星系中心大黑洞的宇宙学演化

在冷暗物质晕等级成团宇宙学模型中,伴随着暗物质晕并合,星系中心黑洞也断地并合和增长.于展Press-Schechter公式（EPS）我们编写了一自适应时间长Monte Carlo程序,重构了表征暗物质晕等级成团并合树.在成功地建立了黑洞和暗物质晕宇宙学演化模型后,我们通过引入直接吸积（包标准薄盘吸积和磁流体力学吸积）和随吸积两类黑洞吸积模式,论了黑洞自旋和质量宇宙学演化.通过与观测到AGN光度函数比较,我们发现黑洞通过磁流体力学吸积模式增长,与观测符合最好.于以上理论框架,我们还研究了双大质量黑洞演化,发现双黑洞通过共转气体吸积盘吸积对双黑洞质量比分存在显著影响.     

The magnetic nature of disk accretion onto black holes

Although disk accretion onto compact objects-white dwarfs, neutron stars and black holes-is central to much of high-energy astrophysics, the mechanisms that enable this process have remained observationally difficult to determine. Accretion disks must transfer angular momentum in order for matter to travel radially inward onto the compact object. Internal viscosity from magnetic processes and disk winds can both in principle transfer angular momentum, but hitherto we lacked evidence that either occurs. Here we report that an X-ray-absorbing wind discovered in an observation of the stellar-mass black hole binary GRO J1655 - 40 (ref. 6) must be powered by a magnetic process that can also drive accretion through the disk. Detailed spectral analysis and modelling of the wind shows that it can only be powered by pressure generated by magnetic viscosity internal to the disk or magnetocentrifugal forces. This result demonstrates that disk accretion onto black holes is a fundamentally magnetic process.     

Observational evidence for the accretion-disk origin for a radio jet in an active galaxy

Accretion of gas onto black holes is thought to power the relativistic jets of material ejected from active galactic nuclei (AGN) and the 'microquasars' located in our Galaxy. In microquasars, superluminal radio-emitting features appear and propagate along the jet shortly after sudden decreases in the X-ray fluxes. This establishes a direct observational link between the black hole and the jet: the X-ray dip is probably caused by the disappearance of a section of the inner accretion disk as it falls past the event horizon, while the remainder of the disk section is ejected into the jet, creating the appearance of a superluminal bright spot. No such connection has hitherto been established for AGN, because of insufficient multi-frequency data. Here we report the results of three years of monitoring the X-ray and radio emission of the galaxy 3C120. As has been observed for microquasars, we find that dips in the X-ray emission are followed by ejections of bright superluminal knots in the radio jet. The mean time between X-ray dips appears to scale roughly with the mass of the black hole, although there are at present only a few data points.     

An ultra-relativistic outflow from a neutron star accreting gas from a companion

Collimated relativistic outflows-also known as jets-are amongst the most energetic phenomena in the Universe. They are associated with supermassive black holes in distant active galactic nuclei, accreting stellar-mass black holes and neutron stars in binary systems and are believed to be responsible for gamma-ray bursts. The physics of these jets, however, remains something of a mystery in that their bulk velocities, compositions and energetics remain poorly determined. Here we report the discovery of an ultra-relativistic outflow from a neutron star accreting gas within a binary stellar system. The velocity of the outflow is comparable to the fastest-moving flows observed from active galactic nuclei, and its strength is modulated by the rate of accretion of material onto the neutron star. Shocks are energized further downstream in the flow, which are themselves moving at mildly relativistic bulk velocities and are the sites of the observed synchrotron emission from the jet. We conclude that the generation of highly relativistic outflows does not require properties that are unique to black holes, such as an event horizon.     

The discovery of a galaxy-wide superwind from a young massive galaxy at redshift z approximately 3

High-velocity galactic outflows, driven by intense bursts of star formation and black hole accretion, are processes invoked by current theories of galaxy formation to terminate star formation in the most massive galaxies and to deposit heavy elements in the intergalactic medium. From existing observational evidence (for high-redshift galaxies) it is unclear whether such outflows are localized to regions of intense star formation just a few kiloparsecs in extent, or whether they instead have a significant impact on the entire galaxy and its surroundings. Here we present two-dimensional spectroscopy of a star-forming galaxy at redshift z = 3.09 (seen 11.5 gigayears ago, when the Universe was 20 per cent of its current age): its spatially extended Lyalpha line emission appears to be absorbed by H i in a foreground screen covering the entire galaxy, with a lateral extent of at least 100 kpc and remarkable velocity coherence. This screen was ejected from the galaxy during a starburst several 10(8) years earlier and has subsequently swept up gas from the surrounding intergalactic medium and cooled. This demonstrates the galaxy-wide impact of high-redshift superwinds.     

A periodicity of approximately 1 hour in X-ray emission from the active galaxy RE J1034+396

Active galactic nuclei and quasars are thought to be scaled-up versions of Galactic black hole binaries, powered by accretion onto supermassive black holes with masses of 10(6)-10(9) M[symbol: see text], as opposed to the approximately 10 M [symbol: see text] in binaries (here M [symbol: see text] is the solar mass). One example of the similarities between these two types of systems is the characteristic rapid X-ray variability seen from the accretion flow. The power spectrum of this variability in black hole binaries consists of a broad noise with multiple quasi-periodic oscillations superimposed on it. Although the broad noise component has been observed in many active galactic nuclei, there have hitherto been no significant detections of quasi-periodic oscillations. Here we report the discovery of an approximately 1-hour X-ray periodicity in a bright active galaxy, RE J1034+396. The signal is highly statistically significant (at the 5.6 sigma level) and very coherent, with quality factor Q > 16. The X-ray modulation arises from the direct vicinity of the black hole.     

活动星系核中黑洞质量与宇宙学红移的研究

收集了209个活动星系核（46个平谱射电类星体,78个BLLac天体,85个射电星系）样本,估算出爱丁顿吸积率,讨论了黑洞质量、热光度、红移量和爱丁顿吸积率之间的关系,得出了以下结论：（1）活动星系核的一个演化序列为：平谱射电类星体（FsRQ）——BL Lac天体——射电星系（RG）的演化;（2）三类星体的中心黑洞质量、红移量和热光度有较大差异：皆为FSRQ〉BLLac〉RG;（3）吸积率与热光度之间的相关性很强,吸积率的变化将导致热光度的变化。     

A close nuclear black-hole pair in the spiral galaxy NGC 3393

The current picture of galaxy evolution advocates co-evolution of galaxies and their nuclear massive black holes, through accretion and galactic merging. Pairs of quasars, each with a massive black hole at the centre of its galaxy, have separations of 6,000 to 300,000 light years (refs 2 and 3; 1 parsec = 3.26 light years) and exemplify the first stages of this gravitational interaction. The final stages of the black-hole merging process, through binary black holes and final collapse into a single black hole with gravitational wave emission, are consistent with the sub-light-year separation inferred from the optical spectra and light-variability of two such quasars. The double active nuclei of a few nearby galaxies with disrupted morphology and intense star formation (such as NGC 6240 with a separation of about 2,600 light years and Mrk 463 with a separation of about 13,000 light years between the nuclei) demonstrate the importance of major mergers of equal-mass spiral galaxies in this evolution; such mergers lead to an elliptical galaxy, as in the case of the double-radio-nucleus elliptical galaxy 0402+379 (with a separation of about 24 light years between the nuclei). Minor mergers of a spiral galaxy with a smaller companion should be a more common occurrence, evolving into spiral galaxies with active massive black-hole pairs, but have hitherto not been seen. Here we report the presence of two active massive black holes, separated by about 490 light years, in the Seyfert galaxy NGC 3393 (50 Mpc, about 160 million light years). The regular spiral morphology and predominantly old circum-nuclear stellar population of this galaxy, and the closeness of the black holes embedded in the bulge, provide a hitherto missing observational point to the study of galaxy/black hole evolution. Comparison of our observations with current theoretical models of mergers suggests that they are the result of minor merger evolution.     

Active galactic nuclei as scaled-up Galactic black holes

A long-standing question is whether active galactic nuclei (AGN) vary like Galactic black hole systems when appropriately scaled up by mass. If so, we can then determine how AGN should behave on cosmological timescales by studying the brighter and much faster varying Galactic systems. As X-ray emission is produced very close to the black holes, it provides one of the best diagnostics of their behaviour. A characteristic timescale--which potentially could tell us about the mass of the black hole--is found in the X-ray variations from both AGN and Galactic black holes, but whether it is physically meaningful to compare the two has been questioned. Here we report that, after correcting for variations in the accretion rate, the timescales can be physically linked, revealing that the accretion process is exactly the same for small and large black holes. Strong support for this linkage comes, perhaps surprisingly, from the permitted optical emission lines in AGN whose widths (in both broad-line AGN and narrow-emission-line Seyfert 1 galaxies) correlate strongly with the characteristic X-ray timescale, exactly as expected from the AGN black hole masses and accretion rates. So AGN really are just scaled-up Galactic black holes.     

Birth of a relativistic outflow in the unusual γ-ray transient Swift J164449.3+573451

Active galactic nuclei, which are powered by long-term accretion onto central supermassive black holes, produce relativistic jets with lifetimes of at least one million years, and the observation of the birth of such a jet is therefore unlikely. Transient accretion onto a supermassive black hole, for example through the tidal disruption of a stray star, thus offers a rare opportunity to study the birth of a relativistic jet. On 25 March 2011, an unusual transient source (Swift J164449.3+573451) was found, potentially representing such an accretion event. Here we report observations spanning centimetre to millimetre wavelengths and covering the first month of evolution of a luminous radio transient associated with Swift J164449.3+573451. The radio transient coincides with the nucleus of an inactive galaxy. We conclude that we are seeing a newly formed relativistic outflow, launched by transient accretion onto a million-solar-mass black hole. A relativistic outflow is not predicted in this situation, but we show that the tidal disruption of a star naturally explains the observed high-energy properties and radio luminosity and the inferred rate of such events. The weaker beaming in the radio-frequency spectrum relative to γ-rays or X-rays suggests that radio searches may uncover similar events out to redshifts of z?≈?6.     

活动星系核中心黑洞的质量与进动

为了考察活动星系核中心黑洞质量对其进动的影响,本文对活动星系核中吸积盘驱使黑洞及其喷流进动的模型即盘致进动模型作了进一步研究.首先,在进动周期-绝对星等关系中代入由观测得到的黑洞质量,结果弥散度有所减小;其次,对此模型中黑洞质量与其进动锥角在演化过程中应有的关系做了理论分析并绘出理论曲线,发现它们之间是反相关的;最后,详细考察黑洞质量和进动锥角观测值的实际分布,发现理论曲线与实际数据是相吻合的.所以,盘致进动模型对黑洞进动现象的解释是比较合理的.     

The suppression of star formation by powerful active galactic nuclei

The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.     

Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre

The cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation. Sagittarius A* (Sgr A*), the compact source of radio, infrared and X-ray emission at the centre of the Milky Way, is the closest example of this phenomenon, with an estimated black hole mass that is 4,000,000 times that of the Sun. A long-standing astronomical goal is to resolve structures in the innermost accretion flow surrounding Sgr A*, where strong gravitational fields will distort the appearance of radiation emitted near the black hole. Radio observations at wavelengths of 3.5 mm and 7 mm have detected intrinsic structure in Sgr A*, but the spatial resolution of observations at these wavelengths is limited by interstellar scattering. Here we report observations at a wavelength of 1.3 mm that set a size of 37(+16)(-10) microarcseconds on the intrinsic diameter of Sgr A*. This is less than the expected apparent size of the event horizon of the presumed black hole, suggesting that the bulk of Sgr A* emission may not be centred on the black hole, but arises in the surrounding accretion flow.     

The essential signature of a massive starburst in a distant quasar

Observations of carbon monoxide emission in high-redshift (zeta > 2) galaxies indicate the presence of large amounts of molecular gas. Many of these galaxies contain an active galactic nucleus powered by accretion of gas onto a supermassive black hole, and a key question is whether their extremely high infrared luminosities result from the active galactic nucleus, from bursts of massive star formation (associated with the molecular gas), or both. In the Milky Way, high-mass stars form in the dense cores of interstellar molecular clouds, where gas densities are n(H2) > 10(5) cm(-3) (refs 1, 2). Recent surveys show that virtually all galactic sites of high-mass star formation have similarly high densities. The bulk of the cloud material traced by CO observations, however, is at a much lower density. For galaxies in the local Universe, the HCN molecule is an effective tracer of high-density molecular gas. Here we report observations of HCN emission from the infrared-luminous 'Cloverleaf' quasar (at a redshift zeta = 2.5579). The HCN line luminosity indicates the presence of 10 billion solar masses of very dense gas, an essential feature of an immense starburst, which contributes, together with the active galactic nucleus it harbours, to its high infrared luminosity.     

MCG-6-30-15的铁Ka线的研究

活动星系核的X射线性质是近几十年X射线天文学研究的一大热点。铁Ka线位于X波段的6-7keY能区,是来自活动星系核中的冷物质的荧光辐射。随着XMM-Newton和Chandra等高性能X射线望远镜投入使用,铁Ka线的研究也更加深入。通常,宽的铁Ka线被认为是研究AGN中心黑洞最好的探针,一个最著名的例子就是MCG-6-30-15。ASCA和XMM-Newton卫星已经对MCG-6-30-15进行了多次观测和研究,发现有明显的宽的铁Ka线存在。研究铁Kn线的轮廓能给出黑洞自旋的一些信息,这些信息对了解黑洞的吸积、演化有重要意义。文章选取XMM-Newton卫星已对MC@6-30-15的一次观测来研究MC@6-30-15铁Ka线性质。     

核心坍缩超新星中心黑洞超吸积在星系尺度上的贡献

核心坍缩超新星(Core-Collapse Supernova,CCSN)是大质量恒星演化末期的爆发现象,产生了宇宙中大多数的中子星和恒星级黑洞等致密天体.爆发可能伴随着强磁场中子星或黑洞超吸积引发的剧烈长时标伽马射线暴.CCSN还被认为是宇宙重元素的主要来源之一.本综述介绍了我们近期对CCSN中心黑洞超吸积过程的系列研究成果,主要包括研究了大质量星系中心附近伽马射线暴余辉阶段,因大量暗物质粒子湮灭电子注入而引发的光变和能谱的形态变化,探讨了其作为暗物质探测手段的可能性;研究了坍缩星框架下,中微子主导吸积流外流对核合成的贡献,及对太阳临近空间、(活动)星系等化学组分和演化的影响;最后,从数值模拟角度讨论了CCSN起源的致密天体质量分布,给出了低质量间隙可能起源于CCSN爆发能量分布的结论.     

A collimated, high-speed outflow from the dying star V Hydrae

Stars with masses in the range 1-8 solar masses (M(\circ)) live ordinary lives for approximately 10(9)-10(10) years, but die extraordinary deaths. First, during their death throes as asymptotic giant branch (AGB) stars they eject, over 10(4)-10(5) years, half or more of their mass in slowly expanding, spherical winds, and then, in a short (a few 100-1,000 years) and poorly understood phase, they are transformed into aspherical planetary nebula. Recent studies support the idea that high-speed, jet-like flows play a crucial role in this transformation. Evidence for such outflows is indirect, however; this phase is so short that few nearby stars are likely to be caught in the act. Here we report the discovery of a newly launched, high-speed jet-like outflow in the nearby AGB star, V Hydrae. We have detected both proper motions and ongoing evolution in the jet. These results support a model in which the jet is driven by an accretion disk around an unseen, compact companion. We also find a central, dense equatorial disk-like structure which may enable and/or enhance the formation of the accretion disk.     

活动星系核吸积盘辐射的研究

在标准吸积盘辐射模型的基础上,考虑了不同的质量吸积率、不同的无量纲旋转参数a(中心黑洞为克尔黑洞)、最小稳定轨道半径处存在的约束(产生一个矩)和吸积盘表面磁场的存在(喷流辐射与吸积盘辐射之间存在一定的耦合)对吸积盘辐射的影响。结果表明,中心黑洞为正旋转的克尔黑洞比史瓦西黑洞辐射的峰值及峰值频率大,负旋转的克尔黑洞比史瓦西黑洞辐射的峰值及峰值频率小,质量吸积率越大峰值和峰值频率变大,无量纲黑洞旋转参数a越大峰值与峰值频率越大,喷流辐射能量和吸积盘辐射能量之比越大峰值和峰值频率越小,辐射效率越大峰值和峰值频率越大。     

On thermodynamical evolution of Kerr black holes in active galactic nuclei

The effect of Blandford-Znajek process on the thermodynamical evolution of Kerr black holes in active galactic nuclei is discussed. It is demonstrated that a black hole does not evolve into an extreme Kerr state provided anti-accretion process exists.     

吸积盘中心黑洞的熵变与 B-Z 过程

分别在薄盘和厚盘两种情况下,详细讨论了纯吸积过程和Ｂ－Ｚ过程中吸积盘中心黑洞的熵变．结果表明,中心黑洞各参量在Ｂ－Ｚ过程中的变化率与在纯吸积过程中的变化率之差与盘结构无关,而且与Ｂ－Ｚ过程的辐射功率成正比．在Ｂ－Ｚ过程中黑洞熵的变化率总是大于纯吸积过程中黑洞熵的变化率,二者之差来自中心黑洞延伸视界上的耗散功率．此外,还讨论了黑洞热力学定律在上述盘吸积过程中的有效性．