We work in the field of nuclear astrophysics using a special approach by combining work in astrophysics theory and nuclear physics experiments.
Nuclear Astrophysics is a rather wide, interdisciplinary, and very exciting field of research. The goal is to understand the nuclear processes that occur naturally in our universe. Nuclear reactions created, and still create, the chemical elements our world is made of. Nuclear reactions make the sun and all the stars shine, and nuclear reactions power the greatest fireworks in our universe - star explosions like supernovae, novae, and X-ray bursts.
Despite of more than 50 years of research, where great progress has been made, some of the most important questions in nuclear astrophysics are still unanswered. Here are two examples that we think are among the most important ones and which are the focus of our research program: We believe today that we have more or less identified the different processes that synthesized the chemical elements in our universe, yet, we still don't know where in the universe one of the most important processes operates. This is the rapid neutron capture process (r process) which creates so important elements like gold and uranium. Some suspect supernova explosions, others prefer the crash of two neutron stars but all the proposed sites have their problems. Another important open question concerns one of the most fascinating objects in our universe: neutron stars. They are more massive than our sun, yet their radius is only that of a small city (6 miles) and they rotate so rapidly that a neutron star day can last less than a second. Neutron stars represent the most compact state of matter - a table spoon full of neutron star matter weighs 500 million tons. Yet, we don't know what the interior of neutron stars is made of, what the conditions in its interior are and how magnetic fields are created and evolve.
This is a time of great promise for nuclear astrophysics, as a new generation of astronomical observatories (like Chandra or, hopefully soon, INTEGRAL) provides unprecedented data, for example on supernovae, the r process, and neutron stars. However, these data can only lead to a solution of the problems outlined above, if we understand the underlying nuclear processes in the observed events. This is were our research comes in - we try to model the nuclear reaction sequences in the astrophysical events to analyze where crucial nuclear data are missing. We then design experiments to measure these data, and once that is done we go back to the model and determine how the new result changes our understanding of the astrophysical scenario. Luckily, the recent progress in astronomy coincides with a number of new nuclear physics facilities becoming operational world wide, including the coupled cyclotron facility at MSU. This opens up the opportunity for a long list of experiments needed for nuclear astrophysics.
Our program focusses on the r process (see above) and on nuclear explosions on the surface of neutron stars. While neutron stars contain no nuclear "fuel", there are a number of them that are part of a binary system - a solar system with two stars instead of one. If the neutron star gets close enough to its "normal" companion star, it starts sucking matter from his companion onto his surface, where it produces thermonuclear explosions as frequently as several per hour. These explosions are observed as X-ray bursts and provide information about the neutron star - if one understands the reactions during the explosion (this is called the rapid proton capture process, or rp process). Both, the r- and the rp- processes involve nuclei that are very unstable - most of them live less than a second. In the r process these are very neutron rich isotopes, in the rp process very proton rich isotopes. The majority of these nuclei has in fact never been observed in a laboratory and it is not clear whether current nuclear theories can be used to describe them. Our experiments focus on the properties of these very exotic nuclei. The coupled cyclotron at MSU is a unique facility for this type of experiments as the production rates for a large range of exotic, very unstable nuclei are the highest in the world.