The unanswered questions of our existence in this universe, and how this universe actually came into being, and how the galaxies evolve over time- these questions have been puzzling, to say the least.
We are far away from reaching a conclusion pertaining to these queries. However, we may be a step closer to unraveling these mysteries as the University of Arizona-led team of scientists has come up with new supercomputer simulations. Peter Behroozi, an assistant professor at the US Steward Observatory, was able to generate millions of different universes on a supercomputer.
The findings were published in the Monthly Notices of the Royal Astronomical Society, and it challenges the existing theories available on the formation of galaxies.
The computer, we can create many different universes and compare them to the actual one, and that lets us infer which rules lead to the one we see. - Behroozi
The simulated universes are the exact replicas of the real one, and the simulation contains 12 million galaxies spanning the time from 400 million years after the Big Bang to the present day. Each of the simulated universes went through a series of tests to evaluate how closely they came to the actual universe.
The researchers are calling it the “UniverseMachine” and it helped to resolve the question of why galaxies cease to form new stars even when they reteam plenty of hydrogen gas. Behroozi said, “As we go back earlier and earlier in the universe, we would expect the dark matter to be denser, and therefore the gas to be getting hotter and hotter. This is bad for star formation, so we had thought that many galaxies in the early universe should have stopped forming stars a long time ago. But we found the opposite: galaxies of a given size were more likely to form stars at a higher rate, contrary to the expectation.”
Behroozi and his team created virtual universes in which the galaxies kept forming new stars for much longer, contradicting the available theories. If the researches created the universe based on current theories in which the galaxies stopped forming stars early on, those galaxies appeared redder than the galaxies that we see in the sky.
According to the study, this is not the case. Behroozi explained, “But we don't see that. If galaxies behaved as we thought and stopped forming stars earlier, our actual universe would be colored all wrong. In other words, we are forced to conclude that galaxies formed stars more efficiently in the early times than we thought. And what this tells us is that the energy created by supermassive black holes and exploding stars is less efficient at stifling star formation than our theories unanswered predicted.”
If galaxies behaved as we thought and stopped forming stars earlier, our actual universe would be colored all wrong. In other words, we are forced to conclude that galaxies formed stars more efficiently in the early times than we thought. And what this tells us is that the energy created by supermassive black holes and exploding stars is less efficient at stifling star formation than our theories predicted.”
Creating the simulation was a challenge for the team as explained by Behroozi, “Simulating a single galaxy requires 10 to the 48th computing operations," he explained. "All computers on Earth combined could not do this in a hundred years. So to simulate a single galaxy, let alone 12 million, we had to do this differently.”
The team used the help of NASA Ames Research Center and the Leibniz-Rechenzentrum in Garching, Germany, and the "Ocelote" supercomputer at the UA High-Performance Computing cluster. Two-thousand processors crunched the data simultaneously over three weeks. Behroozi and his team generated more than 8 million universes. “We took the past 20 years of astronomical observations and compared them to the millions of mock universes we generated,” Behroozi explained, “we pieced together thousands of pieces of information to see which ones matched. Did the universe we created look right? If not, we'd go back and make modifications, and check again.”
Behroozi and his team want to extend the Virtual Universe Machine to include the morphology of individual galaxies and observe how their shapes evolve over time.