03/27 09:48
There was a time when our universe was nothing but a dark and light sea of swirling gases, and by the time the universe was a billion years old, all of that had changed.
Radiation from the first stars and galaxies drastically changed, allowing light to flow freely across the entire electromagnetic spectrum.
A new simulation, named Thesan after the Etruscan goddess of dawn, allowed scientists to probe the dark ages of the universe. It’s a new tool to learn in detail how to turn on the lights in Cosmic Dawn.
“Thesan serves as a bridge to the early universe,” said physicist Aaron Smith of the Kavli Institute for Astrophysics and Space Research at MIT. “It should serve as an ideal simulated counterpart for upcoming observing facilities, which are poised to fundamentally change our understanding of the universe.” Most of what we know about the universe, we learn 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, this causes some problems; Just look (or don’t, as the case may be) at black holes, which don’t emit any detectable 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 dark hot mist of ionized gas. And the light was not able to travel freely through this mist; They simply scatter free electrons.
Once the universe had cooled enough, the protons and electrons began to recombine to form neutral hydrogen atoms. This means that light can finally travel through space. When the first stars and galaxies began to form, about 150 million years after the Big Bang, their ultraviolet light re-ionized neutral hydrogen everywhere in the universe, allowing the entire spectrum of electromagnetic radiation to flow freely. This is the era of reionization.
About a billion years after the Big Bang, the entire universe has been reionized; Before this billion-year mark, however, we can’t really see with our current tools, which makes it difficult to understand this crucial cosmic dawn.
Astrophysicist Rahul Kanan, of the Harvard-Smithsonian Center for Astrophysics, said: “Most astronomers don’t have laboratories to conduct experiments in. Space and time scales are very large, so the only way we can do experiments is on computers. We are able to take equations The basic physics and the governing theoretical models for simulating what happened in the early universe.”
The resulting simulation is the most detailed presentation yet of the era of reionization, the researchers said, capturing physics at scales a million times smaller than the simulated regions. This gives an “unprecedented” look at the way early galaxies formed and interacted with the gases of the early universe. It shows a gradual change as light begins to seep through the universe.
Interestingly, Thesan showed that initially light does not travel far at all. Only at the end of reionization is light able to travel long distances. The team also saw the types of galaxies that had the most influence on reionization, with galactic mass playing a large role.
And we won’t have long to wait to see how accurate the simulation is either. The James Webb Space Telescope (JWST) is due to begin science operations in a few months and is designed in part to go back nearly 300,000 years after the Big Bang, when reionization was in full swing.
The research was published in the Monthly Notices of the Royal Astronomical Society.