Causality and stability of cosmic jets
Causality and stability of cosmic jets
复制标题
宇宙喷流的因果关系和稳定性
DOI：
10.1093/mnras/stv1295
复制
发表时间：
2014
影响因子：
4.8
通讯作者：
S. Komissarov
中科院分区：
文献类型：
--
作者：
O. Porth;O. Porth;S. Komissarov;S. Komissarov
与实验室和地球上的对应物形成鲜明对比的是，宇宙喷流似乎非常稳定。它们能够穿透广阔的空间，这些空间的大小超过其中央发动机的十亿倍。我们提出，这一显着的属性背后的原因是这些喷气机之间的因果连接的损失，造成他们的快速扩张，以响应快速下降的外部压力与距离的“喷气发动机”。在具有幂律压力分布的大气中，pext / z，当> 2 {陡度，这在许多天体物理环境中是很常见的，因果连通性就会完全丧失。这个结论似乎并不依赖于喷流的物理性质-它适用于相对论和非相对论流，包括磁主导和非磁化喷流。为了验证这一点，我们已经进行了中等磁化和中等相对论射流的数值模拟。研究结果有力地支持了我们的假设，并提供了有价值的见解。特别是，我们发现，z箍缩的磁射流的内核扩展速度比他们的信封，变得容易受到不稳定性，即使当整个射流是稳定的。这可能会导致局部耗散和排放，而不会导致流动的整体分解。当宇宙喷流进入外部大气层时，它们可能会变得全球不稳定。我们建议，Fanaro-Riley形态划分河外射电源分为两类是与这个问题。特别是，我们认为，低功率FR-I喷气机成为重新限制，因果关系连接和全球不稳定的银河X射线日冕的规模，而更强大的FR-II喷气机重新限制更远，已经在射电瓣的规模，并保持基本完整，直到他们终止在热点。利用这一思想，我们导出了临界喷流功率与宿主星系光学光度之间的关系，与观测结果符合得很好。
In stark contrast to their laboratory and terrestrial counterparts, cosmic jets appear to be very stable. They are able to penetrate vast spaces, which exceed by up to a billion times the size of their central engines. We propose that the reason behind this remarkable property is the loss of causal connectivity across these jets, caused by their rapid expansion in response to fast decline of external pressure with the distance from the "jet engine". In atmospheres with power-law pressure distribution, pext / z , the total loss of causal connectivity occurs, when > 2 { the steepness which is expected to be quite common for many astrophysical environments. This conclusion does not seem to depend on the physical nature of jets- it applies both to relativistic and non-relativistic flows, both magnetically-dominated and unmagnetised jets. In order to verify it, we have carried out numerical simulations of moderately magnetised and moderately relativistic jets. The results give strong support to our hypothesis and provide with valuable insights. In particular, we find that the z-pinched inner cores of magnetic jets expand slower than their envelopes and become susceptible to instabilities even when the whole jet is stable. This may result in local dissipation and emission without global disintegration of the flow. Cosmic jets may become globally unstable when they enter at sections of external atmospheres. We propose that the Fanaro -Riley morphological division of extragalactic radio sources into two classes is related to this issue. In particular, we argue that the low power FR-I jets become re-confined, causally connected and globally unstable on the scale of galactic X-ray coronas, whereas more powerful FR-II jets re-confine much further out, already on the scale of radio lobes, and remain largely intact until they terminate at hot spots. Using this idea, we derived the relationship between the critical jet power and the optical luminosity of the host galaxy, which is in a very good agreement with the observations.