Studying the universe is hard. Really hard. Like insanely, ridiculously hard. Think of the hardest thing you’ve ever done in your life, because studying the universe is quite literally exponentially way harder than whatever you came up with. Studying the universe is hard for two reasons: space and time. When we look at an object in the night sky, we’re looking back in time, as it has taken a finite amount of time for the light from that object to reach your eyes. The star Sirius is one of the brightest objects in the night sky and is located approximately 8.6 light-years from Earth. This means that when you look at it, you’re seeing what it looked like 8.6 years ago, as the speed of light is finite at 186,000 miles per second and a light year is the time it takes for light to travel in one year. Now think of something way farther away than Sirius, like the Big Bang, which supposedly took place 13.8 billion years ago. This means when scientists study the Big Bang, they’re attempting to look back in time 13.8 billion years. Even with all our advanced scientific instruments, it’s extremely hard to look back that far in time. It’s so hard that the Hubble Space Telescope has been in space since 1990 and just recently spotted the most distant single star ever detected in outer space at 12.9 billion light-years away. That’s 30 years of scanning the heavens, which is a testament to the vastness of the universe, and hence why studying the universe is hard. Because studying the universe is so hard, scientists often turn to computer simulations, or models, to help speed up the science aspect and ultimately give us a better understanding of how the universe works without waiting 30 years for the next big discovery.
In a recent study published in Nature Astronomy, researchers have created simulations that directly recreate the full life cycle of some of the largest collections of galaxies observed in the distant universe 11 billion years ago. This is the first time a study of this type has been conducted.
Cosmological simulations are crucial to studying how the universe became the shape it is today, but many do not typically match what astronomers observe through telescopes. Most are designed to match the real universe only in a statistical sense. Constrained cosmological simulations, on the other hand, are designed to directly reproduce the structures we actually observe in the universe. However, most existing simulations of this kind have been applied to our local universe, meaning close to Earth, but never for observations of the distant universe.
A team of researchers, led by Kavli Institute for the Physics and Mathematics of the Universe Project Researcher and first author Metin Ata and Project Assistant Professor Khee-Gan Lee, were interested in distant structures like massive galaxy protoclusters, which are ancestors of present-day galaxy clusters before they could clump under their own gravity. They found current studies of distant protoclusters were sometimes oversimplified, meaning they were done with simple models and not simulations.
“We wanted to try developing a full simulation of the real distant universe to see how structures started out and how they ended,” said Ata. Their result was COSTCO (COnstrained Simulations of The COsmos Field).
Lee said developing the simulation was much like building a time machine. Because light from the distant universe is only reaching Earth now, the galaxies telescopes observe today are a snapshot of the past.
“It’s like finding an old black-and-white picture of your grandfather and creating a video of his life,” he said.
In this sense, the researchers took snapshots of “young” grandparent galaxies in the universe and then fast forwarded their age to study how clusters of galaxies would form. The light from galaxies the researchers used traveled 11 billion light-years to reach us, meaning we are seeing how they looked 11 billion years ago.
“This is something that is very important for the fate of those structures whether they are isolated or associated with a bigger structure. If you don’t take the environment into account, then you get completely different answers. We were able to take the large-scale environment into account consistently because we have a full simulation, and that’s why our prediction is more stable,” said Ata.
Another important reason why the researchers created these simulations was to test the standard model of cosmology, that is used to describe the physics of the universe. By predicting the final mass and final distribution of structures in each space, researchers could unveil previously undetected discrepancies in our current understanding of the universe.
Using their simulations, the researchers were able to find evidence of three already published galaxy protoclusters and disfavor one structure. On top of that, they were able to identify five more structures that consistently formed in their simulations. This includes the Hyperion proto-supercluster, the largest and earliest proto-supercluster known today that is 5000 times the mass of our Milky Way galaxy, which the researchers found out it will collapse into a large 300 million light year filament.
Their work is already being applied to other projects including those to study the cosmological environment of galaxies, and absorption lines of distant quasars to name a few.
Cosmology is a branch of astronomy that involves the origin and evolution of the universe, from the Big Bang to today and on into the future. Cosmologists look at the entire universe from birth to death, as opposed to each component like individual stars and galaxies. A planetary scientist might study a small portion of the crust of a pie, while cosmologists study the entire pie all at once. Anytime you hear something about string theory, dark matter, dark energy, or the possibility of a multiverse, that’s cosmology. It’s responsible for answering the big questions such as how everything got here and where it’s going?
What new discoveries will cosmologists make about the history and future of the universe? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!