原文地址：http://news.sciencenet.cn/htmlnews/2023/6/503416.shtm
編譯 | 馮維維
Nature, Volume 618 Issue 7966, 22 June 2023
《自然》第618卷，7966期，2023年6月22日
天體物理學和天體化學Astrophysics & Astrochemistry
Spatial variations in aromatic hydrocarbon emission in a dust-rich galaxy
富塵埃星系中芳香烴排放的空間變化
▲ 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
▲ 鏈接：
https://www.nature.com/articles/s41586-023-05998-6
▲ 摘要：
在整個宇宙歷史中，塵埃顆粒吸收了恒星發出的一半輻射，并以紅外波長重新發射這些能量。多環芳烴（PAHs）是一種大型有機分子，可追蹤毫米大小的塵埃顆粒，并調節星系內星際氣體的冷卻。由于以前的紅外望遠鏡的靈敏度和波長覆蓋范圍有限，在非常遙遠的星系中觀測多環芳烴的特征一直很困難。研究者展示了詹姆斯韋伯太空望遠鏡在大爆炸后不到15億年觀測到的星系中探測到3.3 μm多環芳香烷特征的觀測結果。多環芳烴特征的高等效寬度表明，整個星系的紅外發射主要是恒星形成，而不是黑洞吸積。
多環芳烴分子、熱塵埃、大塵埃顆粒和恒星發出的光在空間上彼此不同，導致多環芳烴等效寬度和多環芳烴與整個星系的總紅外光度之比發生了數量級的變化。研究者觀察到的空間變化表明，多環芳烴與大塵埃顆粒之間存在物理偏移，或者在局部紫外線輻射場中存在較大差異。我們的觀察表明，多環芳烴分子和大塵埃顆粒的發射差異是早期星系局部過程的復雜結果。
▲ 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
貧金屬恒星金屬豐度來自一對不穩定的超新星
▲ 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
▲ 鏈接：
https://www.nature.com/articles/s41586-023-06028-1
▲ 摘要：
質量最大、壽命最短的恒星主導著前銀河系時代的化學演化。在數值模擬的基礎上，人們早就推測這類第一代恒星的質量可達數百個太陽質量。
超大質量的第一代恒星的質量范圍在140到260太陽質量之間，預計會通過對不穩定超新星豐富早期星際介質。然而，經過幾十年的觀測努力，尚未能獨特識別出如此巨大的恒星在銀河系中最缺乏金屬的恒星上留下的印記。
研究者報告了一顆極低鈉和鈷豐度的金屬極貧恒星的化學成分。這顆恒星中鈉與鐵的比值比太陽低兩個數量級以上。這顆恒星的奇電荷數和偶電荷數元素的豐度差異非常大，比如鈉/鎂和鈷/鎳。
這種奇特的奇偶效應，加上鈉和α元素的缺乏，與對質量超過140個太陽質量的恒星產生的原始對不穩定超新星的預測相一致。這提供了一個清晰的化學特征，表明早期宇宙中存在非常大質量的恒星。
▲ 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.
物理學Physics
Density-wave ordering in a unitary Fermi gas with photon-mediated interactions
具有光子介導相互作用的單一費米氣體中的密度波有序
▲ 作者：Victor Helson, Timo Zwettler, Farokh Mivehvar, Elvia Colella, Kevin Roux, Hideki Konishi, Helmut Ritsch & Jean-Philippe Brantut
▲ 鏈接：
https://www.nature.com/articles/s41586-023-06018-3
▲ 摘要：
密度波（DW）是量子物質中一種基本的長程秩序，與晶體結構的自組織有關。DW階與超流動性的相互作用會導致復雜的情況，這對理論分析提出了很大的挑戰。
過去幾十年，可調諧量子費米氣體已經成為探索強相互作用費米子物理學的模型系統，包括最著名的磁有序、配對和超流動性，以及從巴丁-庫珀-施里弗超流體到玻色-愛因斯坦凝聚體的交叉。
研究者在橫向驅動的高精細光學腔中實現了具有強的、可調諧的接觸相互作用和光子介導的、空間結構的遠程相互作用的費米氣體。
在一個臨界的遠程相互作用強度之上，DW階在系統中是穩定的，研究者通過其超輻射光散射特性來識別。他們定量地測量了接觸相互作用在巴丁-庫珀-徐瑞弗超流體和玻色-愛因斯坦凝聚交叉中發生變化時DW階的開始變化，定性地與平均場理論一致。將遠距相互作用的強度和符號調整到低于自排序閾值時，原子DW磁化率變化超過一個數量級，表明對接觸和遠距相互作用的獨立和同時控制。研究者表示，該實驗裝置為超流體與DW階序相互作用的實驗研究提供了一個完全可調和微觀可控的平臺。
▲ 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
未來地球同步鏈路的量子限制光時間傳輸
▲ 作者：Emily D. Caldwell, Jean-Daniel Deschenes, Jennifer Ellis, William C. Swann, Benjamin K. Stuhl, Hugo Bergeron, Nathan R. Newbury & Laura C. Sinclair
▲ 鏈接：
https://www.nature.com/articles/s41586-023-06032-5
▲ 摘要：
光時間傳輸和光時鐘的結合，為連接地面光時鐘和未來天基光時鐘的大規模自由空間網絡開辟了可能性。這樣的網絡有望更好地測試廣義相對論、暗物質搜索和引力波探測。
將光學時鐘連接到遠程衛星的能力可以實現天基超長基線干涉測量、先進的衛星導航、基于時鐘的大地測量以及洲際時間傳播的數千倍改進。
到目前為止，只有光學時鐘朝著量子限制性能的方向發展。相比之下，光時間傳遞沒有在由接收光子數量設定的類似量子極限下運行。研究者展示了時間傳輸與近量子限制的采集和定時比以前的方法低10000倍的接收功率。
夏威夷山頂之間的距離超過300公里，發射功率低至40微瓦，遠距離站點同步到320阿秒。這種近乎量子限制的操作對于光子少且放大成本高的長距離自由空間鏈路至關重要：在4.0 mW的發射功率下，這種方法可以支持102 dB的鏈路損耗，足以在未來將時間傳輸到地球同步軌道。
▲ 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.
地球物理學Geophysics
Increasingly negative tropical water–interannual CO2 growth rate coupling
束熱帶水-年際二氧化碳日益增加的富增長率耦合
▲ 作者：Laibao Liu, Philippe Ciais, Mengxi Wu, Ryan S. Padrón, Pierre Friedlingstein, Jonas Schwaab, Lukas Gudmundsson & Sonia I. Seneviratne
▲ 鏈接：
https://www.nature.com/articles/s41586-023-06056-x
▲ 摘要：
過去60年，陸地生態系統已經吸收了約32%的人為二氧化碳（CO2）排放總量。然而，陸地碳-氣候反饋的巨大不確定性使得預測陸地碳匯如何響應未來的氣候變化變得困難。
熱帶地區大氣CO2增長率（CGR）的年際變化主要由陸地-大氣碳通量主導，這為探索陸地-氣候相互作用提供了機會。
科學家認為CGR的變化在很大程度上受溫度控制，但也有證據表明，水的可用性和CGR11之間存在緊密耦合。研究者利用全球大氣CO2記錄、陸地儲水量和降水數據，研究了氣候變化下熱帶陸地氣候條件與CGR的年際關系變化。
他們發現，與1960-1989年相比，1989-2018年熱帶水資源可得性與CGR的年際關系變得越來越負。這可能與厄爾尼諾/南方濤動遙相關變化驅動的熱帶水可用性異常的時空變化有關，包括空間補償性水效應的減弱。
研究還證明，大多數最先進的地球系統和陸地表面耦合模型不能再現水-碳耦合的加劇。研究結果表明，熱帶水分可得性正日益控制著陸地碳循環的年際變化，并調節著熱帶陸地碳-氣候反饋。
▲ 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調制
▲ 作者：Ryley G. Hill, Matthew Weingarten, Thomas K. Rockwell & Yuri Fialko
▲ 鏈接：
https://www.nature.com/articles/s41586-023-06058-9
▲ 摘要：
水文荷載可以刺激地殼的地震活動性。然而，引發大地震的證據仍然難以捉摸。南加州的南圣安德烈亞斯斷層（SSAF）毗鄰薩爾頓海，這是古卡韋拉湖的遺跡，在過去一千年里，它周期性地充滿并干涸。
本文利用新的地質和古地震資料證明，過去6次大地震可能發生在卡韋拉湖的高點。為了研究可能的因果關系，研究者計算了湖泊水位變化引起的庫侖應力隨時間的變化。
利用黏彈性地幔上的孔彈性地殼的完全耦合模型，研究者發現水文荷載使SSAF上的庫侖應力增加了幾百千帕斯卡，斷層應力率增加了2倍以上，這可能足以引發地震。
非垂直斷層傾角、斷層破壞帶的存在和側向孔隙壓力擴散增強了湖泊淹沒的不穩定效應。我們的模型可能適用于其他地區的水文負荷，無論是自然的還是人為的，都與大量的地震活動有關。
▲ 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.