Stars as Molecular Factories

Abstract

A micrometer-size particle of stardust is made of billions of atoms. In the case of silicates, the atoms are oxygen, silicon, iron and magnesium. How did so many atoms aggregate themselves into a solid? On Earth, when atoms meet, they form molecules. Molecules are simple entities that consist of two or more atoms. The air we breathe contains primarily oxygen (O2) and nitrogen (N2) molecules, which are made of two oxygen and two nitrogen atoms, respectively. Water, one of the most common molecules on Earth, is made of two hydrogen atoms and one oxygen atom. The water molecule can be in a gaseous form (steam), liquid (water), or solid (ice). The ice crystal contains many water molecules arranged in fixed geometric patterns. If we think about the relationship between water and ice, we must realize that the first step to form ice is to have water molecules. This is also true for stardust. The first step to form silicates is to have simple oxide molecules. We can imagine that the atoms in the stellar atmosphere collide with each other, first forming simple gas-phase molecules which later aggregate into larger solids. Since we see stardust through the infrared radiation they emit, there must also be simple molecules in these infrared stars. The question is: how do we detect them?