Temperatures and pressures were so high for the first 300,000 years of the Universe, according to Big Bang theory, that atoms could not exist. Instead, the matter was spread as a highly ionized plasma that was extremely effective at scattering radiation. As a result, information (photons) from the early Universe were effectively imprisoned in an impenetrable ‘fog,’ which still conceals these early times from scientists today.
Astronomers have discovered a novel method for estimating the temperature of the cosmic microwave background when the Universe was still in its infancy. They corroborate the early cooling of our Universe immediately after the Big Bang in their new study and shed new light on the enigmatic dark energy.
An international team of physicists has developed a new approach for estimating the cosmic microwave background temperature of the young Universe, only 880 million years after the Big Bang. It is the first time that the temperature of cosmic microwave background radiation, a relic of the energy generated by the Big Bang, has been measured at such an early epoch of the Universe.
The dominant cosmological model assumes that the Universe has cooled since the Big Bang – and that it is continuously cooling. The model also outlines how the cooling process should take place, but it has only been directly proven for very recent cosmic eras so far. The discovery not only marks an important step forward in the evolution of the cosmic background temperature, but it may also have ramifications for the elusive dark energy. Nature published the paper ‘Microwave background temperature at a redshift of 6.34 from H2O absorption.’
Our team is already following up with NOEMA by analyzing the environs of additional galaxies. It remains to be seen if our current, basic knowledge of the expansion of the Universe stands up with the projected increases in precision from investigations of larger samples of water clouds.
Dr. Roberto Neri
The scientists observed HFLS3, a large starburst galaxy at a distance equivalent to an age of barely 880 million years after the Big Bang, using the NOEMA (Northern Extended Millimeter Array) observatory in the French Alps, the most powerful radio telescope in the Northern Hemisphere. They found a cold water gas screen that casts a shadow on the cosmic microwave background radiation.
The shadow appears because the colder water absorbs the warmer microwave radiation on its path toward Earth, and its darkness reveals the temperature difference. As the temperature of the water can be determined from other observed properties of the starburst, the difference indicates the temperature of the Big Bang’s relic radiation, which at that time was about seven times higher than in the Universe today.
‘This result not only proves cooling, but it also demonstrates that the Universe in its early days had some fairly particular physical characteristics that no longer exist today,’ said lead author Professor Dr. Dominik Riechers of the University of Cologne’s Institute of Astrophysics. ‘The cosmic microwave background was already too cold for this impact to be observed quite early, about 1.5 billion years after the Big Bang. ‘As a result, we have a unique observational window that only opens up to a very early Universe,’ he concluded. In other words, if a galaxy with otherwise comparable features to HFLS3 existed today, the water shadow would no longer be visible since the needed temperature contrast would no longer exist.
‘This significant milestone not only confirms the expected cooling trend for a much earlier epoch than has previously been measured, but it may also have direct implications for the nature of the elusive dark energy,’ said co-author Dr. Axel Weiss of the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn. Dark energy is considered to be responsible for the Universe’s accelerated expansion during the last few billion years, but its features remain unknown because it cannot be directly examined with the current facilities and tools.
However, its features have an impact on the evolution of cosmic expansion and, as a result, the rate of cooling of the Universe throughout cosmic time. Based on this experiment, the qualities of dark energy are still consistent with Einstein’s ‘cosmological constant.’ ‘That is to say, an expanding Universe in which the density of dark energy remains constant,’ Weiss added.
The team has located one such cold water cloud in a starburst galaxy in the early Universe and is currently looking for many more across the sky. Their goal is to trace the cooling of the Big Bang echo across the first 1.5 billion years of cosmic history. ‘This new technique provides important new insights into the evolution of the Universe, which are very difficult to constrain otherwise at such early epochs,’ Riechers said.
‘Our team is already following up with NOEMA by analyzing the environs of additional galaxies,’ co-author and NOEMA project scientist Dr Roberto Neri stated. ‘It remains to be seen if our current, basic knowledge of the expansion of the Universe stands up with the projected increases in precision from investigations of larger samples of water clouds.’
