The James Webb Telescope Just Opened a Window to a Key Moment in the History of the Universe: The Birth of the First Galaxies

Three galaxies that formed less than 600 million years after the Big Bang tell the story of the first light of the cosmos.

Illustration of the cloud of gas that formed the first galaxies
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Pablo Martínez-Juarez

Since its launch two years ago, the James Webb Space Telescope has been our best resource for observing the primordial universe. With its ability to see further into the distance, this tool has allowed us to discover the oldest galaxies ever known.

Its latest discovery is nothing short of remarkable.

Triple birth. For the first time, a team of astronomers believes that they saw the birth of three galaxies at the dawn of our universe, in a period known as the era of reionization. This observation was possible because of the James Webb, which was designed with these kinds of tasks in mind.

A young universe. These galaxies would have formed more than 13 billion years ago, between 400 and 600 million years after the Big Bang, when the universe was only 3% of its current age.

Although this isn't the first time that the James Webb peers into this era of our cosmos, it could be the first time that we see the “awakening” of a galaxy in this primordial universe. A key event, as the era of reionization is precisely when light first appeared.

Reionization. We associate the Big Bang with a great explosion and, therefore, with a flash of light. The problem is that the universe was too dense for photons to move. When the universe ceased to be so dense, the “explosion” was no longer as forceful and the only thing that had formed was stable hydrogen.

“These galaxies are like sparkling islands in a sea of otherwise neutral, opaque gas,” explained Kasper Heintz, lead author of the study, in a press release. It was when this gas began to accumulate and form stars that light was made in the universe.

A time machine. The study is based on data compiled by the James Webb with its Near-Infrared Spectrograph (NIRSpec). The team used something known as the Lyman-alpha transition (Lyman-α) for their analysis. This transition occurs with the absorption of light by clouds of neutral gas surrounding the emission source.

This made it possible to distinguish the background gas from the newly formed galaxies. The details of the study were recently published in Science.

Not done yet. The team is cautious when it comes to interpreting the data. Some key points remain to be clarified, such as the relative location of the gas with respect to these early galaxies, or whether this gas is “pure hydrogen” or if heavier elements already existed back then.

There is still much work ahead. The team explains that the first step will be to search for more similar observations, in order to build a database that allows statistically sound conclusions; this will make it possible to validate the discovery, opening a new path in the exploration of the early history of our universe.

Image | Illustration of the cloud of gas that formed the first galaxies. NASA, ESA, CSA, Joseph Olmsted (STScI)

Related | Stephen Hawking Fell Short in His Prediction: The Universe Is Doomed To Evaporate

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