中性氢的 21 厘米谱线是怎样产生的?它在研究星际介质时有什么独特优势?
How is the 21-centimeter line of neutral hydrogen produced, and what unique advantage does it offer for studying the interstellar medium?
它来自氢原子基态的超精细跃迁:电子与质子自旋由平行翻转为反平行时,会释放1420兆赫兹的射电光子。星际尘埃强烈吸收可见光,射电波却几乎畅行无阻,而中性氢又是星际介质的主要组分,所以这条谱线能穿透整个银河系,用来绘制氢气分布并测定星系自转曲线,1951年由Ewen与Purcell首次探测成功。
It arises from the hyperfine transition of the ground-state hydrogen atom: when the electron and proton spins flip from parallel to antiparallel alignment, a 1420 MHz radio photon is released. Interstellar dust strongly absorbs visible light while radio waves pass almost freely, and neutral hydrogen dominates the interstellar gas, so this line penetrates the entire galaxy, tracing hydrogen maps and galactic rotation curves; Ewen and Purcell first detected it in 1951.
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CC BY 4.0 · 已核验 · Verified 2026-11-03
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Draine 所著 Physics of the Interstellar and Intergalactic Medium,Princeton University Press,2011年;Ewen 与 Purcell,1951年,Nature,168卷356页
B.T. Draine, Physics of the Interstellar and Intergalactic Medium, Princeton University Press 2011; Ewen & Purcell 1951, Nature, 168, 356 - First detection of the galactic 21-cm line
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#星际介质 #21厘米线 #中性氢
星际介质通常划分为哪几个温度相差悬殊的相?其中热相气体主要由什么机制加热?
Into which widely different temperature phases is the interstellar medium usually divided, and what mechanism mainly heats its hot phase?
通常分为四相:冷分子云约10至20K、冷原子气体约100K、暖气体约8000K、热电离气体达百万K量级。McKee与Ostriker的三相模型指出,超新星激波扫过星际空间时把低密度气体冲击加热到百万开尔文,形成充满热相的空腔;随后辐射冷却使部分气体重新凝聚为冷云,各相近似处于压力平衡中共存。
Conventionally four phases: cold molecular clouds near 10 to 20 K, cold atomic gas around 100 K, warm gas near 8000 K, and hot ionized gas of order a million kelvin. In the three-phase picture of McKee and Ostriker, supernova blast waves shock-heat tenuous gas to about a million kelvin, filling low-density cavities, while radiative cooling lets part of the gas condense back into cold clouds, the phases coexisting near pressure equilibrium.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-04
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McKee, Ostriker,《A theory of the interstellar medium - Three components regulated by supernova explosions in an inhomogeneous substrate》,The Astrophysical Journal,1977 (DOI: 10.1086/155667)
McKee, Ostriker, 'A theory of the interstellar medium - Three components regulated by supernova explosions in an inhomogeneous substrate', The Astrophysical Journal, 1977, DOI: 10.1086/155667
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1086/155667
#星际介质 #多相结构 #超新星激波
巨分子云为何被称作恒星的育婴房?它们又靠什么避免立刻整体坍缩?
Why are giant molecular clouds called stellar nurseries, and what keeps them from collapsing wholesale right away?
因为氢分子只能在尘埃遮蔽紫外线、低温高密的环境里大量存活,这类云正是新恒星集中诞生之处,猎户座星云便是近旁实例。巨分子云的质量远超金斯质量,本应整体快速坍缩,实际上却由湍流运动、磁场与热压力共同支撑,维持数百万年的准稳态;湍流又把云碎裂成众多致密核,各核分别坍缩成星团,所以恒星往往成批出生。
Molecular hydrogen survives in bulk only where dust screens out ultraviolet light inside cold, dense clouds, and such clouds are exactly where new stars gather to be born, the Orion nebula being a nearby case. Although far more massive than their Jeans mass and thus prone to rapid global collapse, giant molecular clouds are propped up by turbulent motions, magnetic fields and thermal pressure in a quasi-steady state lasting millions of years, while turbulence fragments them into dense cores that collapse separately into clusters, which is why stars tend to form in batches.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-04
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Shu、Adams 与 Lizano,《Star Formation in Molecular Clouds: Observation and Theory》,Annual Review of Astronomy and Astrophysics,1987 (DOI: 10.1146/annurev.aa.25.090187.000323)
Shu, Adams & Lizano, 'Star Formation in Molecular Clouds: Observation and Theory', Annual Review of Astronomy and Astrophysics, 1987, DOI: 10.1146/annurev.aa.25.090187.000323
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1146/annurev.aa.25.090187.000323
#巨分子云 #恒星形成 #金斯质量
为什么星光穿过星际空间会变暗又变红,天文学家又该如何改正这种效应?
Why does starlight grow dimmer and redder while crossing interstellar space, and how can astronomers correct for this effect?
这是星际尘埃的消光与红化:尘埃吸收并散射星光使恒星变暗,而散射效率随波长变短而增强,蓝光比红光损失更多,恒星颜色因而偏红。改正时先用同谱型的近距恒星作参照或用红外测光估计色余E(B-V),再依消光曲线逐波段扣除损失;由于长波段几乎不受影响,红外与射电是窥探尘埃背后的首选窗口。
This is the extinction and reddening caused by interstellar dust: grains absorb and scatter starlight, dimming stars, and scatter short wavelengths more efficiently than long ones, so blue light is lost more than red and stars appear too red. To correct, astronomers estimate the color excess E(B-V) using nearby reference stars of the same spectral type or infrared photometry, then remove the per-band losses along an extinction curve; since long wavelengths slip through almost untouched, infrared and radio windows are the favored ways to peer behind dust.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-02
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L. Spitzer 所著 Physical Processes in the Interstellar Medium,Wiley 出版社,1978年
Lyman Spitzer Jr., Physical Processes in the Interstellar Medium, Wiley, 1978
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#星际尘埃 #星际消光 #星际红化
初生的原恒星为什么反而要喷出笔直高速的双极喷流?这对它们自己的成长有什么意义?
Why do newborn protostars launch narrow, high-speed bipolar jets, and what good do these jets do the growing star itself?
喷流是原恒星摆脱多余角动量的出口:坍缩气体携带分子云的自转向中心坠落,若不把这些角动量送走,物质就会转得过快而难以继续吸积。磁化星盘沿缠绕的磁力线把部分气体甩出,旋转又将其准直成狭窄的双极喷流,带走绝大部分角动量,外层物质才得以持续落向星盘与恒星;喷流还在母云中犁出空腔、注入湍流,反过来调节恒星形成的节奏。猎户座等恒星形成区里的 HH 天体链,正是喷流撞击周围气体的发光痕迹。
Jets are the outlet through which protostars shed surplus angular momentum: infalling gas carries the parent cloud's spin, and without an exit it would whirl too fast to keep accreting. A magnetized disk flings part of the gas along wound-up field lines, and rotation collimates it into twin narrow jets that ferry away most of the angular momentum, so outer material can keep settling onto disk and star. Carving cavities and injecting turbulence into the natal cloud, the jets also throttle further star formation; chains of Herbig-Haro objects in Orion and other star-forming regions glow wherever they slam into surrounding gas.
难度 入门 · 适合 大众
CC BY 4.0 · 来源待核验 · Source pending review
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出处备注：此条未指向带版次的可引用著作（通识性内容、机构文件或未展开的英文书名），本库不提供独立书目出处；如需精确引用，需由编辑补全具体篇目与版次。
A. Frank 等人,2014年,Annual Review of Astronomy and Astrophysics,52卷171页:从恒星到云的喷流与外流;J. Bally,2016年,Annual Review of Astronomy and Astrophysics,54卷491页:原恒星外流
A. Frank et al. 2014, Annual Review of Astronomy and Astrophysics, 52, 171 - Jets and outflows from star to cloud; J. Bally 2016, Annual Review of Astronomy and Astrophysics, 54, 491 - Protostellar outflows
#恒星形成区 #原恒星喷流 #HH天体
漂浮在星际空间的尘埃颗粒是从哪里来的?除了遮挡星光,它们还为银河系立过哪些功劳?
Where do the tiny dust grains drifting through interstellar space come from, and beyond blocking starlight, what services have they rendered the Galaxy?
这些微米级颗粒主要由碳、硅、镁、铁等耐熔元素凝结而成,大多诞生于渐近巨星支恒星的外层大气与超新星抛出的致密团块,进入星际空间后还会裹上冰幔继续长大。它们功劳不小:颗粒表面是氢原子两两结合成氢分子的主要催化车间;遮挡紫外辐射,替寒冷分子云保住低温;吸饱星光再以红外辐射释放,助星云散热坍缩成恒星。
These micron-scale grains condense chiefly from refractory elements such as carbon, silicon, magnesium and iron, most born in the outer atmospheres of asymptotic-giant-branch stars and in dense knots of supernova ejecta, later growing icy mantles in interstellar clouds. Their services are considerable: grain surfaces are the main workshop where hydrogen atoms pair off into molecular hydrogen; they block ultraviolet photons, keeping cold molecular clouds frigid; having swallowed starlight they reradiate it in the infrared, helping nebulae shed heat and collapse into stars.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
B. T. Draine,2011年,书 Physics of the Interstellar and Intergalactic Medium,Princeton University Press;T. Henning,2010年,Annual Review of Astronomy and Astrophysics,48卷21号:Cosmic Silicates
B. T. Draine 2011, Physics of the Interstellar and Intergalactic Medium, Princeton University Press; T. Henning 2010, Annual Review of Astronomy and Astrophysics, 48, 21 - Cosmic Silicates
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#星际尘埃 #氢分子形成 #恒星形成