The trouble with the Local Bubble
The trouble with the Local Bubble
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局部泡沫的麻烦
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
Robin L. Shelton
中科院分区：
文献类型：
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作者：
B. Welsh;Robin L. Shelton
局部热泡模型已被广泛接受，因为它提供了一个框架，可以解释软X射线背景漫发射的普遍存在。我们总结了目前的知识，在这个地方的星际区域，特别提到的意见，样品发射从假定的本地百万度K热等离子体。然而，我们已经列出了许多观察结果，这些观察结果似乎与热局部泡沫的概念相冲突。特别是，太阳风电荷交换的发现，可以产生一个可观的软X射线背景信号的日光层内，导致了重新评估的普遍接受的模型，需要一个热的本地plasma.为了解释大多数观测的本地plasma，我们提出了两个新的投机模型，描述的物理状态的本地星际气体。一种可能的情况类似于目前广泛接受的局部热泡模型，除了它只占目前在银道面探测到的软X射线发射的50%，具有比以前认为的更低的热压，并且它的热等离子体不像以前认为的那样热。虽然这样的模型可以解决传统的热局部气泡模型的几个困难，一个较暗和较冷的气体的加热机制仍然有待发现。第二个可能的解释是'热顶'模型，其中局部空腔是一个古老的超新星遗迹，其中没有（或很少）百万度的局部等离子体目前需要。相反，现在认为这个空腔充满了温度为7000 K的部分电离云，这些云被温度为20,000 K的光电离气体的低密度包层包围。虽然这种新的情况下提供了一个自然的解释，许多观察是在冲突的本地热泡模型，我们不能（到目前为止）提供一个令人满意的解释或在B和Be超软X射线波段观察到的发射水平。
The model of a Local Hot Bubble has been widely accepted as providing a framework that can explain the ubiquitous presence of the soft X-ray background diffuse emission. We summarize the current knowledge on this local interstellar region, paying particular reference to observations that sample emission from the presumed local million degree K hot plasma. However, we have listed numerous observations that are seemingly in conflict with the concept of a hot Local Bubble. In particular, the discovery of solar wind charge exchange that can generate an appreciable soft X-ray background signal within the heliosphere, has led to a re-assessment of the generally accepted model that requires a hot local plasma.In order to explain the majority of observations of the local plasma, we forward two new speculative models that describe the physical state of the local interstellar gas. One possible scenario is similar to the present widely accepted model of the Local Hot Bubble, except that it accounts for only 50% of the soft X-ray emission currently detected in the galactic plane, has a lower thermal pressure than previously thought, and its hot plasma is not as hot as previously believed. Although such a model can solve several difficulties with the traditional hot Local Bubble model, a heating mechanism for the dimmer and cooler gas remains to be found. The second possible explanation is that of the ‘Hot Top’ model, in which the Local Cavity is an old supernova remnant in which no (or very little) million degree local plasma is presently required. Instead, the cavity is now thought to be filled with partially ionized cloudlets of temperature ∼7000 K that are surrounded by lower density envelopes of photo-ionized gas of temperature ∼20,000 K. Although this new scenario provides a natural explanation for many of the observations that were in conflict with the Local Hot Bubble model, we cannot (as yet) provide a satisfactory explanation or the emission levels observed in the B and Be ultra-soft X-ray bands.