The European Space Agency (ESA; Paris; (+) 33-153-697-654) infrared space observatory (ISO) has identified another star surrounded by a hazy cloud of an unidentified carbon compound. Many believe that the cloud is made of either small diamonds or buckyballs, although neither substance has ever been detected in space. Several major research groups around the world are now analyzing ISO's results. If they find that either diamonds or buckyballs have been created in space, researchers will gain new insight into the ideal conditions for manufacturing these two carbon forms.
Stars Tied To Unidentified Carbon (Back to Top)
The carbon compound was found in a dying star called IRAS 16594- 4656. Over the last thousand years, the star has blasted out huge amounts of material, enclosing itself in a shell of dust hundreds of times larger than the solar systema structure called a "protoplanetary nebula."
IRAS 16594-4656 is not the first star to be discovered with an intriguing carbonaceous compound around it. ISO also found another star that has a weaker emission spectrum. These findings raise the total number of stars associated with unidentified carbon compounds to 14. IRAS 16594- 4656 is one of the best representatives of this star type, as it emits a very strong signal of the carbon compound. The telescope observed it with a higher spectral resolution than those achieved with other stars in this class.
Neither diamonds nor fullerenes have ever been detected in space, but their presence has been predicted. Tiny diamonds of pre-solar originolder than the solar systemhave been found in meteorites, which supports the theory that they exist in space. Buckyballs have also been searched for extensively in space but never found.
International Research Investigations (Back to Top)
Astronomers hope that the ISO results will help identify the carbon compounds found around these stars. Several research groups are now debating the topic in astronomy institutes and chemistry laboratories around the world. At present, mixed teams of astrophysicists and chemists are investigating compounds whose chemical signature, or "fingerprint," matches that detected by ISO.
Using ISO's SWS and LWS spectrometers, a Spanish research group detected the signature of the carbonaceous compound in the dust surrounding the star. The signature came in the form of a broad emission band with a 21-micron wavelength. The dust was very cold and therefore invisible to non-infrared telescopes.
"We searched for the compound in 20 candidate stars and only this one had it," says ESA astronomer Pedro Garcia-Lario of the ISO Data Center (Villafranca, Madrid, Spain). "It is a real textbook case, with one of the strongest emissions ever detected. It gets us closer to solving the mystery and will help us to understand how the 'chemical factories' of the universe work."
Garcia-Lario's group believes that the particles are fullerenes. These would form when the solid carbon grains decompose. The grains are condensed out of the material emitted by the star. His group published their results in the March 10, 1999, issue of the Astrophysical Journal.
A Canadian research group investigating the carbonaceous compound obtained high-resolution ISO spectra of seven other stars in this class, and also detected a weak emission of the carbonaceous compound in a new one. Their data will be published in the May 11,1999, issue of the Astrophysical Journal Letters.
"Diamonds, graphite, coal, and fullerenes are different forms of carbon. It is quite possible that the 21-micron feature arises from any one of these forms, although not exactly like they are on Earth," says main author Sun Kwok of the University of Calgary (Canada). Ten years ago, his group detected the carbonaceous compound for the first time using the infrared satellite IRAS.
Meanwhile, results from a French research group led by Louis d'Hendecourt at the Institut d'Astrophysique Spatiale (Paris), are adding to the debate. The researchers isolated nanodiamonds from a sample of the Orgueil meteorite and analyzed them with infrared spectroscopy. They concluded that nanodiamonds that lack some of their lattice atoms have chemical signatures that closely match the chemical signature surrounding the mystery stars.
If the carbonaceous compound detected by ISO is a fullerene or a diamond, the research will provide new data on the production of these industrially interesting materials. If they are formed in the dust surrounding stars at relatively low temperatures and low pressures, companies could learn more about the ideal physical conditions needed to produce them.
About ISO (Back to Top)
ISO was put into orbit in November 1995 by an Ariane 44P launcher from the European Spaceport (Kourou, French Guiana). Its operational phase lasted until May 19, 1998, almost a year longer than expected. As an unprecedented observatory for infrared astronomy, ISO examined cool and hidden places in the universe. The telescope made nearly 30,000 scientific observations.
For more information, call Martin Kessler, ISO project scientist, at (+) 33-153-697-155 or fax (+) 33-153-697-690.