14Diamonds in the Sky

Ever wondered where to look for nanodiamonds (NDs) in nature? Perhaps a more relevant question is: Do they even exist in natural environment? After all, NDs are very tiny and could be exceedingly difficult to find. For example, in order to make up a thickness of a single‐strand human hair, one would need to weave 1000 NDs side‐by‐side, let alone produce a size of a half‐carat diamond (as on a humble wedding ring) that would need a mound of 30 trillion (3 × 1013) NDs. While diamonds appear to be extremely rare on the earth surface (Section 2.3), who would have ever thought that in dark skies over the far deep space, there just might be abundant NDs present on stars and nebulas enough to light up the skies throughout an entire galaxy? How did scientists find it? This is the story of unidentified infrared (UIR) emission and extended red emission (ERE) of stardust [1].

14.1 Unidentified Infrared Emission

Carbon is the fourth most abundant element in the Galaxy. The possible presence of this element as diamond in space was first proposed by Saslaw and Gaustad [2] in 1969 to account for the observed interstellar extinction curves in the far ultraviolet (UV) region of galactic radiation. Little, if any, attention was paid to this hypothesis until 1987 when Lewis et al. [3] reported the discovery of small diamond grains in primitive meteorites from outside of the solar system (Section 2.4). These diamond grains have an average size of approximately 3 nm in diameter ...

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