discovered in space
by Amanda Doyle
for ASTRONOMY NOW
Posted: 28 February 2012
Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time.
A buckyball is comprised of 60 carbon atoms (it therefore also goes by the nickname of C60), which are arranged into a hollow sphere. The similarity of the shape to the architect Buckminster Fuller's geodesic domes earned the molecule the name buckminsterfullerene, or buckyball for short.
C60 molecules, or buckyballs, can stack together to form a solid. These solid particles have been detected for the first time in space. Image: NASA/JPL-Caltech.
Buckyballs exist on Earth such as in the gas escaping from a burning candle, and due to their unusual structure they also serve useful purposes in medicine and water purification. Buckyballs were predicted to exist in the cosmos in 1992, and the first discovery of C60 outside the Earth was made in 2010 by Spitzer. This C60 was in a gaseous form, and it has since been detected in various different environments.
However solid buckyballs in space have eluded astronomers until their discovery around the binary star XX Ophiuchi. The binary contains a cool red giant along with a hotter star. The exact spectral type of this hot star was a source of debate for quite some time as it was thought that “reddening” made the star look dimmer than it actually was. Reddening occurs when light is scattered by interstellar dust particles. If the hot star was reddened, then it meant that it was probably a main sequence star.
Further observations suggested that the reddening was overestimated and that the star was actually dim enough to be a subdwarf (below the main sequence) that was encapsulated within a dusty shell. “I thought this might be due to small silicate particles so I set about looking for evidence of silicates in infrared observations,” explains Nye Evans of Keele University, lead author of the discovery paper that appears in the Monthly Notices of the Royal Astronomical Society. “What I found however was not silicates but hydrocarbons – a complete surprise as hydrocarbons need a carbon-rich environment to form. A crude calculation suggested hydrocarbons containing a few tens of carbon atoms, interestingly close to the 60 needed for C60.”
XX Ophiuchi was then probed further with Spitzer. “We got two observations, only one showing clear evidence for C60,” Evans tells Astronomy Now. “The spectral signature is a little different from that of C60 in the gas phase, but is close to that of solid C60.”
The discovery of solid buckyballs in space implies that they are quite common in circumstellar environments, as a certain amount of molecules are needed to stack together to become solid particles. These results also suggest that more C60 may be waiting to be discovered around other hot stars.