 In addition to his work on planetary nebulae, Kwok was also recognized for his discovery of proto-planetary nebulae, the missing link in our understanding of the late stages of stellar evolution, and the discovery of the unidentified emission feature at 21 micrometres which is believed to be an unusual carbonaceous compound .Using space-based infrared telescopes, he has found that organic compounds with aromatic and aliphatic structures can be synthesized rapidly in the late stages of stellar evolution.These star-manufactured compounds are now known to have spread widely throughout the Galaxy, and are believed to have played a role in the chemical enrichment of the early solar system.