Experiment shows how "synthetic" buckyballs form in interstellar space
A few years ago, astronomers detected complex carbon molecules – previously only thought to be made in a lab setting – floating around in interstellar space. How these so called buckyballs came to be out there remained a puzzle, but now scientists at the University of Arizona have managed to create them under space-like conditions, hinting at how they can naturally form between the stars.
Carbon comes in all sorts of strange configurations, but buckminsterfullerene is one of the weirdest. It’s made of 60 carbon atoms arranged in a lattice that forms a soccer ball shape – hence the nickname “buckyballs” or the official title of Carbon 60 (C60). After its creation in the lab in the 1980s, it was assumed to be too complicated to exist in nature.
But sure enough, in 2010 the Spitzer Space Telescope detected buckyballs floating around in interstellar space. Before then it was thought that most molecules in space would be small and simple, so the discovery of molecules made up of 60 atoms was a surprise.
Buckyballs were spotted in planetary nebulae – clouds of debris left over after stars go supernova. That could provide a clue to their origins, but it’s strange that the carbon remains pure in an environment where hydrogen molecules outnumber carbon by 10,000 to one.
"Any hydrogen should destroy (buckyball) synthesis,” says Jacob Bernal, lead author of the study. "If you have a box of balls, and for every 10,000 hydrogen balls you have one carbon, and you keep shaking them, how likely is it that you get 60 carbons to stick together? It’s very unlikely.”
And yet, buckyballs continue to float around out there. To investigate how and why, the researchers on the new study used transmission electron microscopes (TEMs) to simulate planetary nebula environments. These instruments are designed to work in a vacuum – similar to conditions in interstellar space – and allow scientists to closely study atoms.
The team started by placing silicon carbide, a type of dust common to supernovae, into the TEM. Then they cranked up the heat to 1,830° F (999° C) and beamed high-energy xenon ions at it. It was thought that this should remove the silicon, leaving just carbon behind.
"Sure enough, the silicon came off, and you were left with layers of carbon in six-membered ring sets called graphite," say Lucy Ziurys, co-author of the study. "And then when the grains had an uneven surface, five-membered and six-membered rings formed and made spherical structures matching the diameter of C60. So, we think we’re seeing C60."
With that result, the apparent story of how buckyballs form in space comes into focus. The team says that first, silicon carbide is released in supernova explosions. Then, while it’s floating around in interstellar space it’s exposed to high temperatures, shockwaves and radiation, which tears off the silicon and leaves carbon behind in the complex shape. And because buckyballs are stable to radiation, they can survive out there for billions of years.
The implications of this study are quite interesting, the team says.
"If this mechanism is forming C60, it’s probably forming all kinds of carbon nanostructures," says Ziurys. "And if you read the chemical literature, these are all thought to be synthetic materials only made in the lab, and yet, interstellar space seems to be making them naturally.”
The research was published in the Astrophysical Journal Letters.
Source: University of Arizona