r-Process Radioisotopes from Near-Earth Supernovae and Kilonovae

The astrophysical sites where r-process elements are synthesized remain mysterious: it is clear that neutron star mergers (kilonovae (KNe)) contribute, and some classes of core-collapse supernovae (SNe) are also possible sources of at least the lighter r-process species. The discovery of 60Fe on the Earth and Moon implies that one or more astrophysical explosions have occurred near the Earth within the last few million years, probably SNe. Intriguingly, 244Pu has now been detected, mostly overlapping with 60Fe pulses. However, the 244Pu flux may extend to before 12 Myr ago, pointing to a different origin. Motivated by these observations and difficulties for r-process nucleosynthesis in SN models, we propose that ejecta from a KN enriched the giant molecular cloud that gave rise to the Local Bubble, where the Sun resides. Accelerator mass spectrometry (AMS) measurements of 244Pu and searches for other live isotopes could probe the origins of the r-process and the history of the solar neighborhood, including triggers for mass extinctions, e.g., that at the end of the Devonian epoch, motivating the calculations of the abundances of live r-process radioisotopes produced in SNe and KNe that we present here. Given the presence of 244Pu, other r-process species such as 93Zr, 107Pd, 129I, 135Cs, 182Hf, 236U, 237Np, and 247Cm should be present. Their abundances and well-resolved time histories could distinguish between the SN and KN scenarios, and we discuss prospects for their detection in deep-ocean deposits and the lunar regolith. We show that AMS 129I measurements in Fe–Mn crusts already constrain a possible nearby KN scenario.

r - 过程元素合成的天体物理场所仍然是个谜：很明显，中子星并合（千新星（KNe））有贡献，并且某些类型的核心坍缩超新星（SNe）也可能是至少较轻的r - 过程种类的来源。在地球和月球上发现的铁 - 60意味着在过去几百万年里地球附近发生了一次或多次天体物理爆炸，可能是超新星爆发。有趣的是，现在已经探测到钚 - 244，且大多与铁 - 60脉冲重叠。然而，钚 - 244通量可能延伸到1200万年前，这指向一个不同的起源。受这些观测结果以及超新星模型中r - 过程核合成的困难所推动，我们提出千新星的抛射物使产生本星系泡（太阳所在之处）的巨分子云变得富集。对钚 - 244的加速器质谱（AMS）测量以及对其他放射性同位素的搜寻可以探究r - 过程的起源以及太阳邻域的历史，包括大规模灭绝的触发因素，例如泥盆纪末期的那次，这促使我们在此给出超新星和千新星中产生的放射性r - 过程放射性同位素丰度的计算。鉴于钚 - 244的存在，其他r - 过程种类，如锆 - 93、钯 - 107、碘 - 129、铯 - 135、铪 - 182、铀 - 236、镎 - 237和锔 - 247应该存在。它们的丰度以及清晰的时间历史可以区分超新星和千新星的情景，并且我们讨论了在深海沉积物和月球风化层中探测它们的前景。我们表明，在铁 - 锰结壳中进行的加速器质谱碘 - 129测量已经对附近可能的千新星情景施加了限制。