"Long before it's in the papers"
October 27, 2011

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Surprisingly complex organic matter identified in space

Oct. 27, 2011
Courtesy of The University of Hong Kong
and World Science staff

Or­gan­ic mol­e­cules of un­ex­pected com­plex­ity—si­mi­lar to those that serve as the in­gre­di­ents of life—ex­ist through­out the uni­verse, a study has found.

The re­sults sug­gest com­plex or­gan­ic com­pounds can be made nat­u­rally by stars, and not just by liv­ing things, ac­cord­ing to re­search­ers, who re­port­ed their work in the Oct. 27 is­sue of the jour­nal Na­ture.

Sun Kwok and Yong Zhang of the Uni­vers­ity of Hong Kong found that an or­gan­ic mol­e­cule com­monly found through­out the uni­verse con­tains a mix­ture of ar­o­mat­ic, or ring-like, and al­i­phat­ic, or chain-like, parts. These chem­i­cal struc­tures re­sem­ble those of coal and pe­tro­le­um, the re­search­ers not­ed, types of or­gan­ic ma­te­ri­al pre­vi­ously thought to arise only from liv­ing or­gan­isms.

The re­search­ers were in­ves­ti­gat­ing an un­solved puz­zle: a set of in­fra­red light emis­sions de­tected in stars and ga­lax­ies. For over two dec­ades, it was widely thought that these “u­niden­ti­fied in­fra­red emis­sion fea­tures” come from sim­ple or­gan­ic mol­e­cules made of car­bon and hy­dro­gen atoms, called pol­y­cy­clic ar­o­mat­ic hydrocar­bons. 

But us­ing da­ta from the Eu­ro­pe­an Space Agen­cy’s In­fra­red Space Ob­serv­a­to­ry and NASA’s Spitzer Space Tel­e­scope, Kwok and Zhang con­clud­ed that the sub­stances gen­er­at­ing these emis­sions are much more com­plex. By an­a­lyz­ing the light of star dust formed in ex­plod­ing stars called no­vae, they found that stars are mak­ing these com­plex or­gan­ic com­pounds on ex­tremely short time scales of weeks, and throw­ing them off in­to space.

“The­o­retic­ally,” it’s “im­pos­si­ble” for stars to cre­ate these mol­e­cules, “but ob­serva­t­ionally we can see it hap­pen­ing,” Kwok said.

The or­gan­ic star dust is si­m­i­lar in struc­ture to com­plex or­gan­ic com­pounds found in me­te­orites, Kwok and Zhang added. Since me­te­orites are rem­nants of the early So­lar Sys­tem, the find­ings raise the pos­si­bil­ity that stars en­riched the early So­lar Sys­tem with or­gan­ic com­pounds. The early Earth was sub­jected to se­vere bom­bard­ments by comets and as­ter­oids, which might have car­ried or­gan­ic star dust, the re­search­ers spec­u­late.

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Organic compounds of unexpected complexity—the types of molecules used as the ingredients of life—exist throughout the Universe, a study has found. The results suggest complex organic compounds can be made naturally by stars, and not just by living things, according to researchers, reporting their results in the Oct. 27 issue of the journal Nature. Sun Kwok and Yong Zhang of the University of Hong Kong found that an organic molecule commonly found throughout the Universe contains a mixture of aromatic, or ring-like, and aliphatic, or chain-like, parts. These chemical structures resemble those of coal and petroleum, the researchers noted, types of organic material previously thought to arise only from living organisms. The researchers were investigating an unsolved puzzle: a set of infrared light emissions detected in stars and galaxies. For over two decades, it was widely thought that these “unidentified infrared emission features” come from simple organic molecules made of carbon and hydrogen atoms, called polycyclic aromatic hydrocarbons. But using data from the European Space Agency’s Infrared Space Observatory and NASA’s Spitzer Space Telescope, Kwok and Zhang concluded that the substances generating these emissions are much more complex. By analyzing the light of star dust formed in exploding stars called novae, they found that stars are making these complex organic compounds on extremely short time scales of weeks, and throwing them off into space. “Theoretically,” it’s “impossible” for stars to create these molecules, “but observationally we can see it happening,” Kwok said. The organic star dust is similar in structure to complex organic compounds found in meteorites, Kwok and Zhang added. Since meteorites are remnants of the early Solar System, the findings raise the possibility that stars enriched the early Solar System with organic compounds. The early Earth was subjected to severe bombardments by comets and asteroids, which might have carried organic star dust, the researchers speculate.