Polycyclic aromatic hydrocarbons (PAHs) have long been invoked in the study of interstellar and protostellar sources, but the unambiguous identification of any individual PAH has proven elusive until very recently. As a result, the formation mechanisms for this important class of molecules remain poorly constrained. Here we report the first interstellar detection of a pure hydrocarbon PAH, indene (C₉H₈), as part of the GBT Observations of TMC-1: Hunting for Aromatic Molecules (GOTHAM) survey. This detection provides a new avenue for chemical inquiry, complementing the existing detections of CN-functionalized aromatic molecules. From fitting the GOTHAM observations, indene is found to be the most abundant organic ring detected in TMC-1 to date. And from astrochemical modeling with nautilus, the observed abundance is greater than the model’s prediction by several orders of magnitude, suggesting that current formation pathways in astrochemical models are incomplete. The detection of indene in relatively high abundance implies related species such as cyanoindene, cyclopentadiene, toluene, and styrene may be detectable in dark clouds.

多环芳烃 (PAH) 长期以来一直被用于星际和原恒星来源的研究中，但直到最近才证明对任何单个 PAH 的明确识别是难以捉摸的。因此，这类重要分子的形成机制仍然受到很大限制。在这里，我们报告了首次星际探测到纯烃类多环芳烃茚 (C ₉ H ₈ )，作为 TMC-1 的 GBT 观测：寻找芳香分子 (GOTHAM) 调查的一部分。这种检测为化学探究提供了新的途径，补充了对 CN 功能化芳香分子的现有检测。通过拟合 GOTHAM 观测，发现茚是迄今为止在 TMC-1 中检测到的最丰富的有机环。并从天体化学建模nautilus，观测到的丰度比模型的预测高几个数量级，表明当前天体化学模型中的形成途径是不完整的。检测到相对高丰度的茚意味着可以在乌云中检测到相关物种，如氰基茚、环戊二烯、甲苯和苯乙烯。