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Nature, Volume 618 Issue 7966, 22 June 2023

(資料圖片)

《自然》第618卷，7966期，2023年6月22日

天體物理學(xué)和天體化學(xué)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(gè)宇宙歷史中，塵埃顆粒吸收了恒星發(fā)出的一半輻射，并以紅外波長(zhǎng)重新發(fā)射這些能量。多環(huán)芳烴（PAHs）是一種大型有機(jī)分子，可追蹤毫米大小的塵埃顆粒，并調(diào)節(jié)星系內(nèi)星際氣體的冷卻。由于以前的紅外望遠(yuǎn)鏡的靈敏度和波長(zhǎng)覆蓋范圍有限，在非常遙遠(yuǎn)的星系中觀測(cè)多環(huán)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(yuǎn)鏡在大爆炸后不到15億年觀測(cè)到的星系中探測(cè)到3.3 μm多環(huán)芳香烷特征的觀測(cè)結(jié)果。多環(huán)芳烴特征的高等效寬度表明，整個(gè)星系的紅外發(fā)射主要是恒星形成，而不是黑洞吸積。

多環(huán)芳烴分子、熱塵埃、大塵埃顆粒和恒星發(fā)出的光在空間上彼此不同，導(dǎo)致多環(huán)芳烴等效寬度和多環(huán)芳烴與整個(gè)星系的總紅外光度之比發(fā)生了數(shù)量級(jí)的變化。研究者觀察到的空間變化表明，多環(huán)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(chǎng)中存在較大差異。我們的觀察表明，多環(huán)芳烴分子和大塵埃顆粒的發(fā)射差異是早期星系局部過程的復(fù)雜結(jié)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(duì)不穩(wěn)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(zhì)量最大、壽命最短的恒星主導(dǎo)著前銀河系時(shí)代的化學(xué)演化。在數(shù)值模擬的基礎(chǔ)上，人們?cè)缇屯茰y(cè)這類第一代恒星的質(zhì)量可達(dá)數(shù)百個(gè)太陽質(zhì)量。

超大質(zhì)量的第一代恒星的質(zhì)量范圍在140到260太陽質(zhì)量之間，預(yù)計(jì)會(huì)通過對(duì)不穩(wěn)定超新星豐富早期星際介質(zhì)。然而，經(jīng)過幾十年的觀測(cè)努力，尚未能獨(dú)特識(shí)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(bào)告了一顆極低鈉和鈷豐度的金屬極貧恒星的化學(xué)成分。這顆恒星中鈉與鐵的比值比太陽低兩個(gè)數(shù)量級(jí)以上。這顆恒星的奇電荷數(shù)和偶電荷數(shù)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(yīng)，加上鈉和α元素的缺乏，與對(duì)質(zhì)量超過140個(gè)太陽質(zhì)量的恒星產(chǎn)生的原始對(duì)不穩(wěn)定超新星的預(yù)測(cè)相一致。這提供了一個(gè)清晰的化學(xué)特征，表明早期宇宙中存在非常大質(zhì)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(xué)Physics

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

具有光子介導(dǎo)相互作用的單一費(fèi)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(zhì)中一種基本的長(zhǎng)程秩序，與晶體結(jié)構(gòu)的自組織有關(guān)。DW階與超流動(dòng)性的相互作用會(huì)導(dǎo)致復(fù)雜的情況，這對(duì)理論分析提出了很大的挑戰(zhàn)。

過去幾十年，可調(diào)諧量子費(fèi)米氣體已經(jīng)成為探索強(qiáng)相互作用費(fèi)米子物理學(xué)的模型系統(tǒng)，包括最著名的磁有序、配對(duì)和超流動(dòng)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(qū)動(dòng)的高精細(xì)光學(xué)腔中實(shí)現(xiàn)了具有強(qiáng)的、可調(diào)諧的接觸相互作用和光子介導(dǎo)的、空間結(jié)構(gòu)的遠(yuǎn)程相互作用的費(fèi)米氣體。

在一個(gè)臨界的遠(yuǎn)程相互作用強(qiáng)度之上，DW階在系統(tǒng)中是穩(wěn)定的，研究者通過其超輻射光散射特性來識(shí)別。他們定量地測(cè)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(fā)生變化時(shí)DW階的開始變化，定性地與平均場(chǎng)理論一致。將遠(yuǎn)距相互作用的強(qiáng)度和符號(hào)調(diào)整到低于自排序閾值時(shí)，原子DW磁化率變化超過一個(gè)數(shù)量級(jí)，表明對(duì)接觸和遠(yuǎn)距相互作用的獨(dú)立和同時(shí)控制。研究者表示，該實(shí)驗(yàn)裝置為超流體與DW階序相互作用的實(shí)驗(yàn)研究提供了一個(gè)完全可調(diào)和微觀可控的平臺(tái)。

▲ 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(shí)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(shí)間傳輸和光時(shí)鐘的結(jié)合，為連接地面光時(shí)鐘和未來天基光時(shí)鐘的大規(guī)模自由空間網(wǎng)絡(luò)開辟了可能性。這樣的網(wǎng)絡(luò)有望更好地測(cè)試廣義相對(duì)論、暗物質(zhì)搜索和引力波探測(cè)。

將光學(xué)時(shí)鐘連接到遠(yuǎn)程衛(wèi)星的能力可以實(shí)現(xiàn)天基超長(zhǎng)基線干涉測(cè)量、先進(jìn)的衛(wèi)星導(dǎo)航、基于時(shí)鐘的大地測(cè)量以及洲際時(shí)間傳播的數(shù)千倍改進(jìn)。

到目前為止，只有光學(xué)時(shí)鐘朝著量子限制性能的方向發(fā)展。相比之下，光時(shí)間傳遞沒有在由接收光子數(shù)量設(shè)定的類似量子極限下運(yùn)行。研究者展示了時(shí)間傳輸與近量子限制的采集和定時(shí)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(fā)射功率低至40微瓦，遠(yuǎn)距離站點(diǎn)同步到320阿秒。這種近乎量子限制的操作對(duì)于光子少且放大成本高的長(zhǎng)距離自由空間鏈路至關(guān)重要：在4.0 mW的發(fā)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(shí)間傳輸?shù)降厍蛲杰壍馈?/p>

▲ 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(xué)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(zhǎng)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(tài)系統(tǒng)已經(jīng)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(yù)測(cè)陸地碳匯如何響應(yīng)未來的氣候變化變得困難。

熱帶地區(qū)大氣CO2增長(zhǎng)率（CGR）的年際變化主要由陸地-大氣碳通量主導(dǎo)，這為探索陸地-氣候相互作用提供了機(jī)會(huì)。

科學(xué)家認(rèn)為CGR的變化在很大程度上受溫度控制，但也有證據(jù)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(chǔ)水量和降水?dāng)?shù)據(jù)，研究了氣候變化下熱帶陸地氣候條件與CGR的年際關(guān)系變化。

他們發(fā)現(xiàn)，與1960-1989年相比，1989-2018年熱帶水資源可得性與CGR的年際關(guān)系變得越來越負(fù)。這可能與厄爾尼諾/南方濤動(dòng)遙相關(guān)變化驅(qū)動(dòng)的熱帶水可用性異常的時(shí)空變化有關(guān)，包括空間補(bǔ)償性水效應(yīng)的減弱。

研究還證明，大多數(shù)最先進(jìn)的地球系統(tǒng)和陸地表面耦合模型不能再現(xiàn)水-碳耦合的加劇。研究結(jié)果表明，熱帶水分可得性正日益控制著陸地碳循環(huán)的年際變化，并調(diào)節(jié)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(diào)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(dòng)性。然而，引發(fā)大地震的證據(jù)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(zhì)和古地震資料證明，過去6次大地震可能發(fā)生在卡韋拉湖的高點(diǎn)。為了研究可能的因果關(guān)系，研究者計(jì)算了湖泊水位變化引起的庫侖應(yīng)力隨時(shí)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(fā)現(xiàn)水文荷載使SSAF上的庫侖應(yīng)力增加了幾百千帕斯卡，斷層應(yīng)力率增加了2倍以上，這可能足以引發(fā)地震。

非垂直斷層傾角、斷層破壞帶的存在和側(cè)向孔隙壓力擴(kuò)散增強(qiáng)了湖泊淹沒的不穩(wěn)定效應(yīng)。我們的模型可能適用于其他地區(qū)的水文負(fù)荷，無論是自然的還是人為的，都與大量的地震活動(dòng)有關(guān)。

▲ 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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