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Astronomers simulate the early universe and the birth of the first galaxies

An international collaboration of astronomers has created the most detailed simulation yet of the early stages of the universe. The simulation can be seen in the video below, showing the first light spreading through the darkness in a period called the epoch of reionization, around 13 billion years ago.

Internal 3D view of the gas density evolution in Thesan-1

This is the period when hydrogen atoms became ionized and allowed light to spread through the universe, and the earliest galaxies formed. This period was chaotic and hard to model, which was the challenge taken up in creating this Thesan simulation which was developed by scientists at MIT, Harvard University, and the Max Planck Institute for Astrophysics.

 Still image from a Thesan simulation showing the universe 251 million years after the Big Bang. The orange halos represent the burst of radiation, or light, outpouring from early galaxies.
Still image from a Thesan simulation showing the universe 251 million years after the Big Bang. The orange halos represent the burst of radiation, or light, outpouring from early galaxies. Thesan Collaboration

“Most astronomers don’t have labs to conduct experiments in. The scales of space and time are too large, so the only way we can do experiments is on computers,” said author Rahul Kannan, an astrophysicist at the Center for Astrophysics at Harvard, in a statement. “We are able to take basic physics equations and governing theoretical models to simulate what happened in the early universe.”

The team created the most detailed simulation to date of what this period may have been like, covering an area of 300 million light-years and running through the first billion years after the Big Bang.

Because this happened so long ago, it is very difficult to observe evidence from this period. However, new telescopes like the James Webb Space Telescope (JWST) will be able to see very distant galaxies — and because light takes time to travel such distances, observing these galaxies is like looking back in time. Researchers are hopeful that these newer telescopes will be able to gather data that they can compare to their simulation.

“A lot of telescopes coming online, like the JWST, are specifically designed to study this epoch,” said Kannan. “That’s where our simulations come in; they are going to help us interpret real observations of this period and understand what we’re seeing.”

Being able to compare real data to the simulation could reveal more about this period. “And that’s the interesting part,” said co-author Mark Vogelsberger, an associate professor of physics at MIT. “Either our Thesan simulations and model will agree with what JWST finds, which would confirm our picture of the universe, or there will be a significant disagreement showing that our understanding of the early universe is wrong.”

The research is published in the journal Monthly Notices of the Royal Astronomical Society.

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