Séminaire / Seminar GReCO |
| « Modified Gravity in the Bullet Cluster » |
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B. Famaey |
| After summarizing the success and failure of the Cold Dark Matter paradigm on galaxy scales, we present its main phenomenological contender, known as MOND (Modified Newtonian Dynamics). We then present the weak lensing observations of 1E0657-56, an extremely interesting object, known as the bullet cluster, in which the collisionless component and the fluid-like X-ray emitting plasma are spatially segregated due to the collision of two galaxy clusters. We fit this lensing map in a class of gravity theories interpolating between General Relativity and MOND, so to infer the nature and amount of collisionless matter with less dependence on the validity of GR on cluster scales. We show that 1E0657-56 is dominated by a collisionless (most probably non-baryonic) component - in GR as well as in MOND. This result adds to the number of wrong MOND predictions based on observed baryons only on scales larger than galaxies (namely an inability in explaining dynamics of other X-ray emitting clusters and in fitting the CMB). A plausible resolution of these issues in MOND is its marriage with Hot Dark Matter made of ordinary neutrinos of maximum mass 2eV. |
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lundi 19 février 2007 - 11:00 Salle des séminaires Évry Schatzman Institut d'Astrophysique de Paris |
| Pages web du séminaire / Seminar's webpage |