carried out by using a parallel-machine code originally developed by Dönmez (2004). An initially steady state accretion disk near a non-rotating (Schwarzschild) black hole interacts with a “star”, modeled as an initially circular region of increased density. Part of the disk is affected by the interaction. In some cases, a gap develops and shock wave propagates through the disk. We follow the evolution for order of one dynamical period and we show how the non-axisymetric density perturbation further evolves and moves downwards where the material of the disk and the star become eventually accreted onto the central body. When the star perturbs the steady state accretion disk, the disk around the black hole is destroyed by the effect of perturbation. The perturbed accretion disk creates a shock wave during the evolution and it loses angular momentum when the gas hits on the shock waves. Colliding gas with the shock wave is the one of the basic mechanism of emitting the X-rays in the accretion disk. The series of supernovae occurring in the inner disk could entirely destroy the disk in that region which leaves a more massive black hole behind, at the center of galaxies. 相似文献
19.
On the basis of the equivalent circuit model, we investigate two different mechanisms of extracting energy of rotation and angular momentum from a black hole by magnetic field, namely, the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process. The contributions to the efficiency of energy release via pure accretion process, BZ process and MC process are compared in detail by studying the evolutionary characteristics of the spin parameter of the black hole at the center of the magnetized accretion disk. It is shown that the MC process is an important new mechanism of extracting energy from the rotating black hole and its efficiency of energy release is almost as high as that of the BZ process. The efficiency of energy release via pure accretion process is higher than those of BZ process and magnetic coupling process. However, when the rotation of a black hole approaches that of an extreme Kerr black hole,the efficiency of energy release is mainly due to the contributions of BZ process and MC process. 相似文献
20.
High-frequency quasi-periodic variations (HF QPOs) in the X-ray light curves of black hole X-ray novae can be understood as
oscillations of the accretion disk in a nonlinear 3:2 resonance. An m = 0 vertical oscillation near a black hole modulates the X-ray emission through gravitational lensing (light-bending) at
the source. Certain oscillations of the accretion disk will also modulate the mass accretion rate, and in neutron-star systems
this would lead to nearly periodic variations in brightness of the luminous boundary layer on the stellar surface – the amplitude
of the neutron-star HF QPOs would be thus increased relative to the black hole systems.
The “kHz QPOs” in black holes are in the hecto-Hz range. 相似文献