超新星纳米粒子中的富中子铬同位素异常
Neutron-rich chromium isotope anomalies in supernova nanoparticles
摘要：
质量接近铁的富中子同位素是在Ia型和II型超新星中产生的。这种核合成的痕迹在原始陨石中以54 Cr同位素丰度变化的形式被发现，54 Cr是铬的最富中子的稳定同位素。这些同位素异常的宿主一定是在超新星流出时凝聚的前太阳颗粒，这为研究铁峰核的核合成提供了机会，补充了光谱观测，并为恒星演化模型提供了信息。然而，尽管近二十年的广泛搜索，54 Cr异常的载体仍然是未知的，大概是因为它是细粒度的，是化学不稳定的。在这里，我们在原始陨石Orgueil中确定了54 Cr异常的载体为纳米颗粒，最有可能的是相对于太阳能成分显示出大量富集54 Cr的尖晶石（54 Cr/52 Cr比率> 3.6x太阳能）。如此大的54 Cr丰度只有在超新星中才能产生。颗粒的矿物学支持II型超新星的O/Ne-O/C区的凝聚，尽管不能排除Ia型起源。我们认为，行星材料中含有不同数量的这些纳米粒子，可能是由于附近的超新星晚期注入，也将26 Al和60 Fe输送到太阳系。这个想法解释了为什么54 Cr和其他富含中子的同位素的相对丰度在行星和陨石之间存在差异。我们预计，未来对这些颗粒的同位素研究将为太阳系的诞生和超新星的形成提供新的线索。
英文摘要：
Neutron-rich isotopes with masses near that of iron are produced in type Ia and II supernovae. Traces of such nucleosynthesis are found in primitive meteorites in the form of variations in the isotopic abundance of 54Cr, the most neutron-rich stable isotope of chromium. The hosts of these isotopic anomalies must be presolar grains that condensed in the outflows of supernovae, offering the opportunity to study the nucleosynthesis of iron-peak nuclei in ways that complement spectroscopic observations and can inform models of stellar evolution. However, despite almost two decades of extensive search, the carrier of 54Cr anomalies is still unknown, presumably because it is fine-grained and is chemically labile. Here we identify in the primitive meteorite Orgueil the carrier of 54Cr-anomalies as nanoparticles, most likely spinels that show large enrichments in 54Cr relative to solar composition (54Cr/52Cr ratio >3.6xsolar). Such large enrichments in 54Cr can only be produced in supernovae. The mineralogy of the grains supports condensation in the O/Ne-O/C zones of a type II supernova, although a type Ia origin cannot be excluded. We suggest that planetary materials incorporated different amounts of these nanoparticles, possibly due to late injection by a nearby supernova that also delivered 26Al and 60Fe to the solar system. This idea explains why the relative abundance of 54Cr and other neutron-rich isotopes vary between planets and meteorites. We anticipate that future isotopic studies of the grains identified here will shed new light on the birth of the solar system and the conditions insupernovae.
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