Archive for October 18, 2011

Next Step in Design of LAGUNA Neutrino Observatory

October 18, 2011 Leave a comment

The kick-off meeting for the second phase of the LAGUNA’s design study starts today at CERN. The principal goal of LAGUNA (Large Apparatus for Grand Unification and Neutrino Astrophysics) is to assess the feasibility of a new pan-European research infrastructure able to host the next generation, very large volume, deep underground neutrino observatory. The scientific goals of such an observatory combine exciting neutrino astrophysics with research addressing several fundamental questions such as proton decay and the existence of a new source of matter-antimatter asymmetry in Nature, in order to explain why our Universe contains only matter and not equal amounts of matter and antimatter.

Underground neutrino detectors based on large, surface-instrumented, liquid volumes have achieved fundamental results in particle and astroparticle physics, and were able to simultaneously collect events from several different cosmic sources. Neutrinos interact only very weakly with matter so they can travel very large distances in space and traverse dense zones of the Universe, thus providing unique information on their sources and an extremely rich physics programme.

In order to move forward, a next-generation very large multipurpose underground neutrino observatory of a total mass of around 100 000 to 500 000 tons is needed. This new facility will provide new and unique scientific opportunities, very likely leading to fundamental discoveries and attracting interest from scientists worldwide.

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How the Milky Way Killed Off Its Satellites

October 18, 2011 Leave a comment

Two researchers from Observatoire Astronomique de Strasbourg have revealed for the first time the existence of a new signature of the birth of our galaxy’s first stars. More than 12 billion years ago, their intense light dispersed the gas of the Milky Way’s satellite galaxies. By computing the observable consequences of this process, Pierre Ocvirk and Dominique Aubert demonstrated their prevailing role. This result confirms that reionisation is indeed an essential process in the standard model of galaxy formation. The study took place within the LIDAU collaboration (Light In the Dark Ages of the Universe). It is published in the october issue of the letters of the Monthly Notices of the Royal Astronomical Society.

The first stars of the Universe appeared about 150 million years after the Big Bang. Back then, the hydrogen and helium gas filling the universe was cold enough to have its atoms be electrically neutral. As the intense light of the first stars propagated through this gas, it broke the hydrogen atoms, returning them to the plasma state they experienced in the first moments of the Universe. This process, known as reionisation, also results in significant heating, which can have dramatic consequences: the gas becomes so hot that it escapes the weak gravity of the lowest mass galaxies, thereby depriving them of the material needed to form stars. It is now widely admitted that this photo-evaporation process explains the small number and large ages of the stars seen in the dwarf galaxies satellites of the Milky Way. It also offers a credible solution to the missing satellites problem. On the other hand, their sensitivity to UV radiation means satellite galaxies are good probes of the reionisation epoch. Moreover, they are relatively nearby, from 30000 to 900000 light-years, which allows us to study them in great details, especially with the forthcoming generation of telescopes. In particular, the study of their stellar content with respect to their position could give us precious insight into the structure of the local UV radiation field during the reionisation epoch.

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