Theoretical Study of Radio Galaxies

我们对射电星系中相对论喷流的物理性质和体加速机制进行了理论研究.在双流体和一维近似下，我们求解了正负电子对从热吸积盘中流出的问题。我们发现，当吸积速率较高时，盘中耗散能量的大部分转化为对的内能和动能，这证实了我们以前基于单区近似的结果.这是第一个成功地将引力能释放与喷流形成联系起来的机制.在体加速机制方面，我们研究了相对论温度下与光子处于维恩平衡的电子-正电子对的热加速。我们解决了稳定和球对称流出，并发现终端洛伦兹因子很容易达到几十个相当大的效率。这种机制自然地避免了以前的对湮灭和辐射阻力的困难，因此被证明是非常有前途的。准直问题仍有待解决。这一机制预测了伴随喷流形成的强MeV伽马射线辐射，这可以通过未来的观测来检验。虽然相对论喷流的相当一部分能量在中央发动机附近的内部激波中辐射，但其余部分被转换为扩展射电源的动能和内部能量。我们已经检查了物理量，如磁场和相对论电子在热点和叶，发现它们是兼容的喷流模型主要由电子-正电子对。

We have made theoretical investigations on the physical properties and bulk acceleration mechanism of relativistic jets in radio galaxies.1. We have solved the outflow of electron-positron pairs from hot accretion disks under the two-fluid and one-dimensional approximations. We have found that a major portion of the dissipated energy in the disk is converted to the internal and kinetic energies of pairs when the accretion rate is high, which confirms our previous result based on the one-zone approximation. This specific mechanism is the first successful one which connects gravitational energy release with jet formation.2. As for the bulk acceleration mechanism, we have investigated thermal acceleration of electron-positron pairs in a Wien equilibrium with photons at a relativistic temperature. We solved steady and spherically symmetric outflows and found that the terminal Lorentz factor easily reaches a few tens with a quite large efficiency. This mechanism is shown to naturally avoid previous difficulties of pair annihilation and radiation drag and thus proves to be very promising. The collimation problem remains to be open. This mechanism predicts strong MeV gamma-ray emission accompanying the jet formation, which can be checked by future observations.3. While a fair fraction of the energy of the relativistic jets is radiated in the internal shocks near the central engine, the remaining fraction is converted to the kinetic and internal energies of extended radio sources. We have examined the physical quantities such as magnetic field and relativistic electrons in the hot spots and lobes and found that they are compatible with our jet model consisting of mainly electron-positron pairs.