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"The Missing Baryons Hunt"
Dr. Fabrizio Nicastro
(1) Istituto Nazionale di Astrofisica - Osservatorio Astronomico di  Roma,  Italy
(2) Harvard-Smithsonian Center for Astrophysics, USA


When:  Friday 9 November 2007 at 12:00pm
Where: 2nd Floor Seminar Room

Abstract:

Despite recent progress in cosmology in assaying the composition of  
the energy-mass budget of the Universe, within the framework of our  
Standard Cosmological Model (SCM), very little is still known about  
nature and origin of 95 % of these constituents:  "dark" Energy and  
"dark" Matter. These have the name "dark" mainly to label our  
inability to directly detect and identify them. Less well known is  
that the situation is only conceptually better for the remaining 5 %  
of Omega: these are baryons, i.e. the constituents of  the ordinary  
matter of which stars, planets, and ourselves are made. Today we can  
account for less than 50% of the baryons that the SCM predicts,  
implying that at least 50 % of the baryons are now "missing".   
Finding and counting these baryons is therefore vital to our  
understanding of the Universe, and a necessary condition to validate  
the SCM. After a brief introduction of the problem, I will review all
the  different and independent pieces of evidence for these baryons,
and  will show that the majority of them is indeed still missing. In the
second part of my talk I will then try to identify new promising  
lines of research, which will hopefully allow us in the near future  
to hone our techniques of hunt and to converge toward a possible  
solution of this important and still open astrophysical problem.


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