There exists a number of astronomical spectral phenomena that have remained unidentified after decades of extensive observations. The diffuse interstellar bands, the 220 nm feature, unidentified infrared emission bands, extended red emissions, and 21 and 30 μm emission features are seen in a wide variety of astrophysical environments. The strengths of these features suggest that they originate from chemical compounds made of common elements, possibly organic in nature. The quest to understand how such organic materials are synthesized and distributed across the Galaxy represents a major challenge to our understanding of the chemical content of the Universe.

中文翻译：

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星际介质中无法解释的光谱现象：介绍

经过数十年的广泛观察，存在许多天文光谱现象仍未被识别。在各种各样的天体物理环境中都可以看到漫射星际带、220 nm 特征、未识别的红外发射带、扩展的红色发射以及 21 和 30 μm 发射特征。这些特征的优势表明它们源自由普通元素组成的化合物，可能是有机的。探索这些有机材料是如何合成和分布在银河系中的，是对我们理解宇宙化学成分的重大挑战。