OUTER space grows “carbon onions”, say scientists in Belgium. They claim that
families of exotic carbon molecules explain a property of interstellar dust that
has perplexed astronomers for decades.
In the mid-1960s, astronomers realised that interstellar dust absorbs
ultraviolet light from distant stars in a broad band of wavelengths close to 217
nanometres. Possible culprits for the absorption included naphthalene, graphite
and small fullerenes such as buckyballs (C60), but none fitted the bill
exactly. “The composition of interstellar clouds is a very old mystery,” says
Luc Henrard of the University College of Notre Dame de la Paix in Namur,
But carbon onions—families of fullerenes nested together like Russian
dolls—could be the answer, say Henrard and his colleagues in The
Astrophysical Journal (vol 487, p 719). Their calculations suggest that
clouds of onions, with each onion no more than 20 nanometres across, could
create the right absorption pattern if they had a coating of water. Loosely
bound electrons in the onions would soak up the energy and vibrate in phase with
Henrard suspects that these molecules begin their lives as microscopic
diamonds in the atmospheres of stars. With energy from radiation in space they
could turn into carbon onions, just as onions form in laboratory experiments
when tiny diamonds reach a temperature of about 1000 °C.
“The thing that concerns me is that no one has proved that fullerenes exist
in space,” comments Thomas Wdowiak of the University of Alabama at Birmingham.
He suspects that the real culprit will be an interstellar molecule that has
already come to light, such as naphthalene. Wdowiak and his colleagues contend
that groups of large molecules containing naphthalene can also create the right
absorption pattern (The Astrophysical Journal, vol 487, p 976).