Born 13.4 billion years ago

Scientists have witnessed the formation of the first galaxies in our universe for the first time. They used the James Webb telescope for this. The birth of these three galaxies took place 13.3 to 13.4 billion years ago in a very young universe. To put it in perspective: our universe is 13.8 billion years old.

Shortly after the Big Bang, the universe consisted of hot plasma and there was no light yet. This plasma slowly cooled, after which electrons and protons formed hydrogen atoms. The first stars emerged 250 to 350 million years after the Big Bang, although these were extremely massive stars that lived only a few million years. The energy of these stars ionized hydrogen gas and made the universe transparent. Astronomers call this period the epoch of reionization. Shortly afterwards – about 13.4 to 13.5 billion years ago – more and more stars and galaxies emerged, such as the three galaxies-in-the-making that have now been spotted by James Webb.

The Danish scientists saw how large amounts of gas accumulated in small galaxies-in-the-making. It is the first time that they have observed this directly. Of course, there are many theories and computer simulations about the formation of galaxies, but never before has it been observed as clearly as it is now. Thanks to the discovery, these models can be compared with ‘real’ very young galaxies, allowing scientists to further refine these computer simulations.

“These are the first direct images of the formation of the very first galaxies,” says Assistant Professor Kasper Elm Heintz of the Niels Bohr Institute. “Thanks to James Webb, galaxies have been observed at other stages of evolution, but now we are witnessing the birth of the very first galaxies.” According to the researchers, the three galaxies formed 400 to 600 million years after the Big Bang.

Artist’s impression of these galaxies-in-the-making.

Gas clouds loom in infrared
James Webb is an infrared telescope, allowing scientists to look deeper into the universe. Infrared radiation penetrates through dust clouds, while visible light is blocked by dust clouds. In addition, the light from distant objects shifts to the infrared region, which is also called redshift, and James Webb can capture this light. Finally, infrared radiation is ideal for detecting cooler objects. In the case of the three galaxies-in-the-making, scientists spotted cold, neutral gas clouds. These were the building blocks of the first galaxies. They looked specifically at how light from these galaxies was absorbed by the neutral gas in the nearby environment. This transition is also called the Lyman-alpha transition by scientists.

Even further back in time?
The research team hopes that these discoveries will lead to new discoveries. “Maybe we can go back even further,” says PhD student Simone Vejlgaard of the Niels Bohr Institute. “One of life’s biggest questions is: where do we come from? Thanks to discoveries like this, we learn how the first structures in the universe emerged and we can further complete the puzzle,” adds Assistant Professor Gabriel Brammer.