(ORDO NEWS) — There was a time when our universe was nothing more than an opaque, lightless sea of bubbling gas.
However, by the time the universe was a billion years old, everything had changed. The radiation from the first stars and galaxies caused dramatic changes, allowing light to flow freely across the entire electromagnetic spectrum.
The new simulation, named Tesan after the Etruscan goddess of the dawn, has allowed scientists to explore the Dark Ages of the universe. This is a new tool for seeing in detail how the light could have come on.
Most of what we know about the universe we have learned from light (with the notable exception of gravitational waves, a field of astronomy still in its infancy). So, when the light is obstructed in some way, it causes quite a few problems; just look (or don’t look, as the case may be) at black holes that emit no discernible radiation.
The early universe between 50 million and 1 billion years after the Big Bang is another such case. This period is known as the Cosmic Dawn, a time when the Universe as we know it today was just beginning to assemble from primordial plasma.
Before the first stars appeared, it was filled with a hot, hazy haze of ionized gas. Light could not freely pass through this fog; it simply scattered free electrons.
Once the universe cooled down enough, protons and electrons began to recombine into neutral hydrogen atoms. This meant that light could finally travel through space.
When the first stars and galaxies began to form about 150 million years after the Big Bang, their ultraviolet light gradually re-ionized the neutral hydrogen ubiquitous in the universe, allowing the entire spectrum of electromagnetic radiation to circulate freely. This is the era of reionization.
About 1 billion years after the Big Bang, the universe was completely reionized; However, before this 1 billion year mark, we cannot see with our current instruments, making it difficult to understand the critical Cosmic Dawn.
Tesan starts with a realistic model of galaxy formation, as well as a new algorithm for reproducing how light interacts with and reionizes surrounding gas, as well as a model of cosmic dust.
These processes and interactions are very complex; to model a portion of the universe 300 million light-years in diameter, 400,000 to a billion years after the Big Bang, the team used the powerful SuperMUC-NG supercomputer, which used the equivalent of 30 million CPU hours to run Thesan.
According to the researchers, the resulting simulation is the most detailed representation of the epoch of reionization, reflecting physics on a scale a million times smaller than the regions being modeled.
This provides an “unprecedented” look at how early galaxies formed and interacted with the gas of the early universe. It shows a gradual change as light begins to seep through the universe.
Interestingly, Tesan showed that initially light does not travel very far at all. Only towards the end of reionization can light travel long distances. The team also saw which types of galaxies had the biggest impact on reionization, with galactic mass playing a big role.
We also won’t have to wait long to find out how accurate the simulation is. The James Webb Space Telescope (JWST) is due to start scientific work in a few months and is designed in part to look back about 300,000 years after the Big Bang, when reionization was in full swing.
In any case, we will learn something very interesting about the mysterious birth and early years of our amazing universe.
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