Dark matter at the University of Bologna
Research into dark matter is carried out by the Astronomy and Physics Departments of the University of Bologna, in collaboration with the Astronomical Observatory of Bologna, national research organisations such as ASI (the Italian Space Agency ), CNR (National Research Council) and INFN (National Institute of Nuclear Physics) and international research organisations.
One of the most important proofs of the presence of dark matter in the spiral galaxies comes from the curves that describe the rotational speed of galactic matter as a function of the distance from the centre of the galaxy itself (see movement of stars in a galaxy). The curves are obtained from observations of spectral lines emitted by ionized gas (Alpha line), by neutral hydrogen gas (line at 21 cm wavelength) and by molecular gas (CO), measuring the displacement of the frequency of the line (due to the Doppler effect). While the ionized gas and the molecular gas are found in the brighter, central parts of the galaxies, neutral hydrogen extends well beyond the luminous disk. This allows us to trace the rotation curves at large distances from the centre of the galaxies.
The search for dark matter of an
type can be either direct or indirect. Direct experimental methods
are based on the possible interaction of dark matter particles inside a detector, or which crosses the detector.
Indirect studies try to detect, for example, neutrinos
generated in the decay of hadrons produced in particle-antiparticle
(of dark matter) which may occur at the centre of the Earth, the Sun or the Galaxy.
The Physics Department carries out dark matter
research through laboratory experiments without accelerators
AMS), and experiments with accelerators
Nuclearites would be objects like atomic nuclei, but containing stype quarks as well as u and d types found in ordinary matter. These quarks should be free to move around within a nuclearite, while being "confined" there. The nuclei of ordinary matter, instead, are formed of u and d type quarks which can move only inside a proton or a neutron. Neutralinos would be neutral
supersymmetric elementary particles; these could be one of the main components of dark matter. Neutralinos could collide with the atomic nuclei of a celestial body like the earth or the sun, and could remain trapped in their centre by the force of gravity. A neutralino and an antineutralino could annihilate, giving rise to pions and thus to muon neutrinos. MACRO looked for a flux of muon-neutrinos coming from the centre of the earth and the sun, setting important limits.
The supersymmetric particles which could make up part of the Universe's dark matter can be investigated with the following accelerator experiments:
A theory group, in collaboration with a group from the CNR of Bologna involved in the PLANCK experiment, is studying the implications of dark matter and dark energy with regard to the results of experiments on the microwave cosmic background radiation and its anisotropies .The experiments have provided detailed images of the Universe when it had a temperature of about 3000 degrees. The ever-improving precision and resolution with which these anisotropies are detected gives access to primordial information on the dark components of the Universe.