原恒星：宇宙射线的锻造？
Protostars: Forges of cosmic rays?
摘要：
银河系宇宙射线（CR）是一种在超新星残余激波中加速的粒子，在星际介质中传播到分子云的致密部分，由于磁场的存在和与分子氢的碰撞，损失了能量和电离效率。最近的观测暗示在高水平的电离和同步辐射的存在下，在原恒星系统，这导致了一个明显的矛盾。我们想解释的起源，这些CR加速内年轻的原恒星所建议的意见。我们的建模包括一组条件，必须满足，以便有一个有效的CR加速通过扩散冲击加速。我们分析了三个主要的加速站点，然后我们遵循这些粒子通过原恒星系统的热点区域的传播。我们发现，射流冲击可以CR质子，这可以提高到相对论能量的强加速器。其他有希望的加速地点是原恒星表面，在坍缩阶段由撞击物质引起的冲击足以加速CR质子。相比之下，吸积流激波太弱，不能有效地加速CR。虽然CR电子被弱加速，但它们可以通过连续冲击中的再加速获得相对论能量的强烈提升。我们提出了一种机制，能够加速CR质子和电子通过扩散冲击加速机制，这可以用来解释高电离率和同步辐射观测到对原恒星源。高能粒子的内部来源的存在可能会对原恒星盘的电离、恒星和行星形成过程以及前生物分子的形成产生强烈的和不可预见的影响。
英文摘要：
Galactic cosmic rays (CR) are particles presumably accelerated in supernova remnant shocks that propagate in the interstellar medium up to the densest parts of molecular clouds, losing energy and their ionisation efficiency because of the presence of magnetic fields and collisions with molecular hydrogen. Recent observations hint at high levels of ionisation and at the presence of synchrotron emission in protostellar systems, which leads to an apparent contradiction. We want to explain the origin of these CRs accelerated within young protostars as suggested by observations. Our modelling consists of a set of conditions that has to be satisfied in order to have an efficient CR acceleration through diffusive shock acceleration. We analyse three main acceleration sites, then we follow the propagation of these particles through the protostellar system up to the hot spot region. We find that jet shocks can be strong accelerators of CR protons, which can be boosted up to relativistic energies. Other promising acceleration sites are protostellar surfaces, where shocks caused by impacting material during the collapse phase are strong enough to accelerate CR protons. In contrast, accretion flow shocks are too weak to efficiently accelerate CRs. Though CR electrons are weakly accelerated, they can gain a strong boost to relativistic energies through re-acceleration in successive shocks. We suggest a mechanism able to accelerate both CR protons and electrons through the diffusive shock acceleration mechanism, which can be used to explain the high ionisation rate and the synchrotron emission observed towards protostellar sources. The existence of an internal source of energetic particles can have a strong and unforeseen impact on the ionisation of the protostellar disc, on the star and planet formation processes, and on the formation of pre-biotic molecules.
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