Interstellar Matter
Table 1 shows a breakdown of the properties of the components of the ISM of the Milky Way.
| Component | Fractional Volume |
Scale Height (pc) |
Temperature (K) |
Density (atoms/cm³) |
State of hydrogen | Primary observational techniques |
|---|---|---|---|---|---|---|
| Molecular clouds | < 1% | 80 | 10—20 | 102—106 | molecular | Radio and infrared molecular emission and absorption lines |
| Cold Neutral Medium (CNM) | 1—5% | 100—300 | 50—100 | 20—50 | neutral atomic | H I 21 cm line absorption |
| Warm Neutral Medium (WNM) | 10—20% | 300—400 | 6000—10000 | 0.2—0.5 | neutral atomic | H I 21 cm line emission |
| Warm Ionized Medium (WIM) | 20—50% | 1000 | 8000 | 0.2—0.5 | ionized | Hα emission and pulsar dispersion |
| H II regions | < 1% | 70 | 8000 | 102—104 | ionized | Hα emission and pulsar dispersion |
| Coronal gas Hot Ionized Medium (HIM) |
30—70% | 1000—3000 | 106—107 | 10−4—10−2 | ionized (metals also highly ionized) |
X-ray emission; absorption lines of highly ionized metals, primarily in the ultraviolet |
Read more about this topic: Interstellar Medium
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