The making of interstellar grit.

The making of interstellar grit

A common kind of sandpaper grit -- silicon carbide -- also serves as the primary kind of carbon particle that forms in the average red giant star, according to a group of scientists. In previous laboratory experiments, says Michael Frenklach of Pennsylvania State University Park, "everyone else proposed that the nucleation of interstellar grains occurs at temperatures around 1,000 kelvins. We are proposing the nucleation [of silicon carbide] begins at much higher temperatures--2,000 kelvins and above."

Frenklach and his colleagues report in the May 18 NATURE that their experiments are the first to take into account the high concentrations of hydrogen surrounding red giant stars. The group determined that hydrogen suppresses production of carbonaceous material like soot or graphite, but not of silicon carbide. This, combined with the abundance of silicon and carbon in the universe, "makes it more likely that silicon carbide is probably the first particle to condense." The scientists say they believe these grains condense at the high temperatures near the star, while other materials form farther out in the stellar atmosphere, where temperatures are low.