Picture a cool place, teeming with a multitude of hot bodies twirling about in rapidly changing formations of singles and couples, partners and groups, constantly dissolving and reforming. If you were thinking of the dance floor in a modern nightclub, think again. It's a description of the shells around dying stars, the place where newly formed elements make compounds and life takes off, said Katharina Lodders, Ph.D., research associate professor of earth and planetary sciences in Arts & Sciences at Washington University in St. Louis.
Chemistry for the very first time
“The circumstellar environment is where chemistry happens for the very first time,” said Lodders. “It's the first place a newly synthesized element can do chemistry. It's a supermarket of things from dust to gas and dust grains to molecules and atoms. The circumstellar shells enable a chemistry that produced grains older than our sun itself. It's generated some popular interest, and this year marks the 20th anniversary of the presolar grain discoveries.”
A star comes of age
Our sun and other dwarf stars of less than about ten solar masses burn hydrogen into helium in their cores. As they come of age, they become Red Giant stars and burn the helium to carbon and oxygen. But many heavy elements such as strontium and barium, even heavier than iron, are also produced, albeit in much smaller quantities than carbon. At the same time, the star begins to eject its outer layers into the interstellar medium by stellar winds, building up a circumstellar shell. So eventually, most of a star's mass, including the newly produced elements, is ejected into the interstellar medium through the circumstellar shell. Most interstellar grains come from such stars.