韦伯窥视分子云的冰冻核心——揭示星前冰化学的阴暗面

一个国际天文学家小组报告说，在冷分子云的最黑暗区域发现了多种冰，但通过研究该区域进行了测量。 这一发现使天文学家能够检查将被纳入未来系外行星的简单、冰冷的粒子，同时为了解更复杂粒子的起源打开了一个新窗口，这些粒子是创造生命基石的第一步。 图片来源：图片：NASA、ESA、CSA，科学：Fengwu Sun（Steward 天文台）、Zak Smith（开放大学）、IceAge ERS ​​团队，图像处理：M. Zamani (ESA/Webb)

韦伯确定了多种分子的固定形式，包括二氧化碳、氨和甲烷。

一个国际天文学家小组宣布使用[{” attribute=””>NASA’s James Webb Space Telescope. This result allows astronomers to examine the simple icy molecules that will be incorporated into future exoplanets, while opening a new window on the origin of more complex molecules that are the first step in the creation of the building blocks of life.

This image by NASA’s James Webb Space Telescope’s Near-Infrared Camera (NIRCam) features the central region of the Chamaeleon I dark molecular cloud, which resides 630 light years away. The cold, wispy cloud material (blue, center) is illuminated in the infrared by the glow of the young, outflowing protostar Ced 110 IRS 4 (orange, upper left). The light from numerous background stars, seen as orange dots behind the cloud, can be used to detect ices in the cloud, which absorb the starlight passing through them. Credit: Image: NASA, ESA, CSA, Science: Fengwu Sun (Steward Observatory), Zak Smith (The Open University), IceAge ERS Team, Image Processing: M. Zamani (ESA/Webb)

James Webb Space Telescope Unveils Dark Side of Pre-stellar Ice Chemistry

If you want to build a habitable planet, ices are a vital ingredient because they are the main source of several key elements — namely carbon, hydrogen, oxygen, nitrogen, and sulfur (referred to here as CHONS). These elements are important ingredients in both planetary atmospheres and molecules like sugars, alcohols, and simple amino acids.

An international team of astronomers using NASA’s James Webb Space Telescope has obtained an in-depth inventory of the deepest, coldest ices measured to date in a molecular cloud.^[1] 除了像水这样的简单冰，该团队还能够识别各种分子的冷冻形式，从硫化羰、氨和甲烷，到最简单的复杂有机分子甲醇。 （研究人员认为，当存在六个或更多原子时，有机分子会变得复杂。）这是迄今为止对可用于形成未来几代恒星和行星的冰成分（在年轻恒星形成过程中被加热之前）进行的最全面的普查。

荷兰莱顿天文台的天文学家 Melissa McClure 说，她是该观测计划的首席研究员，也是描述这一发现的论文的主要作者。 “这些观察为构成生命基石所需的简单和复杂分子的形成途径打开了一扇新窗口。”

上图的注释版本。 本研究中使用的两颗背景恒星 NIR38 和 J110621 在图像上以白色表示。 图片来源：NASA、ESA、CSA 和 M. Zamani (ESA/Webb)； 科学：F. Sun（斯图沃德天文台）、Z. Smith（开放大学）和 Ice Age ERS ​​团队

除了他们识别的分子外，该团队还发现了比甲醇更复杂的分子证据，尽管他们尚未明确将这些信号归因于特定分子，但这首次证明复杂分子在分子云的冰冷深处形成在星星诞生之前…

莱顿天文台的天文学家 Will Rocha 补充说，他为这一发现做出了贡献。 “这可能意味着行星系统中益生元前体分子的存在是恒星形成的常见结果，而不是我们太阳系的独特特征。”

通过检测含硫的冰状硫化羰，研究人员首次能够估算出冰状星前尘埃颗粒中硫的含量。 虽然测得的量比之前观察到的要多，但它仍然小于根据云的密度预计存在的总量。 其他 CHONS 也是如此。 天文学家面临的主要挑战是了解这些元素隐藏在哪里：在冰、烟灰状物质或岩石中。 每种材料中的 CHONS 数量决定了最终处理这些物品的数量[{” attribute=””>exoplanet atmospheres and how much in their interiors.

“The fact that we haven’t seen all of the CHONS that we expect may indicate that they are locked up in more rocky or sooty materials that we cannot measure,” explained McClure. “This could allow a greater diversity in the bulk composition of terrestrial planets.

Astronomers have taken an inventory of the most deeply embedded ices in a cold molecular cloud to date. They used light from a background star, named NIR38, to illuminate the dark cloud called Chamaeleon I. Ices within the cloud absorbed certain wavelengths of infrared light, leaving spectral fingerprints called absorption lines. These lines indicate which substances are present within the molecular cloud.
These graphs show spectral data from three of the James Webb Space Telescope’s instruments. In addition to simple ices like water, the science team was able to identify frozen forms of a wide range of molecules, from carbon dioxide, ammonia, and methane, to the simplest complex organic molecule, methanol.
In addition to the identified molecules, the team found evidence for molecules more complex than methanol (indicated in the lower-right panel). Although they didn’t definitively attribute these signals to specific molecules, this proves for the first time that complex molecules form in the icy depths of molecular clouds before stars are born.
The upper panels and lower-left panel all show the background star’s brightness versus wavelength. A lower brightness indicates absorption by ices and other materials in the molecular cloud. The lower-right panel displays the optical depth, which is essentially a logarithmic measure of how much light from the background star gets absorbed by the ices in the cloud. It is used to highlight weaker spectral features of less abundant varieties of ice.
Credit: Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI), Science: Klaus Pontoppidan (STScI), Nicolas M. Crouzet (LEI), Zak Smith (The Open University), Melissa McClure (Leiden Observatory)

Chemical characterization of the ices was accomplished by studying how starlight from beyond the molecular cloud was absorbed by icy molecules within the cloud at specific infrared wavelengths visible to Webb. This process leaves behind chemical fingerprints known as absorption lines which can be compared with laboratory data to identify which ices are present in the molecular cloud. In this study, the team targeted ices buried in a particularly cold, dense, and difficult-to-investigate region of the Chamaeleon I molecular cloud, a region roughly 500 light-years from Earth that is currently in the process of forming dozens of young stars.

“We simply couldn’t have observed these ices without Webb,” elaborated Klaus Pontoppidan, Webb project scientist at the Space Telescope Science Institute in Baltimore, Maryland, who was involved in this research. “The ices show up as dips against a continuum of background starlight. In regions that are this cold and dense, much of the light from the background star is blocked, and Webb’s exquisite sensitivity was necessary to detect the starlight and therefore identify the ices in the molecular cloud.”

这项研究是其中的一部分 冰河世纪项目，Webb 的 13 个早期发布程序之一。 这些观测旨在展示韦伯的观测能力，并让天文学界了解如何充分利用其仪器。 冰河时代团队已经计划进行更多观测，并希望追踪冰从形成到冰彗星聚集的整个过程。

“这只是一系列光谱快照中的第一次，我们将看到冰如何从它们的初始成分演变成原行星盘的彗星形成区域，”麦克卢尔总结道。 “这将告诉我们哪种冰混合物——以及哪些元素——最终可以被输送到类地系外行星的表面，或者融入气态巨行星或冰行星的大气层。”

这些结果发表在 1 月 23 日的 自然天文学.

笔记

1. 分子云是巨大的星际气体和尘埃云，其中可以形成氢和一氧化碳等分子。 如果分子云中密度高于周围环境的冷致密团块坍塌形成原恒星，则它们可能是恒星形成的场所。

参考资料：M.K. McClure, D. 的“冰河时代 JWST 致密分子云雪清单” . Qasim、MJ Rasheed、ZL Smith、Fengo Sun、Tracy L. Beck、ACA Bogert、W. Brown、P. Caselli、S.B. Charnley、Herma M. Cobbin、H. Dickinson、M.N. Drozdovskaya、Egami、J. Erkal、H. Fraser RT Garrod、DeHarsono、S. Iopoulou、I Jimenez-Serra、MJin、JK Jorgensen、Lee Christensen、DC Lees、MRS McCostra、Brett A McGuire、JG Melnick、Karen I Oberg、May Palumbo、T. Shimonishi、J.A. Storm、 EF Van Dishoek 和 H. Lennarts，2023 年 1 月 23 日，可在此处获取。 自然天文学.
DOI: 10.1038/s41550-022-01875-w

詹姆斯韦伯太空望远镜是世界上首屈一指的太空科学天文台。 韦伯将解开我们太阳系中的谜团，展望其他恒星周围的遥远世界，探索我们宇宙的神秘结构和起源以及我们在其中的位置。 Webb 是由 NASA 及其合作伙伴 ESA（欧洲航天局）和加拿大航天局牵头的一项国际计划。