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Quark Matter and the cosmological QCD phase transition
At
temperatures above 100 MeV the baryons in our universe are no longer
in the form of bound objects, rather they undergo a phase transition to
a plasma of free quarks and gluons. This phase transition could have
extremely interesting consequences for a whole bunch of problems.
It could give rise to matter inhomogeneties resulting in a very different
nucleosynthesis outcome or it could possibly produce black holes in
abundance.
Presently there
are substantial experimental efforts to produce such a phase
transition in the laboratory by colliding heavy ions. This produces an
ultra-energetic plasma that may undergo a phase transition if its energy
is sufficient. Actually producing such a quark-gluon plasma in the
laboratory is bound to yield a lot of information about the strong
interaction and the cosmic QCD phase transition.
Neutrino Cosmology
The
standard big bang theory predicts that neutrinos are among the
most abundant particles in our universe and that they should therefore
be very important for the evolution of our universe. By now the neutrinos
should exist as a cosmic background radiation like the 2.7 K photon
background.
However,
since neutrinos are only weakly interacting there
is very little hope of ever detecting this background sea of neutrinos
directly. Neutrinos manifest themselves more dramatically in the early
universe, for instance they play a key role in the formation of light
nuclei during big bang nucleosynthesis. They are also very important for
the formation of structure in the universe.
Turning
the argument around,
cosmology can be used to constrain neutrino parameters; properties
that cannot be measured in the laboratory exactly because neutrinos
are so hard to detect.
High Redshift Galaxies and Quasar Absorption Line Systems
A very
promising and fruitful method by which to study how structure - in
particular galaxies - formed in the early high redshift universe is based
on the study of the spectra of the most distant and luminous objects in
the universe: quasars. Penetrated by thousands of lines of sights to
very distant quasars the universe resembles a pincushion with measuring
devices attached to each point on each needle. Each needle - or line of
sight as it is - tells its own story from when the universe was a few
percent of its present age until today.
In
one of the research projects at
IFA we study the relation between objects causing absorption in quasar
spectra and high redshift galaxies.
Emission Spectra of Extragalactic HII regions
To learn
how galaxies form and evolve, observations of chemical composition are important. Absorption lines in spectra
of single stars cannot be observed as in the Milky Way, but the abundances of the interstellar matter
can be found from emission spectra when ionized by very hot stars embedded in an HII region.
The observed spectra must be corrected for the extinction caused by interstellar dust grains.
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