黑洞吸积盘中磁场的放大及黑洞双星的谱态转变

详细讨论了吸积盘中的磁场放大过程-dynamo(发电机)机制,并利用dynamo机制拟合黑洞双星谱态转变的时标.在磁场没有被放大之前,经典薄盘对应的谱态是热态,当大尺度磁场形成之后,经典薄盘演化为磁化吸积盘,其对应的谱态演化为陡幂律(SPL)态.     

标准薄盘径移速度对谱线轮廓影响研究

 在考虑标准薄盘流体元径移速度的情况下,推导出Kerr黑洞附近吸积盘的观测谱线流量的一般计算式.利用光子追踪法,计算不同参数条件下薄吸积盘的谱线轮廓,通过比较考虑径移速度vr和忽略径移速度vr=0两种情况下吸积盘的谱线轮廓,得出在多数情况下,径移速度对谱线流量的影响是不可忽略的.     

径移速度对SSD谱线轮廓及成像影响

在考虑标准薄盘流体元径移速度的情况下,推导出Kerr黑洞附近吸积盘的观测谱线流量的一般计算式．利用光子追踪法,计算不同参数条件下标准薄吸积盘的谱线轮廓,通过比较考虑径移速度和忽略径移速度两种情况下吸积盘的谱线轮廓,得出在多数情况下,径移速度对谱线流量的影响是显著的,两种情况下吸积盘流量成像图形状基本不变．     

黑洞吸积盘径向参量的演化

利用黑洞吸积盘演化的基本方程组 ,在纯吸积情况下 ,求得了薄、厚吸积盘及一般厚吸积盘的黑洞视界半径rH的演化方程 .证实了中心黑洞与吸积盘相互影响的基本性质 ,并得到一些新的结果 .黑洞视界半径rH演化并非完全单调 ,其演化特性与吸积盘的类型有关 :对于薄盘 ,rH单调递增 ;对于临界厚盘 ,rH先增后减 ;对于一般厚盘 ,rH先增后减再递增 .还讨论了吸积盘内边缘与黑洞视界间隔的演化 .     

有限厚度吸积盘对标准薄盘静态结构和稳定性的影响

对标准薄盘模型,当吸积率M大于某临界值M_B时吸积盘的静态平衡结构将是不稳定的,同时原来的薄盘近似h≡H/R(?)1也不再成立。采用微扰论的方法研究了当h(?)1不成立但仍有h<1时的有限厚度对吸积盘静态结构及其稳定性的影响。结果表明,它使平衡曲线除原有的稳定分支和不稳定分支外,将增加1条新的稳定分支,即M(∑)平衡曲线具有“S”形特征,因而存在极限环演化行为。     

原恒星的准Keplerian吸积盘模型

本文从有限电导率的 MHD 方程出发,考虑气体压强梯度对转动的影响,在薄盘稳定和轴对称的假设下导出了原恒星吸积盘的一组自洽解析解,得出温度与半径关系 T=T_0R~(-3/4) 。     

弱磁化等温吸积盘脉动不稳定性

在不引入粘滞律的条件下详细讨论了弱磁化等温吸积盘对各种扰动形式所表现的不稳定性．结果表明,径向扰动能与环向扰动和垂向扰动相耦合,产生不同类型的脉动不稳定振荡模式．这些结果不仅对进一步理解脉动不稳定性与活动天体的光变现象的联系有理论意义,而且在某种程度上对Ｂａｌｂｕｓ和Ｈａｗｌｅｙ等人提出的弱磁场与吸积盘中湍流粘滞有关联的解释是一种支持与补充．     

磁场对中微子主导吸积盘粒子丰度的影响

中微子主导吸积盘被认为可能是伽玛射线暴中心能源机制的一种模型.为了详细地考虑微观粒子分布,计算了伪牛顿势框架下磁场对中微子主导吸积盘微观粒子丰度的影响.结果表明,在吸积盘的外区,磁场对粒子丰度和电子简并度几乎没有影响；而在吸积盘的内区,考虑和没考虑磁场时,电子简并度,电子、中子等粒子丰度具有比较大的差异.     

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．     

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。     

自引力均分吸积盘的不稳定性

采用微扰方法导了磁粘滞情况下自引力均分薄吸积盘的色散方程研究了吸积秀斩不稳定性，并分析了自引力，磁场，粘滞对吸积盘不稳定性的影响，数值计算表明，在同时考虑自引力和磁场时，吸积盘存在着３种振荡模式（总是稳定的粘滞横模式和通常不稳定的磁声模式及中性模式）这些结果为解释ＢＬ．Ｌａｃ天体，Ｓｅｙｆｅｒｔ星系，类星体等活动星系核的光变现象提供了理论依据。     

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.     

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。     

Direct detection of a magnetic field in the innermost regions of an accretion disk

Models predict that magnetic fields play a crucial role in the physics of astrophysical accretion disks and their associated winds and jets. For example, the rotation of the disk twists around the rotation axis the initially vertical magnetic field, which responds by slowing down the plasma in the disk and by causing it to fall towards the central star. The magnetic energy flux produced in this process points away from the disk, pushing the surface plasma outwards, leading to a wind from the disk and sometimes a collimated jet. But these predictions have hitherto not been supported by observations. Here we report the direct detection of the magnetic field in the core of the protostellar accretion disk FU Orionis. The surface field reaches strengths of about 1 kG close to the centre of the disk, and it includes a significant azimuthal component, in good agreement with recent models. But we find that the field is very filamentary and slows down the disk plasma much more than models predict, which may explain why FU Ori fails to collimate its wind into a jet.     

Circular polarimetry reveals helical magnetic fields in the young stellar object HH 135-136

Magnetic fields are believed to have a vital role in regulating and shaping the flow of material onto and away from protostars during their initial mass accretion phase. It is becoming increasingly accepted that bipolar outflows are generated and collimated as material is driven along magnetic field lines and centrifugally accelerated off a rotating accretion disk. However, the precise role of the magnetic field is poorly understood and evidence for its shape and structure has not been forthcoming. Here we report imaging circular polarimetry in the near-infrared and Monte Carlo modelling showing that the magnetic field along the bipolar outflow of the HH 135-136 young stellar object is helical. The field retains this shape for large distances along the outflow, so the field structure can also provide the necessary magnetic pressure for collimation of the outflow. This result lends further weight to the hypothesis--central to any theory of star formation--that the outflow is an important instrument for the removal of high-angular-momentum material from the accretion disk, thereby allowing the central protostar to increase its mass.     

磁场从黑洞吸积盘提取能量的解析模型

提出了一种磁场提取黑洞吸积盘能量的解析模型,其中涉及到3种能量机制: (1) Blandford-Znajek (BZ)与连接黑洞与天体物理负载的开放磁力线有关, (2) 磁耦合(MC)过程与连接黑洞与盘负载的闭合磁力线有关, (3) DL过程与连接吸积盘与天体物理负载的开放磁力线有关.利用等效电路导出上述能量机制的电磁功率和力矩表达式.此外还讨论了这个模型潜在的天体物理应用.     

反常粘滞吸积薄盘的稳定结构

根据描述吸积盘的流体动力学方程,给出无磁场情况下的质量、动量和能量守恒方程。在所给定方程的基础上,利用新的反常粘滞计算了黑洞周围吸积盘内区的结构。数值结果表明盘内区的气体不是做开普勒旋转,温度随吸积率变化比较明显,在M=10M_⊙,M ^.=100M ^._E的情况下,吸积盘的最大温度可达到3.35×10⁷K。 同时文中也给出了面密度和径向速度的分布规律。     

MHD吸积盘上两种能量转移机制的比较

MHD张力在黑洞吸积盘模型的角动量转移上扮演重要的角色，大尺度上的MHD力矩促进吸积盘垂直向的角动量转移，并出现与吸积相关的各种流的普遍现象，而且能够影响吸积盘的辐射谱。在标准吸积盘辐射模型的基础上，考虑坡印廷流主导（Poynting-fluxdominated）和物质流主导（Mass—fluxdominated）（质量吸积率随吸积盘的半径而变化），对吸积盘辐射产生的变化。理论表明两种主导因素对标准吸积盘的辐射能够产生很好的修正。同时两种主导模型之间也存在着一定的差别。坡印廷流主导的盘产生的辐射峰值频率比物质流主导的要高。物质流主导的吸积盘产生的辐射谱型在低频部分要比坡印廷流主导的要平坦。     

An optical counterpart to the anomalous X-ray pulsar 4U0142+61

The energy source of the anomalous X-ray pulsars (AXPs) is not understood, hence their designation as anomalous. Unlike binary X-ray pulsars, no companions are seen, so the energy cannot be supplied by accretion of matter from a companion star. The loss of rotational energy, which powers radio pulsars, is insufficient to power AXPs. Two models are generally considered: accretion from a large disk left over from the birth process, or decay of a very strong magnetic field (10(15) G) associated with a 'magnetar'. The lack of counterparts at other wavelengths has hampered progress in our understanding of these objects. Here we report deep optical observations of the field around 4U0142+61, which is the brightest AXP in X-rays. The source has no associated supernova remnant, which, together with its spin-down timescale of approximately 10(5) yr (ref. 5), suggests that it may be relatively old. We find an object with peculiar optical colours at the position of the X-ray source, and argue that it is the optical counterpart. The optical emission is too faint to admit the presence of a large accretion disk, but may be consistent with magnetospheric emission from a magnetar.