Detection of the first galaxies in the Universe by the James Webb telescope

For the first time, astronomers using the James Webb Space Telescope (JWST) may have detected some of the universe’s earliest galaxies in the early stages of formation. A study reports the detection of what appear to be three nascent galaxies emerging from a primordial cloud of hydrogen and helium gas, just 400 to 600 million years after the Big Bang.

And there was light

The cosmos as we know it today was not always so clear and transparent. About 13.8 billion years ago, it was filled with dense, dark gas. This period, which immediately followed the big Bangis often called the cosmic dark age. During this epoch, the universe was in complete darkness, as the first stars had not yet begun to shine. It was composed mainly of hydrogen and helium, the simplest and most abundant elements formed during the Big Bang. About 400 million years after the Big Bang, a new crucial period, called theera of reionizationbegan. The first stars and galaxies began to form and shine. By emitting high-energy photons, they then began to ionize the surrounding gas, that is, to tear electrons from the hydrogen and helium atoms. This process of reionization gradually transformed the gas from neutral and opaque to an ionized and transparent state. Understanding this period of reionization is crucial for astronomers, because it marks the transition from the primordial, dark and dense universe to the structured and transparent universe that we observe todayhence the interest in this new discovery.

Spiral galaxy NGC 6744 observed by the Euclid telescope. Credits: ESA/Euclid/Euclid Consortium/NASA

The first galaxies of the universe

Astronomers have recently observed three nascent galaxies emerging from a primordial cloud of hydrogen and helium gas. These galaxies formed only 400 to 600 million years after the Big Bang. We owe this observation to the exceptional capabilities of the telescope James WebbEquipped with ultra-sensitive instruments, the latter is capable of detecting faint light signals from the beginnings of the universe. To analyze these galaxies, astronomers studied the light spectra, that is, the different colors of light they emit. They then discovered that the light from three of them was absorbed by large amounts of neutral hydrogen. This absorption indicates that these galaxies were using this gas to form new stars. In other words, these galaxies were in the process of transforming the surrounding gas into stars, a crucial process in the evolution of the universe. The discovery of these first galaxies by the James Webb telescope, reported in Sciencethus represents a major advance for astronomy, because it opens a unique window on the beginnings of the universe and helps us understand how our cosmos evolved. By observing these first galaxies, scientists can study how the first stars and galaxies helped to ionize the surrounding gas. This helps us understand how the universe became transparent, allowing light to travel freely through space. Future observations by JWST will confirm these findings and deepen our understanding of the beginnings of the universe.