Dying stars suspected of seeding space with carbon nanotubes

(ORDO NEWS) — Among the metals – and this is how astrophysicists call the entire periodic table, with the exception of hydrogen and helium – carbon ranks second after oxygen in terms of abundance in the universe.

Curiously, even in interstellar space, this element occurs in a variety of forms, many of which require very specific conditions for formation. One of the most probable ways for the appearance of fullerenes and carbon nanotubes in outer space was revealed by American scientists.

The description of the study and the results of the experiments were presented by a team of specialists from the University of Arizona (USA) on June 16, at the 240th meeting of the American Astronomical Society in Pasadena (California).

The corresponding full-fledged scientific work has not yet been published, but is already being reviewed by the Journal of Physical Chemistry A .

The variety of allotropic modifications of carbon – that is, simple substances of one chemical element – is truly wonderful. In the case of the element that serves as the basis of all organic chemistry, about a dozen such forms are known.

And each of them is radically different from the rest in physical and chemical properties. Therefore, it finds the most diverse application both in nature and in human activity.

Graphite and diamond are used in people’s daily lives and in industry. Fullerenes and nanotubes can become the basis for breakthrough developments in medicine, technology and fundamental research.

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Fullerenes formed in the gas and dust nebula

Various allotropic modifications of carbon are common not only on Earth, but are also found everywhere in space. How graphite and diamond arise is known to science, but how fullerene molecules consisting of tens or even hundreds of atoms are formed outside laboratories is still not fully resolved.

Until recently, there were several proposed mechanisms for the formation of such molecules in nature. One of them was proposed three years ago by the lead author of the new study, Jacob Bernal, along with colleagues.

Scientists have found that when simulating the conditions that occur in the nebulae formed around dying stars, some of the carbon atoms form the most common fullerenes – C60.

These molecules are also called buckyballs or buckminsterfullerenes. They are balls of 60 carbon atoms, forming two dozen hexagons and 12 pentagons, from which a kind of ball is obtained. Sometimes fullerenes contain inclusions of other elements in their structure or even literally lock some atoms inside their own cavity.

The latter phenomenon allows scientists in some cases to recognize the isotopic and chemical composition of the ancient atmospheres of planets. Although C60 is the most common fullerene, there are stable molecules of both C20 and C70 , and even those with more than a hundred carbon atoms.

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Transmission electron microscope, with which it is possible to observe individual atoms

In addition to the ball, fullerenes can take quite a variety of forms – from onions to cylinders with rounded ends. Yes, carbon nanotubes are also fullerenes, just because of their very different properties, they are isolated into a separate allotropic modification.

Building on previous research on buckyballs, Bernal’s team set out to test the hypothesis that C60 doesn’t form alone in the vicinity of dying stars. In fact, American scientists repeated their experiment with several modifications.

One of them seems to have been more detailed spectroscopy. Since this time it was possible to detect not only spherical fullerenes, but also carbon nanotubes.

They were formed by heating silicon carbide ( SiC ) in a vacuum to 1050 degrees. At first, carbon atoms separated from silicon and formed buckyballs, but after a minute these structures began to roll into cylinders.

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Carbon atoms “peeling off” from silicon carbide and folding into fullerenes

During the experiment, nanotubes with a length of about three to four nanometers were observed, they were often multilayered, and the most voluminous consisted of four nested cylinders. The number of carbon atoms in these molecules easily exceeded a thousand.

Moreover, quite often, even before the end of formation, nanotubes were detached from the surface of a sample of silicon carbide and flew into the surrounding space. According to the researchers, this may be the main mechanism explaining the presence of cylindrical fullerenes in outer space.

In itself, the phenomenon of complex carbon molecules in interstellar space was discovered recently, about five years ago. Before that, extraterrestrial fullerenes were found only on meteorites. It is assumed that buckyballs and nanotubes should be found in appreciable amounts on comets and asteroids.

Bernal’s team will be able to test this hypothesis next year, when a capsule with a sample of the substance (101955) arrives on Earth by Bennu, who assembled the OSIRIS-REx apparatus.

The University of Arizona, represented by the Lunar and Planetary Laboratories , is a key partner in the mission, responsible for research and data processing.


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