The shadow of a cosmic water cloud reveals the temperature of the young universe
A telescope in the French Alps has allowed researchers to peer deep into the past of the universe. For the first time, they were able to observe an extremely distant hydrogen cloud that shadows the cosmic background radiation created shortly after the Big Bang. The shadow is created because the colder water absorbs the warmer background radiation on its way to Earth. This provides information about the temperature of the cosmos just 880 million years after the Big Bang. To measure the early history of the universe, an international team used the Northern Extended Millimeter Array (NOEMA), the most powerful radio telescope in the northern hemisphere.
The universe came into being around 13.8 billion years ago with the Big Bang. At that time, a hot, dense fog of radiation and elementary particles wafted in space, which was rapidly expanding. The density and temperature decreased just as quickly, and the light particles (photons) lost increasingly more energy. After about 380,000 years, this plasma had cooled down to 3000 Kelvin. It was then possible for stable atoms to be created. And the photons had a free path and spread out into space. The cosmos became transparent so to speak.