Astronomers have found evidence of buckyballs — carbon molecules shaped like soccer balls — in the nebula around a distant white dwarf star. The discovery marks the largest molecules known to exist in space.
Normally found in chemistry labs, where they are made by vaporizing graphite in the presence of helium, buckyballs were long suspected to form inside stars.
"As soon as they were discovered in the lab it was actually suggested they would be very good candidates to be found in space," astronomer Jan Cami of the University of Western Ontario, who led the new study, told Space.com.
Researchers had searched for buckyballs before in the gas and dust between and around stars, but the evidence was inconclusive. Cami and his colleagues identified buckyball molecules, known as C60 because they are made of 60 carbon atoms each.
The buckyballs are about 1 nanometer in size, about three times larger than water molecules, which are about 0.3 nanometers in size and consist of three atoms (one oxygen atom and two hydrogen atoms). One nanometer is a billionth of a meter, or about one ten-thousandth the diameter of a human hair.
The buckyball molecules were discovered in the planetary nebula Tc-1, which is about 6,500 light-years away in the southern constellation Ara. Despite their name, planetary nebulas are actually clouds of gas around stars, not planets.
"What we see is a very clean and very recognizable fingerprint for only two species," Cami said — C60 and a closely related molecule called C70, made of 70 carbon atoms. Both C60 and C70 belong to a class of molecules termed buckminsterfullerenes, or just fullerenes, after architect Buckminster Fuller.
Together the two fullerenes make up about 3 percent of the available carbon around the star, the researchers reported.
Tc-1 contains what is known as an asymptotic giant branch (AGB) star. The inner regions of these stars have become dense, dim stars called white dwarfs, while their outer stellar envelopes have sloughed off. The resulting cloud of shed layers undergoes chemical reactions and is ionized by radiation from the inner white dwarf, creating a planetary nebula that will eventually become part of the interstellar medium.
Large molecules in space
The new finding came when a colleague of Cami's was looking at infrared data from the Spitzer Space Telescope. Every molecule in space soaks up infrared light at a unique set of wavelengths, resulting in a kind of chemical fingerprint.
"He had this one object that looked very strange to him," Cami said. "The spectrum didn't look quite like anything he had seen before."
Normally the nebula around an AGB star will contain hydrogen, which inhibits the reaction that produces fullerenes, and also tends to obscure any signal from the molecules.
The researchers think C60 and C70 were able to form on sooty dust grains because the Tc-1 nebula lacked hydrogen gas.
Based on the observed temperature of the fullerenes, they estimate that the molecules formed within the past 100 years and would likely be undetectable in another 100 years.
The finding "shows that complex, large molecules can exist in space," said astrophysicist Theodore Snow of the University of Colorado in Boulder, who was not involved in the research. "Buckyballs are very stable and resistant to interstellar ultraviolet radiation, so once formed they can have long lifetimes in space."
The researchers detailed their findings in the July 23 issue of the journal Science.