Centre National d'Etudes Spatiales (CNES)
Toulouse, France

Contact chercheur:
Alain Blanchard
Professeur UPS au Laboratoire d'Astrophysique (UMR 5572)
Observatoire Midi-Pyrénées
Tél: O5 61 33 28 42, e-mail:

Contact Presse:
Dominique D'Arabian
chargée de communication
Observatoire Midi-Pyrénées
Tel: 05 61 33 28 67, e-mail:

Contact Cnes:
Julien Guillaume
Tel: 01.44.76.76.83, e-mail:

PRESS RELEASE: November 20th, 2003

Does Vacuum Energy Really Dominate The Cosmos?

New results from a study of distant galaxy clusters, observed as they were when
the universe was only half as old as it is today, lead to some surprising
conclusions.

The observations were obtained by the European Space Agency's (ESA) satellite
XMM in the context of an international collaboration involving researchers from
two laboratories (the Laboratoire d'Astrophysique and the Centre d'Etude
Spatiale des Rayonnements (CESR) at the Observatoire Midi-Pyrénées (OMP ) in
Toulouse, the Institut d'Astrophysique Spatiale (IAS) in Paris, the Collège de
France, the Service d'Astrophysique (SAp) in Saclay, and the ESA center ESTEC in
Holland.

The scientific interpretation of these observations will soon appear as a letter
in Astronomy and Astrophysics. The observations indicate that the abundance of
X-ray luminous galaxy clusters was much lower at this ancient epoch, which
suggests that the matter density of the Universe is significantly larger than
what has been commonly assumed since the observations of the cosmic background
radiation reported by NASA's WMAP satellite.

This new result could call into question the need for vacuum energy!

In any case, the results indicate that certain basic assumptions adopted by
cosmologists will have to be modified: If galaxy clusters behave as commonly
assumed, then one must abandon the ideal of a universe dominated by vacuum
energy -- a radical change relative to recent ideas in the field; otherwise, one
will have to understand the physical processes operating to make galaxy clusters
more complicated objects than expected.

The French national space agency CNES provides funding for the XMM mission
through its contribution to ESA's obligatory science program and directly on the
national level via an important contribution to the financing of mission
instruments built by international consortia, such as the European Photon
Imaging Camera (EPIC, French Co-Is: CEA/Sap and IAS) and the EPIC Radiation
Monitor (ERM, French PI: CESR), and through its funding of data analysis managed
by the XMM Survey Science Centre (SSC, French Co-Is: Observatoire de Strasbourg,
CEA/Sap, CESR, OMP).

The CNRS is also associated to the XMM-Newton mission through his associated
laboratories : Laboratoire d'Astrophysique et Centre d'Etude Spatiale des
Rayonnements de Toulouse

(Observatoire Midi-Pyrénées et Université Paul Sabatier), Institut
d'Astrophysique Spatiale d'Orsay (Université d'Orsay), Observatoire de
Strasbourg (Université Louis Pasteur).