INFO 07-1999: Astronomers debate diamonds in space
23 April 1999Most chemical elements in the Universe are produced in the stars, and thus the stars' environments act as huge chemical factories. The European Space Agency's infrared space telescope, ISO, has detected, in the dust surrounding a star, the chemical signature of a mysterious compound made of carbon, whose nature is being actively debated by astronomers all over the world. While some say it could be a very tiny diamond, others think it is the famous football-shaped molecule called "fullerene" or "buckyball". If either of these hypotheses is confirmed it will be interesting news for industry as well.
This is not the first time the intriguing carbonaceous compound has been detected in space. A peculiar elite of twelve stars are known to produce it. The star now added by ISO to this elite is one of the best representatives of this exclusive family, since it emits a very strong signal of the compound. Additionally ISO found a second new member of the group with weaker emission, and also observed with a spectral resolution never achieved before other already known stars in this class.
Astronomers think these ISO results will help solve the mystery of the true nature of the compound. Their publication by two different groups, from Spain and Canada, has triggered a debate on the topic, both in astronomy institutes and in chemistry laboratories. At present, mixed teams of astrophysicists and chemists are investigating in the lab compounds whose chemical signature or "fingerprint" matches that detected by ISO.
Neither diamonds nor fullerenes have ever been detected in space, but their presence has been predicted. Tiny diamonds of pre-solar origin - older than the Solar System - have been found in meteorites, which supports the as yet unconfirmed theory of their presence in interstellar space. The fullerene molecule, made of 60 carbon atoms linked to form a sphere (hence the name "buckyball"), has also been extensively searched for in space but never found.
If the carbonaceous compound detected by ISO is a fullerene or a diamond, there will be new data on the production of these industrially interesting materials. Fullerenes are being investigated as "capsules" to deliver new pharmaceuticals to the human body. Diamonds are commonly used in the electronics industry and for the development of new materials; if they are formed in the dust surrounding some stars, at relatively low temperatures and conditions of low pressure, companies could learn more about the ideal physical conditions to produce them.
A textbook case
The latest star in which the compound has been found is called IRAS 16594-4656. Like the others, it's a carbon-rich star now in the process of dying. It has been blasting out huge amounts of material over the last thousand years, becoming enclosed within a shell of dust hundreds of times larger than the Solar System - a structure called a "protoplanetary nebula".
It was in this dust - very cold and therefore invisible to non-infrared telescopes - that the Spanish group using ISO's SWS and LWS spectrometers detected the signature of the carbonaceous compound, in the form of a broad emission band at the wavelength of 21 micron.
"We searched for the compound in twenty candidate stars and only this one had it. 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," says ESA astronomer Pedro Garcia-Lario at the ISO Data Centre in Villafranca, Madrid. His group published their results in the March 10 issue of the Astrophysical Journal.
They favour the fullerene option. Fullerenes would get formed during decomposition of the solid carbon grains condensed out of the material emitted by the star.
The Canadian group 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. They present their data in the May 11 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, at the University of Calgary. His group detected the carbonaceous compound a decade ago, for the first time, with the earlier infrared satellite IRAS.
Meanwhile, results from the French group led by Louis d'Hendecourt, at the Institut d'Astrophysique Spatiale, in Paris, are adding to the debate. They isolated very tiny diamonds - a million times smaller than a millimetre and thus called "nanodiamonds" - from a sample of the Orgueil meteorite, and then subjected them to infrared spectroscopy. The researchers conclude that nanodiamonds of a certain kind, defective ones in which some atoms of the lattice are missing, have a "chemical signature" that matches the one detected in the stars very closely.
Footnote on ISO
ESA's infrared space telescope, ISO, was put into orbit in November 1995, by an Ariane 44P launcher from the European Spaceport in Kourou, French Guiana. Its operational phase lasted till 16 May 1998, almost a year longer than expected. As an unprecedented observatory for infrared astronomy, able to examine cool and hidden places in the Universe, ISO made nearly 30 000 scientific observations. These are now available to the scientific community via the ISO Archive (http://www.iso.vilspa.esa.es) at the ISO Data Centre, in Villafranca, near Madrid, Spain.
For More Information, please contact:
ESA Public Relations Division: Tel: +33(0)18.104.22.168.55
Martin F. Kessler, ISO Project Scientist:
ESA's Satellite Tracking Station in Villafranca (Spain)
Tel.: + 34 91 813 1253
Pedro Garcia-Lario (ISO Data Centre)
Tel: +34 918131389
Other science contact points:
Dept. of Physics and Astronomy University of Calgary, Canada
Louis d'Hendecourt Directeur de Recherches CNRS
Institut d'Astrophysique Spatiale, Orsay, France
Tel: +33 (0)1 69858640
The four ISO instruments were built by large international teams led by:
Principal Investigator: Dr. Catherine Cesarsky
CEA, Saclay, France
Tel: +33.1 - 69.08.7515 cesarskycea.fr
Principal Investigator: Prof. Dietrich Lemke
MPI Fur Astronomie, Heidelberg, germany
Tel: +49 6221.528.259
Short-Wavelength Spectrometer (SWS)
Principal Investigator: Dr Thijs de Graauw
Lab. for Space Research, Groningen, The Netherlands
Tel: + 31.50.363.4074
Long-Wavelength Spectrometer (LWS)
Principal Investigator: Prof. Peter Clegg
Queen Mary and Westfield College, London, UK
Tel: + 44.171.975.5038