Project
Summary
The evolution of stars – from their inception from cosmic dust to their death by supernova implosion-explosion (in the case of massive stars) or by conversion into a white dwarf (in the case of less massive stars) – is a field of immense significance in physics and astronomy. An important part of stellar evolution is the burning of nuclear fuel, which takes place throughout the star’s life and is the mechanism that prevents the star’s huge gravitational pull from causing its own collapse. Nuclear matter within the star evolves through various types of reactions that transform lighter elements, such as hydrogen, into heavier nuclei, such as helium, carbon etc. Depending on the mass of the star, the nuclear composition of the inner core determines that certain reactions will dominate the burning process. In the Sun, a star with relatively small mass, the dominant reaction is the transformation of hydrogen into helium, whereas in stars that are more massive the reactions involve the transformation of heavier elements (e.g., oxygen, neon etc.) into even heavier elements. Indeed, the transmutation of elements – from those that existed shortly after the Big Bang (e.g., hydrogen, helium, lithium etc.) into much heavier ones, such as lead and uranium – is caused by chains of nuclear reactions within the stars through the process of fusion.
In several steps of these chains, radioactive elements are produced that do not exist in nature, but are important links between one part of the chain and the next. It is evident that the study of the fusion of these radioactive nuclei – such as 11Li (3 protons + 8 neutrons) and 230U (8 protons + 15 neutrons) – is highly important. With this project being developed at IEA-USP, we hope to dedicate ourselves to this type of research. Our study will include regular meetings of discussion and debate with renowned scholars from within and outside the University of São Paulo, as well as from abroad, the development of research projects, and resulting publication of scientific papers.
Justification
Our study involves issues in physics and astrophysics that are not regularly raised at USP’s Institute of Physics and Institute of Astronomy and Geophysics. We will use the non-extensive statistics of Constantino Tsallis (from the Brazilian Center for Physics Research – CBPF – in Rio), which applies a non-additive definition of entropy (lack of information), contrary to the usual Boltzmann-Gibbs definition.
Non-additive entropy allows us to study the question of stellar and universal evolution (cosmology). In addition, we will study current problems in nuclear astrophysics.
Scientific and social impacts
Clearly, the study of the universe and of stars captures the imagination of the lay population in general, besides being an intellectual activity of great scientific value. The ability to answer questions such, Where does chlorine or lead or the elements that compose our bodies (hydrogen, oxygen, calcium etc.) come from?, fascinates scientists and laypeople alike. The scholarly activities to be developed by IEA-USP will bring obvious benefits in raising community awareness of these questions and their possible answers.
In monthly meetings, the group intends to discuss the various aspects of the nuclear evolution of stars, specifically with regards to the involvement of unstable nuclei and the use of Tsallis’ statistics. The group also plans to study nuclear evolution in binary stars, such as Eta Carinae. This two-star system, in which the smaller feeds the larger, undergoes a “blackout” every 5.52 years and has a very high nuclear fuel burn rate (the blackout was foreseen and studied by astrophysicist Augusto Damineli, from IAG-USP). There is still no known or understood mechanism to explain this acceleration in burning.
The group aims to discuss and study this question, as well as the fact that the system turns with an extremely high rotational speed. In this case, the study involves the effect of a force commonly known as Coriolis, which originates from the rotation (one of the so-called non-inertial forces), on the nuclear reaction rate. Laboratory studies of the effect of magnetic fields on low-energy nuclear fusion (i.e., equivalent to the core temperature of commons stars or to the surface temperature of the primary star in two-star systems) show that the likelihood of tunneling (the quantum effect responsible for fusion) is enormously increased. It is expected that the Coriolis force, which has the same characteristics as the magnetic force, will also result in an increase in the nuclear fusion rate of binary star systems.
This project includes the participation of physicists from IFUSP, from the Rio de Janeiro Federal University, and from the Brazilian Center for Physics Research (CBPF).
Internal meetings timetable
The group will organize one or two “workshops” per year. The first, in February/March 2011, will be attended by 15 to 20 participants, and may include foreign scholars. The other workshop, national in scope, will be held in the second half of 2011 (October or November), with lectures in Portuguese for 20 participants from Brazil. The summaries, lectures etc. from these workshops will be published as a special issue of IEA’s Estudos Avançados journal or as a minutes book. We would like to acknowledge FAPESP’s support through the theme project under our responsibility (Proc. No. 2011/19889-2).
Production
1. Original scientific articles (papers) in nuclear astrophysics and related fields. Since Professor Mahir Hussein joined the IEA as a Visiting Scholar in 2011, he has published a total of 14 articles in renowned international journals. Two of his articles dealing with the subject matter of this proposal have now been accepted for publication.
2. Articles of scientific dissemination. Minutes (proceedings) of the project’s meetings, in both electronic and printed form. Summaries, lectures etc. of the workshops will be published as a special issued of IEA’s Estudos Avançados journal or as a minutes book.
Brazilian contributors
1. Alinka Lepine - IFUSP
2. Rubens Lichenthaler - IFUSP
3. Valdir Guimarães - IFUSP
4. Leandro Gasques - IFUSP
5. Luiz Carlos Chamon - IFUSP
6. Mauricio Porto Pato - IFUSP
7. Elcio Abdalla - IFUSP
8. Luis Felipe Canto - IFUFRJ
9. Paulo Roberto S. Gomes - IFUFF
10. Jesus Lubian - IFUFF
11. Antonio F. R. de Toledo Piza - IFUSP
12. Constantino Tsallis - CBPF
Probable international contributors
The project may also count on the support and participation of a reasonable number of renowned researchers from abroad.
1. Carlos Bertulani, Texas A&M University, USA.
2. Pedro Avelino, Universidade do Porto, Portugal.
3. Pierre Descouvemont, Université Libre de Bruxelles, Belgium.
4. Shigeru Kubono, University of Tokyo, Japan.
5. Michael Wiescher, Notre Dame University, USA.
6. Roland Diehl, Max-Planck-Gesellschaft, Munich, Germany.
Funding sources
We have support from a FAPESP Theme Project subvention and a grant from the National Institute of Quantum Science and Information Technology. Professor Mahir Hussein is coordinator of the Theme Project and the leading scholar of the second grant. Funding will also come from a FAPESP CEPID Project subsidy, currently being signed, with an 11-year duration. Professor Hussein is one of four main scholars of this project, which is coordinated by Professor Vanderlei S. Bagnato from IFUSP-São Carlos.