Astrophysics – Cosmology
The Institute of Nuclear Physics is active in Theoretical and Experimental Astrophysics and Cosmology research. This research activity includes:
Studies of topological formations in field theory and Cosmology of the Primordial Universe as well as studies on subjects in Particle Cosmology (such as Cosmological Phase Transitions, Inflationary and Accelerating Universe etc)
Measurements of cross sections (i.e. probabilities) of nuclear reactions which influence the nucleosynthesis process at various stages of star formation.
Energy production in the Stars
One of the big successes of Nuclear Physics is the solution of the mystery of the energy source in the stars. The initial explanation, that gravity compression is the source of heat emitted by the stars, would deplete their energy potential too fast. The problem was solved by the idea that, as temperature and pressure rise by the gravity compression, Nuclear Reactions become possible. The energy liberated balances the gravity and prolongues the life of the star. When finally the “fuel” is exhausted the star, either collapses or explodes, releasing large amounts of energy and the products of the nuclear reactions as Interstellar Matter.
Nucleosynthesis
The synthesis of the chemical elements (nucleosynthesis) takes place in the interior of stars that have been formed as a result of the “condensation of the interstellar gas and dust”. When the interior of the star, consisting mainly of Hydrogen, sufficiently contracts Hydrogen fusion begins, forming Helium. The ‘burning’ and formation of heavier elements up to Iron follows. If the mass of the star is at least eight times larger than the Solar mass then the star will “die” by a spectacular explosion (Supernova) during which a series of nuclear reactions occur producing all the elements heavier than Iron. The probability that these reactions occur forms the subject of research at the Institute of Nuclear Physics. For this purpose we perform a series of systematic measurements of reaction cross sections. The results are useful for the understanding of the mechanisms of heavy element nucleosynthesis and are widely used by astrophysicists to check and improve the models of “explosive nucleosynthesis” in order to perform realistic calculations of elemental abundances.
General Relativity
(i) Study of mathematical problems in classical General Relativity: exact solutions, equivalent systems of equations, integrability conditions, etc. We are currently focusing our efforts on time-dependent problems that allow emission of gravitational radiation, such as the collision of two point masses (black holes).
(ii) Development of software, based on MATHEMATICA, for carrying out mathematical calculations on a computer. Due to the complexity of the systems of equations considered in (i) the use of a computer is indispensable. The software is available on the internet. More details can be found here
http://www.inp.demokritos.gr/~sbonano/EDC/
http://www.inp.demokritos.gr/~sbonano/RGTC/
Astroparticle Physics
The standard model of strong and electroweak interactions along with the
theories of supersymmetry, supergravity and superstrings offer a detailed
microphysical picture over a vast range of distances and energies which span
from the size of the proton (10-13cm) down to the Planck scale (10-33
cm). In the standard cosmological picture of the Hot Big Bang the universe
starts out hot, dense and miniscule. It subsequently expands and cools down
homogeneously and isotropically.
The study of the very large in Cosmology and astrophysics and the very small in elementary particle physics has created the very fruitful new domain in theoretical and experimental research of Astroparticle Physics. Cosmological Observations offer useful probes and constraints to the arbitrary and undetermined microphysical parameters of particle physics. In turn the later provide new microscopic dynamical solutions to longstanding puzzles and determination of parameters of our Standard Cosmological Big Bang Model.