永远年轻的白矮星：当恒星老化停止时
Forever young white dwarfs: when stellar ageing stops
摘要：
白矮星是恒星演化最常见的终点。特别令人感兴趣的是超大质量的白矮星，因为它们与Ia型超新星爆炸、合并事件和快速射电暴有关。超大质量白矮星被认为是单一标准恒星演化的结果，拥有氧氖（ONe）核。然而，它们中的一小部分可能具有碳氧（CO）核心。最近根据{ \it Gaia}空间飞行任务提供的新观测结果进行的研究表明，一小部分超大质量白矮星在冷却过程中经历了强烈的延迟，这不能仅仅归因于结晶的发生，因此需要一种能够长期延长其寿命的未知能源。在这项研究中，我们发现，$^{22}$ Ne沉积释放的能量在内部深处的超大质量白矮星与CO核心和高$^{22}$ Ne含量是一致的，这些恒星残留物的冷却延迟长。在综合研究白矮星星族的基础上，基于Monte Carlo技术，我们发现，{ \it Gaia}揭示的观测结果可以用这些长期年轻的超大质量白矮星的存在来解释。虽然如此高的$^{22}$ Ne丰度与标准的演化通道不一致，但我们的结果支持了CO核超大质量白矮星的存在和$^{22}$ Ne沉积的发生.
英文摘要：
White dwarf stars are the most common end point of stellar evolution. Of special interest are the ultramassive white dwarfs, as they are related to type Ia Supernovae explosions, merger events, and Fast Radio Bursts. Ultramassive white dwarfs are expected to harbour oxygen-neon (ONe) cores as a result of single standard stellar evolution. However, a fraction of them could have carbon-oxygen (CO) cores. Recent studies, based on the new observations provided by the {\it Gaia} space mission, indicate that a small fraction of the ultramassive white dwarfs experience a strong delay in their cooling, which cannot be attributed only to the occurrence of crystallization, thus requiring an unknown energy source able to prolong their life for long periods of time. In this study we find that the energy released by $^{22}$Ne sedimentation in the deep interior of ultramassive white dwarfs with CO cores and high $^{22}$Ne content is consistent with the long cooling delay of these stellar remnants. On the basis of a synthesis study of the white dwarf population, based on Monte Carlo techniques, we find that the observations revealed by {\it Gaia} can be explained by the existence of these prolonged youth ultramassive white dwarfs. Although such a high $^{22}$Ne abundance is not consistent with the standard evolutionary channels, our results provide sustain to the existence of CO-core ultramassive white dwarfs and to the occurrence of $^{22}$Ne sedimentation.
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