Evidence suggests that carbon nanotubes, small tubes composed of pure carbon, may form in the dust and gas envelopes surrounding dying stars. The findings suggest a simple but elegant mechanism for the formation and survival of complex carbon molecules in space.
In the mid-1980s, the discovery of complex carbon (Deadly stars can scatter in an interstellar environment using carbon nanotubes) molecules floating in an interstellar environment attracted much attention, perhaps the best known being the Buckminster fullerene or “buckyballs” spheres of 60 to 70 carbon atoms. However, scientists are trying to understand how these molecules form in space.
In an article accepted for publication in the Journal of Physical Chemistry A, researchers from the University of Arizona proposed a surprisingly simple statement. After exposing silicon carbide – a common component of dust grains in planetary nebulae – to conditions similar to those around a dying star, researchers observed the rapid formation of carbon nanotubes, which are molecular rod structures consisting of several layers of carbon plates. . The findings were presented on June 16 at the 240th meeting of the American Astronomical Society in Pasadena, California.
The work was led by Jacob Bernal, a researcher from the UAE, and builds on research published in 2019, when the group showed that it could produce buckyballs with the same experimental setup. The work suggests that buckyballs and carbon (Survival of complex carbon molecules in space) nanotubes may form when silicon carbide dust produced by stellar stars is hit by high temperatures, shock waves, and high-energy particles, with silicon leaching from the surface and remaining on the carbon.
The findings support the idea that stellar stars in the interstellar environment may scatter with nanotubes and possibly other complex carbon molecules. The results have implications for astrobiology because they provide a mechanism for the concentration of carbon that can be transported by planetary systems.
“We know from infrared observations that buckyballs live in an interstellar environment,” said Bernal, a postdoctoral fellow at Arizona Lunar and Planetary Laboratory. “The big problem is explaining how these large, complex carbon molecules can form in an environment full of hydrogen, which is normally what you get around a dying star.”
The formation of carbon-rich molecules, especially pure carbon species, in the presence of hydrogen is almost impossible by thermodynamic laws. The study’s new findings offer an alternative scenario: Instead of collecting individual carbon atoms, bucky balls and nanotubes (Survival of complex carbon molecules in space) may be the result of a simple structural arrangement of graphene-like carbon sheets, which are known to form on heated silicon carbide grains.
This is exactly what Bernal and his co-authors observed when heating and describing commercially available silicon carbide samples to temperatures occurring in dying or dead stars. As the temperature approached 1050 degrees Celsius, tiny hemispherical structures approximately 1 nanometer in size were observed on the grain surface. Within a few minutes of continuous heating, the spherical buds begin to grow into rod-shaped structures with numerous graphene layers with a curvature and tubular shape. The resulting nanotubes vary from about 3 to 4 nanometers in length and width, much larger than buckyballs. Most of the described samples are composed of more than four layers of graphite carbon. During the heating experiment, the tubes were observed to vibrate before reaching the surface and absorbing the vacuum around the problem.
“We were amazed that we were able to create these unique structures,” Bernal said. “Chemically, our nanotubes are very simple, but they are much nicer.”
Named after similarities to the architectural works of Richard Buckminster Fuller, fullerenes are the largest molecules now known to occur in interstellar space, which for decades was believed to lack a molecule with many atoms. , for the most part 10. It has now been found that the C60 and C70 fullerenes, each containing 60 or 70 carbon atoms, are common constituents in the interstellar medium. One of the first of its kind in the world, the transmission electron microscope located at the Kuiper Materials Imaging and Characterization Facility in Arizona, is uniquely suited to mimic the environment of planetary nebulae. An electron beam of 200,000 volts can detect mass up to a distance of 78 picometers – which is the distance of two hydrogen atoms in a molecule of water – which allows it to detect individual atoms. The device operates in a vacuum similar to the pressure – or less – that is assumed to exist in circumstellar environments.
While the spherical C60 molecule measures 0.7 nanometers in diameter, the nanotube structures created in this experiment measure several times the size of C60 and rapidly exceed 1000 carbon atoms. The study’s authors are convinced that their experiments accurately mimic the temperature and density conditions expected in the planetary nebula, said co-author Lucy Ziurys, a professor of astronomy, chemistry and biochemistry at UArizona. rulers. “We know the raw material is there and we know the conditions are very close to what you see near the shooting star,” he said. “There are shock waves that pass through the envelope, so the temperature and pressure conditions in space are manifested. In these planetary nebulae, we also see buckyballs – in other words, we see the beginning and end products you expect. In our experiments.” ”
These simulation experiments suggest that carbon nanotubes along with small fullerenes are then injected into the interstellar medium. Carbon nanotubes are known for their high resistance to radiation, and fullerenes can last for millions of years if they are adequately protected from high-intensity cosmic radiation. These structures may also have carbon-rich meteorites, such as carbon chondrites, scientists have suggested. According to co-author of the study Tom Zega, professor of the Lunar and Planetary Laboratory of the United States, the task is to find nanotubes of these meteorites due to their very small grain size and because meteorites are a complex mixture of organic and inorganic substances. materials, inter alia. with a size similar to nanotubes.
“However, our experiments suggest that such materials may form in interstellar space,” Zega said. “If they can survive the journey to our local part of the galaxy, where our solar system formed about 4.5 billion years ago, then they can be preserved in the remaining material.”
Zega said that a prime example of such residual material is Bennu, a carbonaceous near-Earth asteroid where NASA’s NASIRIS REx mission, led by NASA’s Arizona, took a sample in October 2020. Scientists are eagerly awaiting the arrival of this sample. 2023
“The asteroid Bennu may have stored these materials, so it is possible that we will find nanotubes in them,” Zega said.
