银河系中心磁盘的碎片过去：失踪红巨星的罪魁祸首
The fragmenting past of the disk at the Galactic Center : The culprit for the missing red giants
摘要：
自1996年以来，我们已经知道银河系中心（GC）显示了一个类似核心的红巨星分支（RGB）恒星分布，从~ 10”开始，这提出了一个理论问题，因为GC应该形成了一个分离的老恒星尖点。这个问题已经得到解决，调用恒星碰撞，大质量黑洞双星，并陷入星团，这可以在一定程度上解释它。另一个观测事实，这里提出的工作的关键，是在GC恒星盘的存在。我们假设RGB中缺少恒星的原因与盘的形成密切相关，盘最初是气态的，并经历了碎片化阶段形成恒星。使用简单的分析估计，我们证明，在破碎的磁盘开发区域的密度远高于均匀的气体磁盘，即“团块”，这是光学厚，因此收缩缓慢。GC中的恒星与它们相互作用，在RGB恒星的情况下，团块的密度足以在相对较低的撞击次数后完全去除它们的外层。然而，水平分支（HB）中的巨星有更致密的外壳。因此，磁盘的碎片化阶段对它们的分布的影响一定较小，因为更难去除它们的封套。我们预测，未来更深入的观察GC应该揭示较少的HB星的耗尽和释放的致密核心的RGB星仍将填充GC。
英文摘要：
Since 1996 we have known that the Galactic Center (GC) displays a core-like distribution of red giant branch (RGB) stars starting at ~ 10", which poses a theoretical problem, because the GC should have formed a segregated cusp of old stars. This issue has been addressed invoking stellar collisions, massive black hole binaries, and infalling star clusters, which can explain it to some extent. Another observational fact, key to the work presented here, is the presence of a stellar disk at the GC. We postulate that the reason for the missing stars in the RGB is closely intertwined with the disk formation, which initially was gaseous and went through a fragmentation phase to form the stars. Using simple analytical estimates, we prove that during fragmentation the disk developed regions with densities much higher than a homogeneous gaseous disk, i.e. "clumps", which were optically thick, and hence contracted slowly. Stars in the GC interacted with them and in the case of RGB stars, the clumps were dense enough to totally remove their outer envelopes after a relatively low number of impacts. Giant stars in the horizontal branch (HB), however, have much denser envelopes. Hence, the fragmentation phase of the disk must have had a lower impact in their distribution, because it was more difficult to remove their envelopes. We predict that future deeper observations of the GC should reveal less depletion of HB stars and that the released dense cores of RGB stars will still be populating the GC.
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