Dynamics of Massive Fields in Black Hole Spacetimes

人们从不同的角度研究了强引力引起的黑洞的有趣性质。特别是微扰场的动力学演化一直是黑洞物理学的基本问题之一。本研究的主要目的是发现黑洞周围标量场由于静止质量不为零而引起的演化行为的新方面。1.首先，研究了有质量标量场的晚时尾。如果电磁场辐射到远处，电磁场的振幅会随着时间的推移而衰减。研究发现，辐射的共振反向散射对后期演化起着重要作用，并且在所有球对称黑洞时空中，普适幂律衰变成为主导行为。这一依赖于解析绿色函数技术的结果得到了其他研究小组数值计算的验证。与无质量场的标准衰减律相比，有质量场的幂律衰减要慢得多，这将有助于从观测上检验场是无质量的还是有质量的。2.其次，考虑旋转黑洞周围均匀磁场的影响，研究了Kerr背景几何中带电（有质量）标量场的束缚态。场的超辐射放大被发现，有趣的是，它的增长率是至关重要的依赖于场电荷的符号。这可能是在黑洞磁层中产生大量净电荷并引发电磁爆发现象的一种机制。

The interesting properties of black holes due to strong gravity have been studied from various viewpoints. In particular, the dynamical evolution of perturbative fields has been one of the fundamental problems in black hole physics. The main purpose of this research project is to find new aspects of the evolutionary behaviors due to the non-zero rest mass of scalar fields around a black hole.1.First, the late-time tails of massive scalar fields are studied. The field amplitude should decay with the lapse of time, if the fields are radiated away to a distant region. It is found that a resonant backscattering of the radiation can play an important role for the late-time evolution, and in all spherically symmetric black hole spacetimes a universal power-law decay becomes the dominant behavior. This result relied on the analytical Green function technique is verified by numerical calculations done by other research groups. The power-law decay of massive fields is quite slower if compared with the standard decay law established for massless fields and will be useful to check observationally whether the fields are massless or massive.2.Next, the bound states of charged (massive) scalar fields in Kerr background geometry are investigated, by considering the effect of a uniform magnetic field around the rotating black hole. The superradiant amplification of the fields is found, and interestingly it is shown that the growing rate is crucially dependent on the sign of the field charge. This can be a mechanism to generate a large net charge in the black hole magnetosphere and to trigger electromagnetic burst phenomena.