Stellar Alchemy: Genesis of Heavy Elements
Anna Frebel, Massachusetts Institute of Technology
The first billion years after the Big Bang led to the rise of the chemical elements in the universe. In the primordial universe, elements heavier than hydrogen and helium were forged in the very massive first stars and dispersed into space during their subsequent supernova explosions. Since then stars have formed from gas that was enriched in elements such as carbon or iron, and with every stellar generation the amount elements in the universe has steadily increased. The oldest stars that still survive (to to their low masses) since their birth in the early universe 12 to 13 billion years ago offer astronomers the chance to study the chemical composition of these early, heavy element deficient gas clouds. Because these stars preserve their birth cloud chemical composition in their atmospheres, we can study, retrospectively, the various nucleosynthesis processes that created the different elements. I will detail the concept of "stellar archaeology" by discussing a rare group of old stars that display a strong overabundance of the heaviest elements, in particular uranium and thorium. They can thus be radioactively dated, giving formation times ~ 13 Gyr ago, similar to the ~ 13.8 Gyr age of the Universe. This way we can trace the origin and evolution of the elements from lithium to uranium.
Background Review Articles:
Frebel, Anna. "Four Starry Nights." Scientific American 307.6 (2012): 64-69.
Frebel, Anna, et al. "Nucleosynthetic signatures of the first stars." Nature 434.7035 (2005): 871-873.