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[Galaxies et Cosmologie - Laboratoire LAGRANGE] Relativistic Astrophysics
Relativistic Astrophysics

The discovery of the acceleration of the expansion of the universe dates from the past ten years. The component responsible for such acceleration is dubbed "dark energy", whose nature remains a mystery and a challenge for physicists

In order to have a better insight about this mysterious and dominant component of the universe, our team investigates its effects at different scales. At the solar system scale, the dark energy affects the dimension of planetary orbits and introduces an extra source of precession, but unfortunately these effects are presently undetectable. The dynamics of groups of galaxies are also affected by the dark energy. This subject is being investigated by our team, in particular the dynamics of groups located in our vicinity (3-6 Mpc) since here measurable effects are expected.

If the dark energy is in fact associated to the so-called "cosmological constant" its effect,i.e., the acceleration of the expansion, is expected to disappear beyond z 0.6-0.7. Thus, it is of fundamental importance to check if acceleration is still present in past or, equivalently, when it appears. For this, a natural cosmological probe seems to be the gamma ray bursts (GRBs) already detected up to z 5. Our present investigations in this domain concern the analysis of the different distance indicators proposed for GRBs: can they be calibrated independently of the cosmology? Can these objects be used as standard candles? Could we have a better description of the dynamics of the universe combining the information carried by GRBs and distant (type Ia) supernovae?

Our team studies also other specific aspects related to Cosmology. In particular, alternative gravitation theories like the tensor-scalar and those implying extra-dimensions. Besides Cosmology, these theories will find an application in the study of the physics of compact objects and how their properties as gravitational wave sources will eventually be modified, aiming the computation of the astrophysical background.

 
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Friday 19 November 2010
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