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A team of astrophysicists has just created 8 million unique universes inside a supercomputer and let them evolve from mere toddlers to old geezers. Their objective? To define the role of an invisible substance called black matter played in the life of our universe since the Big Bang and what it means for our destiny.
After discover that our universe Made up mostly of dark matter in the late 1960s, scientists speculated on its role in forming galaxies and their ability to give birth to new stars over time.
According to The Big Bang Theory, shortly after the birth of the universe, an invisible and elusive substance that physicists have dubbed dark matter the force of gravity in massive clouds called dark matter halos. When the halos grew, they attracted the insufficient hydrogen gas that crossed the universe to gather and form the stars and galaxies today. In this theory, dark matter acts as the backbone of galaxies, dictating their formation, fusion and evolution over time.
Related: The 11 biggest unanswered questions about dark matter
To better understand how dark matter has shaped this story of the universe, Peter Behroozi, assistant professor of astronomy at the University of Arizona, and his team have created his own worlds in using the school's supercomputer. The 2,000 computer processors have been running continuously for three weeks to simulate more than 8 million unique universes. Each universe individually obeyed a unique set of rules to help researchers understand the relationship between dark matter and the evolution of galaxies.
"On the computer, we can create many different universes and compare them to the current universe, which allows us to deduce which rules lead to the one we see," said Behroozi. said in a statement.
While previous simulations have focused on modeling simple galaxies or creating fictitious universes with limited parameters, UniverseMachine is the first of its scope. The program has continuously created millions of universes, each containing 12 million galaxies, and each of them has been able to evolve over almost the entire history of the real world, from 400 million years after the Big Bang to our days.
"The big question is," How are galaxies formed? "Said Risa Wechsler, professor of physics and astrophysics at Stanford University. "What's really good in this study is that we can use all the data we have on the evolution of galaxies – the number of galaxies, their number of stars and their way of form these stars – and group them into a complete picture of the last 13 billion years of the universe. "
Related: From the big bang to the present: snapshots of our universe through time
Creating a replica of our universe, or even a galaxy, would require a quantity of inexplicable computing power. Thus, Behroozi and his colleagues focused their attention on two key properties of galaxies: their combined mass of stars and the speed at which they give rise to new ones.
"Simulating a single galaxy requires 10 to 48 computer operations," explained Behroozi, referring to an operation of an octillion, or a 1 followed by 48 zeros. "All combined computers on Earth could not do that in a century, so to simulate a single galaxy, let alone 12 million, we had to do it differently."
As the computer program creates new universes, it guesses how the star formation rate of a galaxy is related to its age, its past interactions with other galaxies and the amount of dark matter. in his halo. He then compares each universe with real observations, adjusting the physical parameters at each iteration to better correspond to reality. The end result is a universe almost identical to ours.
According to Wechsler, their results showed that the speed at which galaxies give rise to stars is closely related to the mass of their dark matter halos. Galaxies with dark matter halo masses very similar to our own Milky Way had the highest star formation rates. She explained that star formation is smothered in more massive galaxies by an abundance of black holes
Their observations also questioned long-held beliefs that dark matter stifled star formation in the early universe.
"Coming back to the universe earlier and earlier, we would expect the dark matter to be denser and therefore the gas to become hotter and warmer. We had thought that many early galaxies in the universe should have stopped forming stars for a long time, "said Behroozi. "But we found the opposite: galaxies of a given size were more likely to form stars at a higher rate, contrary to expectations."
The team is now planning to expand the UniverseMachine to test more ways by which dark matter could affect the properties of galaxies, including the evolution of their shapes, the mass of their holes black and the frequency of passage of their stars. supernova.
"For me, the most exciting thing is that we now have a model in which we can start asking all these questions in a framework that works," Wechsler said. "We have a fairly inexpensive computational model that allows us to essentially compute an entire universe in about one second, and then we can afford to do it millions of times and explore all the time. parameters space. "
The research group published its findings in the September issue of the journal Monthly Notices from the Royal Astronomical Society.
Originally published on Science live.
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