世界看热讯：《自然》（20230622出版）一周论文导读

编译 | 冯维维

Nature, Volume 618 Issue 7966, 22 June 2023

(相关资料图)

《自然》第618卷，7966期，2023年6月22日

天体物理学和天体化学Astrophysics & Astrochemistry

Spatial variations in aromatic hydrocarbon emission in a dust-rich galaxy

富尘埃星系中芳香烃排放的空间变化

▲ 作者：Justin S. Spilker, Kedar A. Phadke, Manuel Aravena, Melanie Archipley, Matthew B. Bayliss, Jack E. Birkin, Matthieu Béthermin, James Burgoyne, Jared Cathey, Scott C. Chapman, H?kon Dahle, Anthony H. Gonzalez, Gayathri Gururajan, Christopher C. Hayward, Yashar D. Hezaveh, Ryley Hill, Taylor A. Hutchison, Keunho J. Kim, Seonwoo Kim, David Law, Ronan Legin, Matthew A. Malkan, Daniel P. Marrone, Eric J. Murphy, …Katherine E. Whitaker Show authors

▲ 链接：

https://www.nature.com/articles/s41586-023-05998-6

▲ 摘要：

在整个宇宙历史中，尘埃颗粒吸收了恒星发出的一半辐射，并以红外波长重新发射这些能量。多环芳烃（PAHs）是一种大型有机分子，可追踪毫米大小的尘埃颗粒，并调节星系内星际气体的冷却。由于以前的红外望远镜的灵敏度和波长覆盖范围有限，在非常遥远的星系中观测多环芳烃的特征一直很困难。研究者展示了詹姆斯韦伯太空望远镜在大爆炸后不到15亿年观测到的星系中探测到3.3 μm多环芳香烷特征的观测结果。多环芳烃特征的高等效宽度表明，整个星系的红外发射主要是恒星形成，而不是黑洞吸积。

多环芳烃分子、热尘埃、大尘埃颗粒和恒星发出的光在空间上彼此不同，导致多环芳烃等效宽度和多环芳烃与整个星系的总红外光度之比发生了数量级的变化。研究者观察到的空间变化表明，多环芳烃与大尘埃颗粒之间存在物理偏移，或者在局部紫外线辐射场中存在较大差异。我们的观察表明，多环芳烃分子和大尘埃颗粒的发射差异是早期星系局部过程的复杂结果。

▲ Abstract：

Dust grains absorb half of the radiation emitted by stars throughout the history of the universe, re-emitting this energy at infrared wavelengths. Polycyclic aromatic hydrocarbons (PAHs) are large organic molecules that trace millimetre-size dust grains and regulate the cooling of interstellar gas within galaxies. Observations of PAH features in very distant galaxies have been difficult owing to the limited sensitivity and wavelength coverage of previous infrared telescopes. Here we present James Webb Space Telescope observations that detect the 3.3?μm PAH feature in a galaxy observed less than 1.5?billion years after the Big Bang. The high equivalent width of the PAH feature indicates that star formation, rather than black hole accretion, dominates infrared emission throughout the galaxy. The light from PAH molecules, hot dust and large dust grains and stars are spatially distinct from one another, leading to order-of-magnitude variations in PAH equivalent width and ratio of PAH to total infrared luminosity across the galaxy. The spatial variations we observe suggest either a physical offset between PAHs and large dust grains or wide variations in the local ultraviolet radiation field. Our observations demonstrate that differences in emission from PAH molecules and large dust grains are a complex result of localized processes within early galaxies.

A metal-poor star with abundances from a pair-instability supernova

贫金属恒星金属丰度来自一对不稳定的超新星

▲ 作者：Qian-Fan Xing, Gang Zhao, Zheng-Wei Liu, Alexander Heger, Zhan-Wen Han, Wako Aoki, Yu-Qin Chen, Miho N. Ishigaki, Hai-Ning Li & Jing-Kun Zhao

▲ 链接：

https://www.nature.com/articles/s41586-023-06028-1

▲ 摘要：

质量最大、寿命最短的恒星主导着前银河系时代的化学演化。在数值模拟的基础上，人们早就推测这类第一代恒星的质量可达数百个太阳质量。

超大质量的第一代恒星的质量范围在140到260太阳质量之间，预计会通过对不稳定超新星丰富早期星际介质。然而，经过几十年的观测努力，尚未能独特识别出如此巨大的恒星在银河系中最缺乏金属的恒星上留下的印记。

研究者报告了一颗极低钠和钴丰度的金属极贫恒星的化学成分。这颗恒星中钠与铁的比值比太阳低两个数量级以上。这颗恒星的奇电荷数和偶电荷数元素的丰度差异非常大，比如钠/镁和钴/镍。

这种奇特的奇偶效应，加上钠和α元素的缺乏，与对质量超过140个太阳质量的恒星产生的原始对不稳定超新星的预测相一致。这提供了一个清晰的化学特征，表明早期宇宙中存在非常大质量的恒星。

▲ Abstract：

The most massive and shortest-lived stars dominate the chemical evolution of the pre-galactic era. On the basis of numerical simulations, it has long been speculated that the mass of such first-generation stars was up to several hundred solar masses1,2,3,4. The very massive first-generation stars with a mass range from 140 to 260 solar masses are predicted to enrich the early interstellar medium through pair-instability supernovae (PISNe). Decades of observational efforts, however, have not been able to uniquely identify the imprints of such very massive stars on the most metal-poor stars in the Milky Way. Here we report the chemical composition of a very metal-poor (VMP) star with extremely low sodium and cobalt abundances. The sodium with respect to iron in this star is more than two orders of magnitude lower than that of the Sun. This star exhibits very large abundance variance between the odd- and even-charge-number elements, such as sodium/magnesium and cobalt/nickel. Such peculiar odd–even effect, along with deficiencies of sodium and α elements, are consistent with the prediction of primordial pair-instability supernova (PISN) from stars more massive than 140 solar masses. This provides a clear chemical signature indicating the existence of very massive stars in the early universe.

物理学Physics

Density-wave ordering in a unitary Fermi gas with photon-mediated interactions

具有光子介导相互作用的单一费米气体中的密度波有序

▲ 作者：Victor Helson, Timo Zwettler, Farokh Mivehvar, Elvia Colella, Kevin Roux, Hideki Konishi, Helmut Ritsch & Jean-Philippe Brantut

▲ 链接：

https://www.nature.com/articles/s41586-023-06018-3

▲ 摘要：

密度波（DW）是量子物质中一种基本的长程秩序，与晶体结构的自组织有关。DW阶与超流动性的相互作用会导致复杂的情况，这对理论分析提出了很大的挑战。

过去几十年，可调谐量子费米气体已经成为探索强相互作用费米子物理学的模型系统，包括最著名的磁有序、配对和超流动性，以及从巴丁-库珀-施里弗超流体到玻色-爱因斯坦凝聚体的交叉。

研究者在横向驱动的高精细光学腔中实现了具有强的、可调谐的接触相互作用和光子介导的、空间结构的远程相互作用的费米气体。

在一个临界的远程相互作用强度之上，DW阶在系统中是稳定的，研究者通过其超辐射光散射特性来识别。他们定量地测量了接触相互作用在巴丁-库珀-徐瑞弗超流体和玻色-爱因斯坦凝聚交叉中发生变化时DW阶的开始变化，定性地与平均场理论一致。将远距相互作用的强度和符号调整到低于自排序阈值时，原子DW磁化率变化超过一个数量级，表明对接触和远距相互作用的独立和同时控制。研究者表示，该实验装置为超流体与DW阶序相互作用的实验研究提供了一个完全可调和微观可控的平台。

▲ Abstract：

A density wave (DW) is a fundamental type of long-range order in quantum matter tied to self-organization into a crystalline structure. The interplay of DW order with superfluidity can lead to complex scenarios that pose a great challenge to theoretical analysis. In the past decades, tunable quantum Fermi gases have served as model systems for exploring the physics of strongly interacting fermions, including most notably magnetic ordering, pairing and superfluidity, and the crossover from a Bardeen–Cooper–Schrieffer superfluid to a Bose–Einstein condensate. Here, we realize a Fermi gas featuring both strong, tunable contact interactions and photon-mediated, spatially structured long-range interactions in a transversely driven high-finesse optical cavity. Above a critical long-range interaction strength, DW order is stabilized in the system, which we identify via its superradiant light-scattering properties. We quantitatively measure the variation of the onset of DW order as the contact interaction is varied across the Bardeen–Cooper–Schrieffer superfluid and Bose–Einstein condensate crossover, in qualitative agreement with a mean-field theory. The atomic DW susceptibility varies over an order of magnitude upon tuning the strength and the sign of the long-range interactions below the self-ordering threshold, demonstrating independent and simultaneous control over the contact and long-range interactions. Therefore, our experimental setup provides a fully tunable and microscopically controllable platform for the experimental study of the interplay of superfluidity and DW order.

Quantum-limited optical time transfer for future geosynchronous links

未来地球同步链路的量子限制光时间传输

▲ 作者：Emily D. Caldwell, Jean-Daniel Deschenes, Jennifer Ellis, William C. Swann, Benjamin K. Stuhl, Hugo Bergeron, Nathan R. Newbury & Laura C. Sinclair

▲ 链接：

https://www.nature.com/articles/s41586-023-06032-5

▲ 摘要：

光时间传输和光时钟的结合，为连接地面光时钟和未来天基光时钟的大规模自由空间网络开辟了可能性。这样的网络有望更好地测试广义相对论、暗物质搜索和引力波探测。

将光学时钟连接到远程卫星的能力可以实现天基超长基线干涉测量、先进的卫星导航、基于时钟的大地测量以及洲际时间传播的数千倍改进。

到目前为止，只有光学时钟朝着量子限制性能的方向发展。相比之下，光时间传递没有在由接收光子数量设定的类似量子极限下运行。研究者展示了时间传输与近量子限制的采集和定时比以前的方法低10000倍的接收功率。

夏威夷山顶之间的距离超过300公里，发射功率低至40微瓦，远距离站点同步到320阿秒。这种近乎量子限制的操作对于光子少且放大成本高的长距离自由空间链路至关重要：在4.0 mW的发射功率下，这种方法可以支持102 dB的链路损耗，足以在未来将时间传输到地球同步轨道。

▲ Abstract：

The combination of optical time transfer and optical clocks opens up the possibility of large-scale free-space networks that connect both ground-based optical clocks and future space-based optical clocks. Such networks promise better tests of general relativity, dark-matter searches and gravitational-wave detection. The ability to connect optical clocks to a distant satellite could enable space-based very long baseline interferometry, advanced satellite navigation, clock-based geodesy and thousandfold improvements in intercontinental time dissemination. Thus far, only optical clocks have pushed towards quantum-limited performance. By contrast, optical time transfer has not operated at the analogous quantum limit set by the number of received photons. Here we demonstrate time transfer with near quantum-limited acquisition and timing at 10,000 times lower received power than previous approaches. Over 300?km between mountaintops in Hawaii with launched powers as low as 40 μW, distant sites are synchronized to 320 attoseconds. This nearly quantum-limited operation is critical for long-distance free-space links in which photons are few and amplification costly: at 4.0mW transmit power, this approach can support 102?dB link loss, more than sufficient for future time transfer to geosynchronous orbits.

地球物理学Geophysics

Increasingly negative tropical water–interannual CO2 growth rate coupling

束热带水-年际二氧化碳日益增加的富增长率耦合

▲ 作者：Laibao Liu, Philippe Ciais, Mengxi Wu, Ryan S. Padrón, Pierre Friedlingstein, Jonas Schwaab, Lukas Gudmundsson & Sonia I. Seneviratne

▲ 链接：

https://www.nature.com/articles/s41586-023-06056-x

▲ 摘要：

过去60年，陆地生态系统已经吸收了约32%的人为二氧化碳（CO2）排放总量。然而，陆地碳-气候反馈的巨大不确定性使得预测陆地碳汇如何响应未来的气候变化变得困难。

热带地区大气CO2增长率（CGR）的年际变化主要由陆地-大气碳通量主导，这为探索陆地-气候相互作用提供了机会。

科学家认为CGR的变化在很大程度上受温度控制，但也有证据表明，水的可用性和CGR11之间存在紧密耦合。研究者利用全球大气CO2记录、陆地储水量和降水数据，研究了气候变化下热带陆地气候条件与CGR的年际关系变化。

他们发现，与1960-1989年相比，1989-2018年热带水资源可得性与CGR的年际关系变得越来越负。这可能与厄尔尼诺/南方涛动遥相关变化驱动的热带水可用性异常的时空变化有关，包括空间补偿性水效应的减弱。

研究还证明，大多数最先进的地球系统和陆地表面耦合模型不能再现水-碳耦合的加剧。研究结果表明，热带水分可得性正日益控制着陆地碳循环的年际变化，并调节着热带陆地碳-气候反馈。

▲ Abstract：

Terrestrial ecosystems have taken up about 32% of the total anthropogenic CO2 emissions in the past six decades. Large uncertainties in terrestrial carbon–climate feedbacks, however, make it difficult to predict how the land carbon sink will respond to future climate change. Interannual variations in the atmospheric CO2 growth rate (CGR) are dominated by land–atmosphere carbon fluxes in the tropics, providing an opportunity to explore land carbon–climate interactions. It is thought that variations in CGR are largely controlled by temperature but there is also evidence for a tight coupling between water availability and CGR11. Here, we use a record of global atmospheric CO2, terrestrial water storage and precipitation data to investigate changes in the interannual relationship between tropical land climate conditions and CGR under a changing climate. We find that the interannual relationship between tropical water availability and CGR became increasingly negative during 1989–2018 compared to 1960–1989. This could be related to spatiotemporal changes in tropical water availability anomalies driven by shifts in El Ni?o/Southern Oscillation teleconnections, including declining spatial compensatory water effects. We also demonstrate that most state-of-the-art coupled Earth System and Land Surface models do not reproduce the intensifying water–carbon coupling. Our results indicate that tropical water availability is increasingly controlling the interannual variability of the terrestrial carbon cycle and modulating tropical terrestrial carbon–climate feedbacks.

Major southern San Andreas earthquakes modulated by lake-filling events

南部圣安地列斯地震由湖泊填充事件调制

▲ 作者：Ryley G. Hill, Matthew Weingarten, Thomas K. Rockwell & Yuri Fialko

▲ 链接：

https://www.nature.com/articles/s41586-023-06058-9

▲ 摘要：

水文荷载可以刺激地壳的地震活动性。然而，引发大地震的证据仍然难以捉摸。南加州的南圣安德烈亚斯断层（SSAF）毗邻萨尔顿海，这是古卡韦拉湖的遗迹，在过去一千年里，它周期性地充满并干涸。

本文利用新的地质和古地震资料证明，过去6次大地震可能发生在卡韦拉湖的高点。为了研究可能的因果关系，研究者计算了湖泊水位变化引起的库仑应力随时间的变化。

利用黏弹性地幔上的孔弹性地壳的完全耦合模型，研究者发现水文荷载使SSAF上的库仑应力增加了几百千帕斯卡，断层应力率增加了2倍以上，这可能足以引发地震。

非垂直断层倾角、断层破坏带的存在和侧向孔隙压力扩散增强了湖泊淹没的不稳定效应。我们的模型可能适用于其他地区的水文负荷，无论是自然的还是人为的，都与大量的地震活动有关。

▲ Abstract：

Hydrologic loads can stimulate seismicity in the Earth’s crust. However, evidence for the triggering of large earthquakes remains elusive. The southern San Andreas Fault (SSAF) in Southern California lies next to the Salton Sea, a remnant of ancient Lake Cahuilla that periodically filled and desiccated over the past millennium. Here we use new geologic and palaeoseismic data to demonstrate that the past six major earthquakes on the SSAF probably occurred during highstands of Lake Cahuilla. To investigate possible causal relationships, we computed time-dependent Coulomb stress changes due to variations in the lake level. Using a fully coupled model of a poroelastic crust overlying a viscoelastic mantl, we find that hydrologic loads increased Coulomb stress on the SSAF by several hundred kilopascals and fault-stressing rates by more than a factor of 2, which is probably sufficient for earthquake triggering. The destabilizing effects of lake inundation are enhanced by a nonvertical fault dip, the presence of a fault damage zone and lateral pore-pressure diffusion. Our model may be applicable to other regions in which hydrologic loading, either natural or anthropogenic, was associated with substantial seismicity.

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