21-cm line
Definition
The 21-cm line is a spectral line emitted by neutral hydrogen atoms due to the hyperfine transition. It is a crucial tool in radio astronomy for mapping interstellar gas and studying galactic structures.
5 Must Know Facts For Your Next Test
- The 21-cm line results from the transition between two energy states of neutral hydrogen atoms.
- It has a wavelength of 21 centimeters, corresponding to a frequency of approximately 1420 MHz.
- This spectral line can penetrate interstellar dust, allowing astronomers to observe regions that are obscured in visible light.
- The 21-cm line is used to measure the distribution and density of neutral hydrogen in our galaxy and others.
- It plays a key role in understanding the spiral structure of galaxies by tracing the location and movement of hydrogen clouds.
Review Questions
- What causes the emission of the 21-cm line in neutral hydrogen atoms?
- Why is the 21-cm line particularly useful for mapping interstellar gas?
- How does the ability of the 21-cm line to penetrate dust benefit astronomers?
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Related terms
Hyperfine Transition: The change between two closely spaced energy levels within an atom's ground state, responsible for phenomena like the 21-cm line.
Neutral Hydrogen (HI): The most abundant form of hydrogen in space, consisting of one proton and one electron.
Radio Astronomy: The study of celestial objects using radio waves rather than visible light, crucial for observing phenomena like the 21-cm line.
