Fredagskollokvium: A non-dark matter mystery: the quest for the origin of heavy elements
Ann-Cecilie Larsen, Post.doc., Dep. of Physics/SAFE, University of Oslo
The recent Planck results on the cosmic microwave background indicate an energy budget of the Universe where ordinary matter comprises only 4.9% . Despite this small fraction, ordinary matter is literally of vital importance, as atoms are (as far as we know) the building blocks of all life forms. Indeed, "We are made of star-stuff" , and life as we know it would not be possible without the creation of elements such carbon, oxygen, and iron during stars' life and death.
Nuclear processes in stars provide the energy that makes them shine, and the same processes contribute to the cooking of lighter elements. Depending on the initial mass of the star, elements up to the iron group can be produced via fusion, i.e. smashing two atomic nuclei into each other to make one big nucleus. However, elements heavier than iron cannot be reached through fusion. Burbidge, Burbidge, Fowler and Hoyle , and independently Cameron , realized that the only way to create heavy elements in significant amounts (as observed in the solar system) is via neutron-induced reactions. Two main processes were identified: the slow neutron-capture (s-) and the rapid neutron-capture (r-) process. For the latter, a huge flux of neutrons are needed in the astrophysical environment in order to explain the abundance pattern found in the solar system. For long, it was thought that core-collapse supernovae could do the trick, but recent state-of-the-art simulations seem to miss the necessary conditions (too few neutrons). The r-process is a big mystery and one of the major open questions in nuclear astrophysics (e.g. ).
In this talk, I will discuss the heavy-element nucleosynthesis, in particular a newly started project on the so-called Rhenium-Osmium cosmochronology in collaboration with ITA. I will also discuss astrophysical uncertainties related to the r-process, and the nuclear-physics input crucial for realistic r-process abundance calculations. Finally, I will mention briefly our experimental  and theoretical  efforts on the nuclear-physics side to provide constraints for this fascinating and still elusive process.