2000年自然杂志（自然20220106出版一周论文导读）

编译｜冯维维

Nature, 6 January 2022, Volume 601 Issue 7891

《自然》2022年1月6日，第601卷，7891期

天体物理学Astrophysics

An early transition to magnetic supercriticality in star formation

磁流导致恒星形成

▲ 作者：T.-C. Ching, D. Li, C. Heiles, Z.-Y. Li, L. Qian, Y. L. Yue, J. Tang & S. H. Jiao

▲ 链接：

https://www.nature.com/articles/s41586-021-04159-x

▲ 摘要

磁场是星际介质和恒星制造过程中必不可少的一部分，但它仍然是一个“秘密”。太空中磁场的秘密可以归因于人们缺乏实验性的探测。

中国科学院国家天文台领导的国际合作团队研究表明，在星前核L1544内部探测到的磁场减弱，可能会改变人们对恒星形成的认识。探测结果表明，磁场变化——对星际介质的演化以及恒星形成十分重要——的出现时间可能比之前认为的更早。

星前核是一种会形成恒星的致密分子云。磁流相对质量的减弱被认为是恒星形成的必要条件。一些理论假设这种磁流变化发生在星前核仍十分致密的时期，这会引发星前核坍缩，导致大量恒星形成。不过，分析典型星前系统的星际场强一直颇有难度。

作者报道了他们在L1544恒星形成核外部冷原子气体中探测到的磁场，这个恒星形成核是一种介于无星与原恒星之间早期过渡阶段的无星分子云。他们发现，相比L1544周围的寒冷、中性原子云，这个恒星形成核周围的原子包层相对质量的磁场要弱13倍。作者指出，这一观测表明，磁流相对质量减弱——恒星形成的必要条件——的出现时间比经典理论预测的更早。

▲ Abstract

Magnetic fields have an important role in the evolution of interstellar medium and star formation. As the only direct probe of interstellar field strength, credible Zeeman measurements remain sparse owing to the lack of suitable Zeeman probes, particularly for cold, molecular gas. Here we report the detection of a magnetic field of 3.8 ± 0.3 microgauss through the H I narrow self-absorption (HINSA) towards L1544—a well-studied prototypical prestellar core in an early transition between starless and protostellar phases characterized by a high central number density and a low central temperature. A combined analysis of the Zeeman measurements of quasar H I absorption, H I emission, OH emission and HINSA reveals a coherent magnetic field from the atomic cold neutral medium (CNM) to the molecular envelope. The molecular envelope traced by the HINSA is found to be magnetically supercritical, with a field strength comparable to that of the surrounding diffuse, magnetically subcritical CNM despite a large increase in density. The reduction of the magnetic flux relative to the mass, which is necessary for star formation, thus seems to have already happened during the transition from the diffuse CNM to the molecular gas traced by the HINSA. This is earlier than envisioned in the classical picture where magnetically supercritical cores capable of collapsing into stars form out of magnetically subcritical envelopes.

A stellar stream remnant of a globular cluster below the metallicity floor

球状星团金属丰度下限的恒星流残留物

▲ 作者：Nicolas F. Martin, Kim A. Venn, Alessio Mucciarelli, etc.

▲ 链接：

https://www.nature.com/articles/s41586-021-04162-2

▲ 摘要

恒星喷出物逐渐丰富了形成恒星的气体，使化学丰度最低的恒星系统成为早期宇宙结构的直接化石。在银河系中，已知金属含量低于太阳铁含量千分之一的恒星有几百颗，但它们都不在球状星团中，球状星团是一些已知的最古老的恒星结构。这表明它们的金属含量至少约为太阳金属丰度的0.2%。

作者报道了观测到的C-19恒星流，其金属丰度小于太阳金属丰度的0.05%。C-19恒星的低金属度弥散和化学丰度表明，它是迄今发现的最缺乏金属的球状星团的潮汐残留物，明显低于过去认为的金属丰度下限：金属含量比现在观测到的要低得多的星团曾存在过，并将其恒星贡献给了银河系的光晕。

▲ Abstract

Stellar ejecta gradually enrich the gas out of which subsequent stars form, making the least chemically enriched stellar systems direct fossils of structures formed in the early Universe. Although a few hundred stars with metal content below 1,000th of the solar iron content are known in the Galaxy, none of them inhabit globular clusters, some of the oldest known stellar structures. These show metal content of at least approximately 0.2% of the solar metallicity. Here we report observations of a stellar stream, C-19, whose metallicity is less than 0.05% of the solar metallicity. The low metallicity dispersion and the chemical abundances of the C-19 stars show that this stream is the tidal remnant of the most metal-poor globular cluster ever discovered, and is significantly below the purported metallicity floor: clusters with significantly lower metallicities than observed today existed in the past and contributed their stars to the Milky Way halo.

粒子物理Particle Physics

A 16-parts-per-trillion measurement of the antiproton-to-proton charge–mass ratio

反质子与质子电荷质量比

▲ 作者：M. J. Borchert, J. A. Devlin, S. R. Erlewein, M. Fleck, S. Ulmer, etc.

▲ 链接：

https://www.nature.com/articles/s41586-021-04203-w

▲ 摘要

粒子物理学的标准模型既令人难以置信地成功，又明显地不完整。这些悬而未决的问题之一是可观测宇宙中物质和反物质惊人的不平衡，这激发了比较物质/反物质共轭的基本性质的高精确度实验。

作者在实验中直接研究质子和反质子的基本性质，在先进的低温潘宁阱系统中进行光谱分析。例如，他们曾比较了质子/反质子的磁矩，其精度比率为十亿分之1.5，比以前最好的测量结果提高了3000倍以上。作者报告了质子/反质子电荷质量比的新比较，其比率为万亿分之16。该结果是基于四项独立的长期研究的结合，记录了总共1.5年的时间跨度。

▲ Abstract

The standard model of particle physics is both incredibly successful and glaringly incomplete. Among the questions left open is the striking imbalance of matter and antimatter in the observable universe, which inspires experiments to compare the fundamental properties of matter/antimatter conjugates with high precision. Our experiments deal with direct investigations of the fundamental properties of protons and antiprotons, performing spectroscopy in advanced cryogenic Penning trap systems. For instance, we previously compared the proton/antiproton magnetic moments with 1.5 parts per billion fractional precision, which improved upon previous best measurements by a factor of greater than 3,000. Here we report on a new comparison of the proton/antiproton charge-to-mass ratios with a fractional uncertainty of 16 parts per trillion. Our result is based on the combination of four independent long-term studies, recorded in a total time span of 1.5 years.

Crystallization of bosonic quantum Hall states in a rotating quantum gas

旋转量子气体中玻色子量子霍尔态的结晶

▲ 作者：Biswaroop Mukherjee, Airlia Shaffer, Parth B. Patel, Zhenjie Yan, Cedric C. Wilson, Valentin Crépel, Richard J. Fletcher & Martin Zwierlein

▲ 链接：

https://www.nature.com/articles/s41586-021-04170-2

▲ 摘要

从分数阶量子霍尔液体到光学晶格中的原子，再到扭曲的双层石墨烯，相互作用对动能的支配地位是强相关量子物质的核心。作者研究了在最低朗道能级和接近最低朗道能级的朗道规范玻色-爱因斯坦凝聚体的纯相互作用驱动动力学。

作者观察到由磁旋子的凝结驱动的自发结晶现象，在磁极长度可见密度调制的励磁。云密度的增加平稳地将这种行为与量子版的开尔文-亥姆霍兹流体力学不稳定性联系起来，这种不稳定性是由快速旋转的冷凝物的剪切内部流动轮廓驱动的。在很长一段时间里，冷凝物自组织成一个由涡旋街分离的持续的液滴阵列，这些液滴通过相互作用和有效磁力的平衡稳定下来。

▲ Abstract

The dominance of interactions over kinetic energy lies at the heart of strongly correlated quantum matter, from fractional quantum Hall liquids, to atoms in optical lattices and twisted bilayer graphene. Here we study the purely interaction-driven dynamics of a Landau gauge Bose–Einstein condensate in and near the lowest Landau level. We observe a spontaneous crystallization driven by condensation of magneto-rotons, excitations visible as density modulations at the magnetic length. Increasing the cloud density smoothly connects this behaviour to a quantum version of the Kelvin–Helmholtz hydrodynamic instability, driven by the sheared internal flow profile of the rapidly rotating condensate. At long times the condensate self-organizes into a persistent array of droplets separated by vortex streets, which are stabilized by a balance of interactions and effective magnetic forces.

能源与生态Energy & Ecology

Drop-in fuels from sunlight and air

来自阳光和空气的运输燃料

▲ 作者：Remo Schäppi, David Rutz, Fabian Dähler, Alexander Muroyama, Philipp Haueter, Johan Lilliestam, Anthony Patt, Philipp Furler & Aldo Steinfeld

▲ 链接：

https://www.nature.com/articles/s41586-021-04174-y

▲ 摘要

目前，航空航运业二氧化碳排放约占人为排放总量的8%，旅游业和全球贸易的增长预计将进一步增加这一贡献。利用可充电电池驱动的电动机实现碳中和运输具有可行性，但对于长途商业旅行，特别是航空旅行来说，这种方式即便可能，也存在挑战。一种很有前途的解决方案是采用太阳能驱动的工艺从水和二氧化碳中提炼出的纯燃料。

作者利用一个模块化的5千瓦热试验太阳能系统，展示了整个热化学太阳能燃料生产链的操作，包括直接从环境空气中捕获H2O和CO2直接合成运输燃料（如甲醇和煤油）。他们接下来将进一步确定研究和开发工作，讨论将这些太阳能燃料推向市场所需的经济可行性和政策。

▲ Abstract

Aviation and shipping currently contribute approximately 8% of total anthropogenic CO2 emissions, with growth in tourism and global trade projected to increase this contribution further. Carbon-neutral transportation is feasible with electric motors powered by rechargeable batteries, but is challenging, if not impossible, for long-haul commercial travel, particularly air travel. A promising solution are drop-in fuels made from H2O and CO2 by solar-driven processes. Here we demonstrate the operation of the entire thermochemical solar fuel production chain, from H2O and CO2 captured directly from ambient air to the synthesis of drop-in transportation fuels, with a modular 5 kWthermal pilot-scale solar system operated under field conditions. We further identify the research and development efforts and discuss the economic viability and policies required to bring these solar fuels to market.

Experimental evidence for recovery of mercury-contaminated fish populations

汞污染鱼类种群恢复的实验证据

▲ 作者：Paul J. Blanchfield, John W. M. Rudd, Lee E. Hrenchuk, etc.

▲ 链接：

https://www.nature.com/articles/s41586-021-04222-7

▲ 摘要

汞（Hg）的人为释放是一个人类健康问题，因为强效毒物甲基汞（MeHg）主要由水生生态系统中无机汞的微生物甲基化形成，在人类食用的鱼类中积累到高浓度。作者进行了一项为期15年的全生态系统、单因素实验，以确定在一个北方湖泊及其流域汞添加量减少后鱼类甲基汞浓度下降的幅度和时间。

研究表明，尽管来自流域的汞含量可能不会随着沉积速率的降低而下降，但这项实验清楚地表明，任何湖泊汞含量的减少，无论是直接沉积还是径流携带，都将对鱼类消费者产生直接的好处。

▲ Abstract

Anthropogenic releases of mercury (Hg) are a human health issue because the potent toxicant methylmercury (MeHg), formed primarily by microbial methylation of inorganic Hg in aquatic ecosystems, bioaccumulates to high concentrations in fish consumed by humans. Here we conducted a 15-year whole-ecosystem, single-factor experiment to determine the magnitude and timing of reductions in fish MeHg concentrations following reductions in Hg additions to a boreal lake and its watershed. Although Hg loading from watersheds may not decline in step with lowering deposition rates, this experiment clearly demonstrates that any reduction in Hg loadings to lakes, whether from direct deposition or runoff, will have immediate benefits to fish consumers.

,