The post Big Bang revealed: A first step towards understanding the early Universe

After the Big Bang, the Universe expanded and, by cooling down, the matter progressively took shape. The first stars and galaxies form several hundred thousand years later. One billion year later the Universe is observed to be reheated, and hydrogen, the most abundant element, is again ionized, as it was shortly after the Big Bang. How has this important transformation, named cosmic reionization, been possible? Astronomers have long thought that galaxies were responsible for this phenomenon. Tod