400 00 years after the Big Bang, matter cooled, and the Universe is filled almost of neutral hydrogen atoms. This first phase, called "dark age" lasts several hundreds of millions of years. It is gradually ended when the first stars and galaxies formed and, according to several models, the hydrogen atoms of the intergalactic medium are ionized by the strong ultraviolet emission of the first generation of stars, called Population III, extremely massive stars (several tens of solar masses). The epoch of reionization of the Universe begins.
An alternative scenario highlighting the role of the first stellar black holes has been proposed by an international team led by Felix Mirabel from the Service d’Astrophysique of CEA-Irfu.
Based on theoretical models and observations on the formation and evolution of primitive stars, scientists conclude that a significant fraction of them may lead to the formation of binary systems formed by a massive star and a black hole. In such system, material drawn by the compact star produces a very intense X-ray flux and relativistic particles (microquasars). Particles and photons will then ionize the surrounding medium and this over a long distance (provided that the medium is not too dense which is the case here). Indeed, their energy can ionize a quantity of atoms much greater than the UV radiation of stars, thus effectively irradiating the intergalactic medium. Calculations show that the density of these systems is sufficient to contribute significantly to the phase of reionization. Another important consequence of the proposed scenario is that these binary systems are also a major ingredient of the warming of the intergalactic medium.
Stellar black holes appear so to be essential elements to explain the early stages of the Universe.
Publication:
« Stellar black holes at the dawn of the universe »
I.F. Mirabel(1), M. Dijkstra(2,3), P. Laurent(1), A. Loeb(2) and J.R. Pritchard(2)
(1) CEA-Saclay, (2) Université de Harvard, USA, (3) Institut Max-Planck, Allemagne
To appear in Astronomy and Astrophysics (download pdf format, 180 Kb)
See also : « A smoother end to the dark ages » in News and Views, Nature, 7 April 2011 (pdf format, 950 Ko)
Contact:
Felix Mirabel
