天文学家为什么对中性氢的 21 厘米谱线情有独钟？
Why do astronomers prize the 21-cm line of neutral hydrogen?
中性氢原子超精细结构跃迁发出 21 厘米射电，能穿透尘埃、示踪星系中的氢气分布与运动，是研究星系结构和宇宙再电离的关键探针。
The hyperfine transition of neutral hydrogen emits 21-cm radio that pierces dust and traces gas distribution and motion in galaxies, a key probe of galactic structure and cosmic reionization.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
Zeilik,《Astronomy: The Evolving Universe》第9版,Cambridge University Press,2002
M. Zeilik, Astronomy: The Evolving Universe, 9th ed., Cambridge University Press, 2002
#射电 #中性氢 #星系
21厘米氢线为什么能在射电天文里探测到比光学波段暗得多的中性氢云？
Why does the 21 cm hydrogen line let radio astronomers trace neutral hydrogen clouds that are far too faint to see optically?
银河系富含尘埃，可见光会被吸收散射，几万光年外的中性氢云在光学波段基本不可见。中性氢原子基态超精细能级之间的自发跃迁产生1420 MHz谱线，虽然单个跃迁概率极低（约一千万年一次），但星际氢柱体巨大且该波段可穿透尘埃。此外氢是宇宙中最丰富的元素，大量原子的累积辐射使这条线成为绘制银河系内外中性氢分布的主力手段。
Interstellar dust extinguishes visible light, so neutral hydrogen clouds across the Milky Way are essentially invisible optically. The ground-state hyperfine transition of atomic hydrogen emits at 1420 MHz; the spontaneous transition probability per atom is tiny (once per ~10 million years), but Galactic hydrogen columns are enormous and radio emission passes through dust unattenuated. Because hydrogen dominates the baryonic universe, the accumulated line emission maps neutral hydrogen throughout and beyond the Galaxy with high sensitivity.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-04
来源 · Source
Ewen & Purcell,《Observation of a Line in the Galactic Radio Spectrum: Radiation from Galactic Hydrogen at 1,420 Mc./sec.》,Nature,1951 (DOI: 10.1038/168356a0)；van de Hulst 1945年理论预言论文
Ewen & Purcell, 'Observation of a Line in the Galactic Radio Spectrum: Radiation from Galactic Hydrogen at 1,420 Mc./sec.', Nature, 1951, DOI: 10.1038/168356a0; van de Hulst prediction paper (1945)
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1038/168356a0
#21厘米线 #中性氢
中性氢的21厘米谱线为何能够穿透尘埃、勾勒出银河系旋臂的骨架?
Why can the 21 cm line of neutral hydrogen pierce interstellar dust and trace the skeleton of the Milky Way's spiral arms?
这条谱线来自氢原子基态的超精细结构跃迁,自发跃迁概率极低,但银河系中性氢的总质量巨大,足以产生明亮的可观测发射。21厘米处于射电波段,几乎不受尘埃消光影响,因而能看到光学手段无法触及的银道面远端。把谱线的多普勒位移代入银河系旋转曲线即可换算出距离,从而绘出旋臂的气体分布图。
The line originates in the hyperfine transition of the hydrogen ground state; its spontaneous rate is minuscule, yet the sheer mass of Galactic neutral hydrogen makes the emission bright. At 21 cm it sits in the radio band, so it suffers almost no dust extinction and reveals the far side of the Galactic plane that optical light cannot reach. Feeding the measured Doppler shifts into the Galactic rotation curve converts them into distances, mapping out the gas distribution along the arms.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Ewen 与 Purcell,1951年,Nature,168卷356页:银河系1420兆赫中性氢辐射的首次探测
Ewen & Purcell 1951, Nature, 168, 356 - Observation of a line in the galactic radio spectrum at 1420 MHz
独立核验依据 · Independent verification: 核验依据 1 CROSSREF 标识 10.1038/168356a0：Observation of a Line in th
#中性氢21厘米谱线 #银河系旋臂