动力摩擦的自洽的、随时间变化的处理：关于堆芯失速和动力浮力的新认识
A Self-Consistent, Time-Dependent Treatment of Dynamical Friction: New Insights regarding Core Stalling and Dynamical Buoyancy
摘要：
动力学摩擦通常被认为是一个长期的过程，其中主体（“扰动者”）发展得非常缓慢（长期近似），并且已经在很长一段时间内被引入主体（绝热近似）。这些假设意味着动力学摩擦产生的LBK扭矩的非零贡献，只有从纯共振轨道。然而，动力学摩擦只有在其时间尺度小于宇宙年龄时才具有天体物理学意义。因此，在本文中，我们放松绝热和长期的近似。我们首先推导出一个广义的LBK扭矩，这减少了在绝热极限的LBK扭矩，并表明，它会引起瞬态振荡，由于非共振轨道，慢慢衰减，让位于LBK扭矩。这类似于受迫阻尼振荡器在稳定到稳态之前如何经历瞬态，除了这里的阻尼是由于相位混合而不是耗散。接下来，我们提出了一个自洽的治疗，适当占时间依赖性的扰动势和循环频率（记忆效应），我们用它来检查在核心星系的轨道衰变。我们发现，记忆效应的结果，在一个阶段的加速，超brasekhar摩擦前的扰动失速在一个临界半径，$R_{\mathrm{crit}}$，在核心（核心失速）。在$R_{\mathrm{crit}}$内部，扭矩翻转符号，产生动态浮力，动态浮力抵消摩擦并导致扰动器失速。这种现象与$N$ -体模拟一致，但迄今为止还没有得到适当的解释。
英文摘要：
Dynamical friction is typically regarded a secular process, in which the subject ('perturber') evolves very slowly (secular approximation), and has been introduced to the host over a long time (adiabatic approximation). These assumptions imply that dynamical friction arises from the LBK torque with non-zero contribution only from pure resonance orbits. However, dynamical friction is only of astrophysical interest if its timescale is shorter than the age of the Universe. In this paper we therefore relax the adiabatic and secular approximations. We first derive a generalized LBK torque, which reduces to the LBK torque in the adiabatic limit, and show that it gives rise to transient oscillations due to non-resonant orbits that slowly damp out, giving way to the LBK torque. This is analogous to how a forced, damped oscillator undergoes transients before settling to a steady state, except that here the damping is due to phase mixing rather than dissipation. Next, we present a self-consistent treatment, that properly accounts for time-dependence of the perturber potential and circular frequency (memory effect), which we use to examine orbital decay in a cored galaxy. We find that the memory effect results in a phase of accelerated, super-Chandrasekhar friction before the perturber stalls at a critical radius, $R_{\mathrm{crit}}$, in the core (core-stalling). Inside of $R_{\mathrm{crit}}$ the torque flips sign, giving rise to dynamical buoyancy, which counteracts friction and causes the perturber to stall. This phenomenology is consistent with $N$-body simulations, but has thus far eluded proper explanation.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
