In this way, astronomers invented and tested one new theory of galaxy formation after another. Peter Behroozi, assistant professor of UA Steward Observatory, and the research team overcame this obstacle and generated millions of different universes on a supercomputer. Every universe follows different physical theories to explain how galaxies should form. The discovery, published in the Monthly Journal of the Royal Astronomical Society, challenges the basic view that dark matter plays a role in the formation of galaxies, how galaxies evolve over time and how stars are born.
Monica bellucci, the main author of this study, said: On the computer, many different universes can be created. By comparing the simulated universe with the actual universe, we can infer which laws created the real universe we see today. This study is the first self-consistent study to create the universe. These simulated universes are exact copies of the real universe:
Every computer simulation represents a considerable part of the real universe, including 654.38+02 million galaxies, with a time span from 400 million years after the Big Bang to today. Each simulated universe has undergone a series of tests to evaluate how similar galaxies in the simulated universe compare with the real universe.
The most similar simulated universe has similar basic physical laws, which provides a powerful new method for studying galaxy formation. The research results of "cosmic machine", as the author said, help to solve a long-standing paradox, that is, why galaxies stop forming new stars even if they retain a lot of hydrogen (the raw material for star formation). The general view on how galaxies form stars involves that cold gas collapses into dense small pieces under the action of gravity, which produces complex interactions between stars, while other processes offset the formation of stars.
For example, it is believed that there are supermassive black holes in the center of most galaxies, and the matter falling into these black holes will release huge energy, just like a cosmic blowtorch, preventing the gas from cooling enough to collapse into a star nursery. Similarly, stars that ended their lives in supernova explosions also participated in this process. Dark matter also plays an important role, because it provides most of the gravity acting on the visible matter in the galaxy, inhaling cold gas from around the galaxy and heating it in the process. As we return to the universe earlier and earlier, it is expected that the density of dark matter will become larger and larger, so the gas will become hotter and hotter.
This is not conducive to the formation of stars, so researchers believe that many galaxies in the early universe should have stopped forming stars long ago. But the opposite is found: galaxies of a certain size are more likely to form stars at a higher speed, which is contrary to expectations. In order to match the observations of actual galaxies, the research team must create an opposite virtual universe, in which galaxies continue to produce a large number of stars for a much longer period of time. On the other hand, if researchers create the universe according to the current theory of galaxy formation (galaxies in the universe stop forming stars in the early days), these galaxies look much redder than the galaxies that astronomers see in the sky.
Galaxies are red for two reasons. The first phenomenon is obvious in nature and is related to the age of galaxies. If galaxies were formed early in the history of the universe, they would move away from the earth at a faster speed and convert light into red spectrum. Astronomers call this effect redshift. Another reason is internal: if a galaxy has stopped forming stars, the number of blue stars in the galaxy will decrease, and blue stars usually die faster, leaving only older and redder stars.
But we don't see it that way. If galaxies behave as we think and stop forming stars earlier, the real universe will be "painted" with completely wrong colors. In other words, galaxies are more efficient than expected in forming stars in the early stage. This shows that the energy efficiency produced by supermassive black holes and exploding stars is lower than theoretical prediction. Therefore, creating an unprecedented complex simulated universe requires a new method, which is not limited by computing power and memory and provides sufficient resolution, from "small" objects (such as supernovae) to a considerable area in the Hubble volume.
Simulating a galaxy requires the calculation of 10 to the 48th power, which all computers on the earth can't do in a hundred years. So, it's just to simulate a galaxy, not to mention12 million galaxies, but in order to do this, we must use different methods. In addition to using the computing resources of Ames Research Center and Leibniz-Reichenz Center of NASA in Germany, the team also used the "Ocelote" supercomputer in the UA high-performance computing cluster. More than 2000 processors simultaneously process data in three weeks. In this research project, more than 8 million different simulated universes were created and simulated.
Scientists use the astronomical observation data of the past 20 years to compare the observation data with the millions of simulated universes created by simulation. Thousands of messages have been collected to see which one matches. Does the simulated universe look right? If it doesn't match, the researcher will go back and revise it and check it again until it matches. In order to further understand how galaxies are formed, the research team plans to expand the "cosmic machine" project, including the shape of a single galaxy and how its shape evolves over time.