The existence of interstellar molecules is recognized because, just like the hydrogen atom, they emit radio waves in the form of spectral lines. Today over 140 molecular species have been identified in interstellar space. This number compares with 27 in the 1973 edition of this book, and 64 in the 1987 edition. Another 500 or so lines have been observed but not identified. Most of these species are detected at very high frequencies, about 5,000 MHz (short wavelengths, below 6 cm and down to a fraction of a millimeter).
KeywordsStar Formation Radio Source Galactic Center Dust Cloud Tauri Star
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