Hydrogen in the Milky Way

Hydrogen in the Milky Way PowerPoint PPT Presentation


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Hydrogen in the Milky Way

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1. 1 Hydrogen in the Milky Way Hydrogen is the most abundant element in our galaxy. The 21-cm Line Students need knowledge of the basic structure of the atom: protons, electrons.Students need knowledge of the basic structure of the atom: protons, electrons.

2. 2 Electronic Energy Levels Atoms emit a photon of light at a specific wavelength when an electron falls to a lower energy level. The 21-cm Line Basic properties of waves: frequency, wavelength.Basic properties of waves: frequency, wavelength.

3. 3 The resulting dark line spectrum identifies hydrogen. Hydrogen is detected using a technique called spectroscopy. The 21-cm Line

4. 4 An Element’s Signature The 21-cm Line

5. 5 Hydrogen only has only one electron spinning around its nucleus. How can just a spinning electron have energy levels? The 21-cm Line

6. 6 The electron spin energy of a hydrogen atom is slightly different depending on whether the spins of the proton and electron are in the same direction or opposite directions. YES!

7. 7 The 21-cm Line If the spin of the electron changes from the higher energy level to the lower energy one, a photon with a wavelength of 21 cm is emitted. The 21-cm Line

8. 8 A 21-cm Hydrogen Spectrum

9. 9 Spectral Lines and Motion Spectral lines can tell us whether the source is stationary or moving. If the source is moving, the spectral line will be shifted (called a Doppler shift). The 21-cm Line

10. 10 The spectrum line shift tells us the motion of a source (stars, galaxies, gases, etc.). The 21-cm Line

11. 11 Shift in wavelength If the source is moving toward the observer, the spectral line will be shifted to a shorter wavelength. If the source is moving away from the observer, the spectral line will be shifted to a longer wavelength. The 21-cm Line

12. 12 Wavelength and velocity The relative change in wavelength is related to the source’s velocity.

13. 13 Uses of the 21-cm line The Milky Way has over 3 billion solar masses of hydrogen gas. Enough hydrogen atoms so that the 21-cm line is easily detected by radio telescopes. Therefore, it is the best way to map the structure of the galaxy.

14. 14 Example: Rotation of the Milky Way

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