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2Physics Quote:
"Can photons in vacuum interact? The answer is not, since the vacuum is a linear medium where electromagnetic excitations and waves simply sum up, crossing themselves with no interaction. There exist a plenty of nonlinear media where the propagation features depend on the concentration of the waves or particles themselves. For example travelling photons in a nonlinear optical medium modify their structures during the propagation, attracting or repelling each other depending on the focusing or defocusing properties of the medium, and giving rise to self-sustained preserving profiles such as space and time solitons or rapidly rising fronts such as shock waves." -- Lorenzo Dominici, Mikhail Petrov, Michal Matuszewski, Dario Ballarini, Milena De Giorgi, David Colas, Emiliano Cancellieri, Blanca Silva Fernández, Alberto Bramati, Giuseppe Gigli, Alexei Kavokin, Fabrice Laussy, Daniele Sanvitto. (Read Full Article: "The Real-Space Collapse of a Two Dimensional Polariton Gas" )

Monday, May 08, 2006

Hydrogen in Far Galaxy

A team of astronomers from European Southern Observatory (ESO) detected the presence of molecular hydrogen in the farthest system ever, an otherwise invisible galaxy that we observe when the Universe was less than 1.5 billion years old (The universe is estimated to be about 15 billion years old). The astronomers find that there is about one hydrogen molecule for 250 hydrogen atoms. This also implies that the gas in this galaxy must be rather cold, about -90 to -180 degrees Celsius. In addition, several lines from 'metals' are also seen, allowing the researchers to deduce the amount of various chemical elements.

The team arrived at this conclusion analyzing light from a quasar located 12.3 billion light-years away. A similar set of observations for two other quasars, together with the most precise laboratory measurements, allows scientists to infer that the ratio of the proton to electron masses may have changed with time (our last posting).

These exciting results will be available in a paper accepted for publication in the Astrophysical Journal Letters ("Molecular Hydrogen in a Damped Lyman-╬▒ system at zabs=4.224", by C. Ledoux, P. Petitjean, and R. Srianand).

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