The Low Frequency Array (Lofar): A Radio Telescope Spanning Northern Europe

In the last decades, an overarching paradigm for the formation and evolution of structure in the Universe has emerged: the cold dark matter and dark energy model (LCDM). This is a refinement of the Big Bang theory, which proposes that matter in the Universe consists mostly of cold dark matter that interacts mainly through gravity. A recent modification of CDM is the addition of a dark energy component, L, that currently dominates the Universe’s energy density and accelerates its expansion. According to the LCDM paradigm, very early, tiny density fluctuations in an otherwise homogeneous and isotropic Universe took 13.7 billion years to grow into the highly complex cosmos that we observe today.

The first stars and galaxies in the Universe start forming about 400 million years after the Big Bang. These objects emit ionizing radiation that ionizes and heats their surrounding. When a sufficient number of radiating objects have formed, the temperature and the ionized fraction of the gas in the Universe increased rapidly and most of the neutral hydrogen eventually ionize. This period, in which the cosmic gas went from being almost completely neutral to almost completely ionize, is known as the Epoch of Reionization (hereafter EoR).

The EoR was a watershed epoch in the history of the Universe. Prior to it, dark matter dominated the formation and evolution of structure while normal matter played a marginal role. After the EoR, the role of cosmic gas in the formation and evolution of structure became prominent and, on small scales, even dominant. Studies of this crucial epoch touch upon fundamental questions in cosmology, galaxy assembly, and formation of quasars and first stars. Much theoretical effort is currently dedicated to understand the physical processes that triggered and governed the evolution of this epoch, and their ramifications for subsequent structure formation.

Radiation emitted from neutral hydrogen in radio-wave regime during this epoch is the most promising probe for exploring the EoR. To date there are a number of low frequency radio telescope that are aiming at detecting this radiation.  The LOw Frequency ARray, LOFAR, which is a European telescope centered in the Netherlands, has started collecting data on December 2012. In this talk I will discuss the various scientific, computaional and technical challenges that our experiment faces, and present its current status and main results.