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Surprising chemicals found among stars

July 23, 2007
Courtesy NRAO
and World Science staff

As­tro­no­mers are mak­ing some sur­pris­ing chem­i­cal finds among stars—dis­cov­eries that they say add to the num­ber of known ways in which mol­e­cules needed for life could form.

In less than a year, re­search­ers say they have found the first three mol­e­cules in space with neg­a­tive elec­tri­cal charge. Such mol­e­cules have an ex­cess of elec­trons, neg­a­tively-charged sub­a­tom­ic par­t­i­cles.

Artist's di­a­gram show­ing mod­els of neg­a­tive­ly charged mo­le­cules near a star. The long, straight mod­el un­der­neath the down­ward-point­ing ar­row rep­re­sents the new­found oc­tate­tray­nyl an­ion. See here for a full dia­g­ram show­ing how it forms. 
“This dis­cov­ery con­tin­ues to add to the di­vers­ity and com­plex­ity that is al­ready seen in the chem­is­try of in­ter­stel­lar space,” said An­tho­ny J. Remi­jan of the Char­lottes­ville, Va.-based Na­tional Ra­di­o As­tron­o­my Ob­serv­a­to­ry. 

“It al­so adds to the num­ber of paths avail­a­ble for mak­ing the com­plex or­gan­ic mol­e­cules,” the in­gre­di­ents of life, he added. Such sub­stances are thought to have formed in the same gi­ant clouds that give rise to stars and plan­ets.

In the July 20 is­sue of the re­search jour­nal As­t­ro­phys­i­cal Jour­nal Let­ters, two teams of as­tro­no­mers an­nounced find­ing the third neg­a­tively charged chem­i­cal, known as oc­tate­traynyl an­ions. 

The mol­e­cules are rec­og­niz­a­ble by char­ac­ter­is­tic fre­quen­cies, or en­er­gies, of ra­di­o waves that they emit, sci­en­tists said.

The mol­e­cules, which con­sist of chains of eight car­bon at­oms and one hy­dro­gen at­om, turned up in the en­ve­lope of gas around an old star and in a cold, dark cloud of mo­lec­u­lar gas. The re­search­ers used da­ta from the Na­tional Sci­ence Founda­t­ion’s Rob­ert C. Byrd Green Bank Tel­e­scope in Green Bank, W. Va. 

Pre­vi­ously, only mol­e­cules with neu­tral or pos­i­tive charge were known. A neu­tral mol­e­cule has just enough elec­trons to can­cel out positive charges within the atoms of the mo­le­cule. Positive mo­le­cules have few­er than this num­ber of elec­trons; neg­a­tive mo­le­cules, more.

About 130 neu­tral and about a doz­en pos­i­tively-charged mol­e­cules have been dis­cov­ered in space, but the first neg­a­tively-charged mol­e­cule was not dis­cov­ered un­til late last year, re­search­ers said. Among the neg­a­tively charged mol­e­cules, the new­found one is the larg­est.

“Un­til re­cent­ly, many the­o­ret­i­cal mod­els of how chem­i­cal re­ac­tions evolve in in­ter­stel­lar space have largely ne­glected the pres­ence of an­ions,” or neg­a­tively charged mol­e­cules, said Jan M. Hol­lis of NASA’s God­dard Space Flight Cen­ter in Green­belt, Md. “This can no long­er be the case.” It was pre­vi­ously thought that ul­tra­vi­o­let light would knock ex­tra elec­trons off any mol­e­cules, pre­vent­ing any from tak­ing on a neg­a­tive charge.

Hol­lis and Remi­jan are mem­bers of one of the re­search teams re­port­ing the find­ings in As­t­ro­phys­i­cal Jour­nal Let­ters. The oth­er team con­sisted of re­search­ers with the Har­vard-Smith­son­ian Cen­ter for As­t­ro­phys­ics in Cam­bridge, Mass.

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Astronomers are making some surprising chemical finds among stars—discoveries that they say add to the number of ways in which molecules needed for life could form. In less than a year, researchers say they have found the first three molecules in space with negative electrical charge. Such molecules have an excess of electrons, negatively-charged subatomic particles. Previously, only molecules with neutral or positive charge were known. “This discovery continues to add to the diversity and complexity that is already seen in the chemistry of interstellar space,” said Anthony J. Remijan of the Charlottesville, Va.-based National Radio Astronomy Observatory. “It also adds to the number of paths available for making the complex organic molecules,” the ingredients of life, he added. Such substances are thought to have formed in the same giant clouds that give rise to stars and planets. In the July 20 issue of the research journal Astrophysical Journal Letters, two teams of astronomers announced finding the third negatively charged chemical, known as octatetraynyl anions. The molecules are recognizable by characteristic frequencies, or energies, of radio waves that they emit, scientists said. The molecules, which consist of chains of eight carbon atoms and one hydrogen atom, turned up in the envelope of gas around an old star and in a cold, dark cloud of molecular gas. The researchers used data from the National Science Foundation’s Robert C. Byrd Green Bank Telescope in Green Bank, W. Va. About 130 neutral and about a dozen positively-charged molecules have been discovered in space, but the first negatively-charged molecule was not discovered until late last year, researchers said. Among the negatively charged molecules, the newfound one is the largest. “Until recently, many theoretical models of how chemical reactions evolve in interstellar space have largely neglected the presence of anions,” or negatively charged molecules, said Jan M. Hollis of NASA’s Goddard Space Flight Center in Greenbelt, Md. “This can no longer be the case.” It was previously thought that ultraviolet light would knock extra electrons off any molecules, preventing any from taking on a negative charge. Hollis and Remijan are members of one of the research teams reporting the findings in Astrophysical Journal Letters. The other team consisted of researchers with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.