An Experiment May Explain What Role Supernovas Have in Creating Heavier Elements
May 15, 2012; 9:30 AM
The Big Bang only produced the lightest elements, such as hydrogen and helium. One of the fundamental questions of astrophysics is how all the other elements were formed. In 1957, American researchers concluded that elements were formed through nuclear reactions inside stars.
Astrophysicists have believed that half the elements which are heavier than iron were formed in gigantic star explosions, known as supernovas. However, there is one little snag with this theory:
Astrophysicists have had huge problems making sense of the computer simulations of a supernova.
The simulations are based on certain characteristics of the atomic nucleus that are taken for granted but which have never been tested, as these characteristics are hard to determine.
Now, experiments carried out at the University of Oslo show that astrophysicists are using the wrong data in their models. The new results may have a great impact.
Nuclear physicists at the University of Oslo have measured the energy states of the elements iron and molybdenum. All the experiments were conducted in the cyclotron laboratory at the University of Oslo, where nuclear physicists can measure what happens when atomic nuclei collide with each other at very high speeds.
One of the problems with simulations is that no one knows what happens when nuclear reactions move beyond the well-known nuclei and out to the very exotic ones that are not found in nature.
Atomic nuclei consist of a good mix of protons and neutrons. The definition of an element is determined by the number of protons. The physical characteristics of elements depend also on the number of neutrons. The various states are called isotopes.
When it gets really hot, such as inside a star or a supernova, neutrons may be released and fuse with other atoms. When one of the neutrons of an atom emits an electron, the neutron turns into a proton. Then the atom has been transformed into a heavier element.
Nuclear physicists can calculate the probability of a physical transition between different elements. The known isotopes have been measured in laboratories. However, there are many isotopes which have not been measured. The limits of the number of these isotopes are unknown.
In a supernova explosion you need a large enough number of neutrons available. At the moment there seems to be more protons than neutrons in a supernova.
This is precisely where the research comes in. As long as the supernova has a sufficient amount of neutrons, astrophysicists can, with the help of the new findings from the University of Oslo, produce better simulations in the number and types of elements formed in a supernova. With research, these astrophysicists may be better able to understand what happens when a star goes supernova.
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