共查询到18条相似文献，搜索用时 875 毫秒
1.
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
2.
黑洞吸积被认为是活动星系核的能量来源,而研究黑洞吸积最主要的难题是要解释吸积气体的角动量是如何转移出去的.黑洞吸积盘理论提出通过粘滞力矩转移角动量.径移主导吸积盘模型(advection-dominated accretion flow,简称ADAF)是几何厚、光学薄的低吸积率吸积盘模型,它在解释低光度活动星系核的一些观测现象时获得了很大的成功.近年来,随着计算机技术的迅猛发展,数值模拟在天体物理研究中获得了广泛的应用,也取得了突破性的进展.主要工作是用数值模拟方法研究ADAF整体解作为初始条件模拟黑洞的吸积过程. 相似文献
3.
用径移主导吸积流模型（ADAF）不仅可以成功解释很多低吸积率天体的连续谱辐射，也可以说明X射线波段的谱线发射，而后者目前尚少有讨论。以黑洞X射线双星GX339－4处在低吸积率的宁静态情况为例，计算了它的铁线发射，表明在ADAF情况下的确可以产生足够强的可以在观测上检测的类氢和类氦铁Kα线。 相似文献
4.
本文主要研究有热冕存在的吸积盘的特征。首先，我们采用最新的不透明度表和态方程表对经典薄盘的结构进行了探讨。然后考虑吸积盘上下方存在的热冕，分析了冕中的物理过程并研究了冕的结构。在此基础上，我们计算了有冕盘的结构并与无冕盘比较，讨论了盘冕共存系统中物质的蒸发。采用内区径流（亦译为平流）ADAF主导吸积与外区有冕盘吸积方案，研究了黑洞双星系统中光谱态之间转换的作用，提出了黑洞双星系统中光谱态转换的新机制，主要研究成果如下：1、不透明度是吸积盘不稳定性的重要因素。不透明度表和相应的态方程表的改进对吸积盘结构的影响不大，相对于粘滞系数和混合程的不确定性而言是可以忽略的。2、系统的冕结构研究表明，冕的存在对盘的结构有重要影响。吸积物质从冷盘蒸发到热冕中会使内盘物质耗空，在内区只有冕存在。这样的结构将对吸积盘的辐射产生重要作用。3、数值计算了冕的演化，发现物质蒸发使吸积盘理论能自然地诠释如下观测特征：矮新星爆发中出现的紫外边延滞、X－射线后爆发，以及爆发温度。然后，我们提出了新的关于WZ Sge型矮新星和X－射线新星在沉寂阶段的演化模型。在此基础上，我们数值模拟了WZ Sge的长周期演化。4、提出了冕盘的蒸发是吸积从外区薄盘向内区ADAF转化的原因。利用蒸发模型计算了X－射线瞬变源的转换半径，发现理论值与观测值基本一致。5、用有冕盘蒸发模型探讨了X－射线双星中（如Cyg X-1,LMC X-1,LMC X-3)光谱态、从硬到软的变化，发现吸积率的变化导致了ADAF和薄盘之间转换半径的变化，从而使光谱态发生了变化。 相似文献
5.
本文采用了多方物态方程ｐ＝ｋρ＾（１＋１／ｎ）研究了在黑洞附近跨声速α吸积盘的径向线性稳定性，在导出扰动色散关系时考虑了吸积流的径向运动速度，结果表明粘滞系数α存在一上限αｃ，当α＞αｃ时，吸积流是不稳定的，αｃ与多方指数ｎ及吸积流的径向速度ｖｒ有关。 相似文献
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黑洞吸积理论是天体物理学的一个基础理论,是认识许多高能天体系统,如活动星系核、黑洞X射线双星、伽马射线暴等的重要物理基础。该文评述了近年来黑洞吸积理论,尤其是径移主导吸积流(advection-dominated accretion flow,ADAF)模型及其变种的主要发展,并介绍该理论在银河系中心、低光度活动星系核、黑洞X射线双星等方面的应用。全文分为两篇,该文是第一篇,内容是关于黑洞的热吸积流理论及其在银河系中心的应用。 相似文献
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本文在Ｔｈｏｒｎｅ工作的基础上讨论了吸积盘中黑洞的有关参量的演化，以及由Ｓｃｈｗａｒｚｓｃｈｉｌｄ黑洞吸积盘向Ｋｅｒｒ黑洞吸积盘演化过程中对吸积盘辐射通量的影响，最后针对几个典型的辐射过程，分别讨论了黑洞吸积盘在牛顿框架中的温度分布方程与广义相对论的温度分布方程的热不稳定性，并给出此类问题的热不稳定性的判据。 相似文献
10.
本文在Ｔｈｏｒｎｅ工作基础上讨论了吸积盘中黑洞的有关参量的演化，以及由Ｓｃｈｗａ－ｒｚｓｃｈｉｌｄ黑洞吸积盘向Ｋｅｒｒ黑洞吸积盘演化过程中对吸积盘辐射通量的影响，最后针对几个典型的辐射过程，分别讨论了黑洞吸积盘在牛顿框架中的温度分布方程与广义相对论的温度分布方程的热不稳定性，并给出此类问题的热不稳定性的判据。 相似文献
11.
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
12.
《New Astronomy》2007,12(6):471-478
A model of magnetic coupling (MC) of a rotating black hole (BH) with advection-dominated accretion flow (MCADAF) is proposed. It turns out that MCADAF provides a natural explanation for the transition radius between ADAF and SSD, and could be used to interpret the highest luminosity of GX 339-4 in hard-state. A very steep emissivity index can be produced in the innermost part of the MCADAF, which is consistent with the recent XMM-Newton observations of the nearby bright Seyfert 1 galaxy MCG-6-30-15 and with two X-ray binaries (XRBs): XTE J1655-500 and GX 339-4. In addition, we estimate the BH spins in Seyfert 1 galaxy MCG-6-30-15 and in the two XRBs based on this model. 相似文献
13.
3C 84 is a well-known supermassive black hole that can be used to explore jet and accretion physics. In this work, we model the multiwavelength spectral energy distribution (SED) of the 3C 84, and find that the SED is difficult to fit with pure advection dominated accretion flow (ADAF) or pure jet model. Using a coupled ADAF-jet model to fit the SED of 3C 84, it is found that the radio emission and the millimeter emission can be naturally reproduced by the synchrotron radiation of nonthermal electrons in the jet, and that the X-ray emission may predominantly come from inverse Compton radiation from electrons in ADAF. According to the Rotation Measure (RM) obtained by the polarization observation, we consider the possible location of the polarizing source and found that the calculated RM in the jet is roughly consistent with the observational constraints. These results will help us better understand jets produced by black holes. 相似文献
14.
David L. Meier 《Astrophysics and Space Science》2005,300(1-3):55-65
In this paper I propose that the inner part of a black hole accretion inflow (< 100 rg) may enter a magnetically dominated, magnetosphere-like phase in which the strong, well-ordered fields play a more important
role than weak, turbulent fields. In the low/hard state this flow is interior to the standard ADAF usually invoked to explain
the observed hot, optically thin emission. Preliminary solutions for these new MDAFs are presented.
Time-dependent X-ray and radio observations give considerable insight into these processes, and a new interpretation of the
X-ray power spectrum (as arising from many disk radii) may be in order. While an evaporative ADAF model explains the noise
power above 0.01 Hz, an inner MDAF is needed to explain the high-frequency cutoff near 1 Hz, the presence of a QPO, and the
production of a jet. The MDAF scenario also is consistent with the phenomonological models presented at this meeting by several
authors. 相似文献
15.
《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
16.
Ramesh Narayan 《Astrophysics and Space Science》2005,300(1-3):177-188
At luminosities below a few percent of Eddington, accreting black holes switch to a hard spectral state which is very different
from the soft blackbody-like spectral state that is found at higher luminosities. The hard state is well-described by a two-temperature,
optically thin, geometrically thick, advection-dominated accretion flow (ADAF) in which the ions are extremely hot (up to
1012 K near the black hole), the electrons are also hot (∼109−10.5 K), and thermal Comptonization dominates the X-ray emission. The radiative efficiency of an ADAF decreases rapidly with decreasing
mass accretion rate, becoming extremely low when a source reaches quiescence. ADAFs are expected to have strong outflows,
which may explain why relativistic jets are often inferred from the radio emission of these sources. It has been suggested
that most of the X-ray emission also comes from a jet, but this is less well established. 相似文献
17.
观测表明, 黑洞双星的B型准周期振荡(Quasi-Periodic Oscillation, QPO)频率与幂律通量之间存在正相关性. 试图基于阿尔文波振荡模型定量解释该相关性. 标准薄吸积盘辐射通量极大值处的阿尔文波振荡产生QPO. 标准薄盘上的软光子与冕或喷流基部的热电子介质发生逆康普顿散射产生幂律通量. 通过吸积率的连续变化, 得到QPO频率与幂律通量关系的分析解和数值解. 模拟得到的相关性在合理的参数范围内与观测值相吻合. QPO频率与幂律通量的正相关性可以理解为, 较强的磁场导致较高的阿尔文波频率和较高的电子温度从而得到较高的幂律通量. 结果表明B型QPO可能与吸积盘或喷流中的环向磁场的活动有关. 相似文献
18.
R. S. Nemmen R. G. Bower A. Babul T. Storchi-Bergmann 《Monthly notices of the Royal Astronomical Society》2007,377(4):1652-1662
The power of jets from black holes is expected to depend on both the spin of the black hole and the structure of the accretion disc in the region of the last stable orbit. We investigate these dependencies using two different physical models for the jet power: the classical Blandford–Znajek (BZ) model and a hybrid model developed by Meier. In the BZ case, the jets are powered by magnetic fields directly threading the spinning black hole while in the hybrid model, the jet energy is extracted from both the accretion disc as well as the black hole via magnetic fields anchored to the accretion flow inside and outside the hole's ergosphere. The hybrid model takes advantage of the strengths of both the Blandford–Payne and BZ mechanisms, while avoiding the more controversial features of the latter. We develop these models more fully to account for general relativistic effects and to focus on advection-dominated accretion flows (ADAFs) for which the jet power is expected to be a significant fraction of the accreted rest mass energy.
We apply the models to elliptical galaxies, in order to see if these models can explain the observed correlation between the Bondi accretion rates and the total jet powers. For typical values of the disc viscosity parameter α∼ 0.04 –0.3 and mass accretion rates consistent with ADAF model expectations, we find that the observed correlation requires j ≳ 0.9 ; that is, it implies that the black holes are rapidly spinning. Our results suggest that the central black holes in the cores of clusters of galaxies must be rapidly rotating in order to drive jets powerful enough to heat the intracluster medium and quench cooling flows. 相似文献
We apply the models to elliptical galaxies, in order to see if these models can explain the observed correlation between the Bondi accretion rates and the total jet powers. For typical values of the disc viscosity parameter α∼ 0.04 –0.3 and mass accretion rates consistent with ADAF model expectations, we find that the observed correlation requires j ≳ 0.9 ; that is, it implies that the black holes are rapidly spinning. Our results suggest that the central black holes in the cores of clusters of galaxies must be rapidly rotating in order to drive jets powerful enough to heat the intracluster medium and quench cooling flows. 相似文献