Supercomputer delivers new Lyman Forest simulation suite to illustrate large-scale structure of universe

Like celestial beacons, distant quasars emit the brightest light in the universe. They emit more light than our entire galaxy. The light comes from matter torn apart as it is swallowed by a supermassive black hole. Cosmological parameters are important numerical constraints used by astronomers to track the evolution of the entire universe billions of years after the Big Bang.

Quasar light passes through huge clouds of neutral hydrogen gas 20 million light-years or more in diameter that formed shortly after the Big Bang, revealing clues about the large-scale structure of the universe.

The Texas Advanced Computing Center’s (TACC) Frontera supercomputer used quasar light data to help astronomers develop PRIYA, the largest fluid dynamics simulation suite to date for simulating large-scale structures in the universe.

“We created a new simulation model to compare with data that exists in the real universe,” said Simon Byrd, assistant professor of astronomy at the University of California, Riverside.

Bird and colleagues developed PRIYA, which acquires optical data from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the Sloan Digital Sky Survey (SDSS).He and colleagues published work announcing PRIYA in October 2023 Journal of Cosmology and Astroparticle Physics (JCAP).

“We compared the eBOSS data to various simulation models with different cosmological parameters and different initial conditions of the universe (such as different matter densities),” Bird explained. “You find the one that works best, and how far away from that method you can go without destroying reasonable consistency between the data and simulations. This knowledge tells us how much matter there is in the universe, or how much matter there is in the universe. How many structures there are. The universe.”

The PRIYA simulation suite is connected to a large-scale cosmological simulation also co-developed by Bird, called ASTRID, which studies galaxy formation, the merger of supermassive black holes, and reionization periods early in the history of the universe. universe. PRIYA goes one step further. It takes the galaxy information and black hole formation rules discovered in ASTRID and changes the initial conditions.

“With these rules, we can take the model we developed that matches the galaxy and the black hole, and then we vary the initial conditions and compare it to the Lyman Forest data from the neutral hydrogen eBOSS,” Byrd said.

‘Lyman-? ? ? The “forest” comes from a “forest” of tightly packed absorption lines in the quasar spectrum. These absorption lines are generated by electronic transitions between the energy levels of neutral hydrogen atoms. “The Forest” shows the distribution, density and temperature of giant intergalactic neutral hydrogen clouds. What’s more, the clumps of gas show the presence of dark matter, a hypothetical substance that has yet to be seen and is evident through observations of its tug on galaxies.

PRIYA simulations have been used to refine the cosmological parameters in the work submitted to JCAP September 2023 by Simeon Bird and colleagues MA Fernandez and Ming-Feng Ho at the University of California, Riverside.

Previous analyzes of neutrino mass parameters were inconsistent with data from the cosmic microwave background (CMB), which is described as the afterglow of the Big Bang. Astronomers used the Cosmic Microwave Background data from the Planck Space Observatory to place strict limits on the mass of neutrinos.

Neutrinos are the most abundant particles in the universe, so accurately determining their mass values ​​is important for cosmological models of the large-scale structure of the universe.

“We performed a new analysis through simulations, which were larger and better designed than before. The earlier differences with the Planck CMB data disappeared and were replaced by another tension, similar to that found in other low-redshift That’s what you see in large structural surveys,” Bird said. “The main result of this study is confirmation that the 8 tension between CMB measurements and weak lensing exists at redshift 20 billion years ago.”

“One of the tightly constrained parameters in the PRIYA study is 8, which is the number of neutral hydrogen structures within 8 megaparsecs (2.6 million light-years). This indicates the number of dark matter clumps floating around out there,” Byrd said. .

Another constrained parameter is ns, the scalar spectral index. It has to do with how the unwieldyness of dark matter changes with the size of the analyzed area. It shows how fast the universe expanded shortly after the Big Bang.

“The scalar spectral index determines how the universe behaved in the beginning. The whole idea of ​​PRIYA is to calculate the initial conditions of the universe and how the high-energy physics of the universe behaved,” Byrd said.

PRIYA simulations require supercomputers because they are so large, Bird explained.

“The memory requirements of the PRIYA simulations are so large that you can’t put them on any computer other than a supercomputer,” Byrd said.

The PRIYA simulation on Frontera is one of the largest cosmological simulations to date, requiring more than 100,000 core hours to simulate 3072 systems³ (about 29 billion) particles are located in a “box” with an edge of 120 megaparsecs (about 3.91 million light-years in diameter). PRIYA simulations consumed over 600,000 node hours on Frontera.

“Frontera is very important to this research because the supercomputer needs to be big enough so that we can run one of these simulations fairly easily, and we need to run a lot of simulations. Without something like Frontera, we wouldn’t be able to solve them.” It’s not that it takes a long time, it’s that they can’t run at all,” Bird said.

In addition, TACC’s Ranch system provides long-term storage of PRIYA simulation data.

“The ranch is important because now we can repurpose PRIYA for other projects. This could potentially double or triple our scientific impact,” Byrd said.

“Our thirst for more computing power is insatiable,” Bird concluded. “It’s crazy that we’re sitting on this little planet looking at so much of the universe.”