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GCS supercomputers help create first image of

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In April 2019, the Event Horizon Telescope (EHT) collaboration unveiled the first-ever image confirming the existence of a black hole. The image shows the black hole at the center of the distant galaxy Messier 87 (M87), located more than 50 million light-years from Earth.

To the outside observer, the reveal of the first image of the M87 was the culmination of a multi-year effort that pooled resources, facilities, expertise and tools from around the world. The EHT was far from over, however, and in May 2022 it unveiled a new image of a black hole, this time at the center of our own galaxy, the Milky Way.

Astronomers have been hypothesizing the existence of a black hole in the middle of the Milky Way since Karl Jansky in 1933 named the mysterious radio signal from the center of our galaxy Sagittarius A* (Sgr A*). Until now, however, researchers could not confirm its existence. By bringing together observers from the world’s leading astronomical observing facilities with theorists who use high-performance computing (HPC) to develop models of black hole accretion and emission, the EHT has provided definitive proof that the Jansky’s hypothesis is true.

Among the contributors to the EHT consortium is Professor Dr. Luciano Rezzolla from Goethe University Frankfurt, whose team used HPC resources from the High-Performance Computing Center Stuttgart (HLRS) and the Leibniz Supercomputing Center (LRZ) to create high resolution models. of the black hole. HLRS and LRZ are member centers of the Gauss Center for Supercomputing (GCS).

“Our team performs simulations by solving the equations of general relativistic magnetohydrodynamics (MHD) and radiative transfer,” explained Rezzolla. “That way we can produce images that are mathematically and physically consistent, which can then be compared with images coming from observations,” Rezzolla said. “For M87, we made about 60,000 images of simulation, but for Sgr A*, we produced nearly two million of them.”

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Calculation at the center of the galaxy

Although it seems counterintuitive, EHT researchers had to create many more simulation images of Sgr A* due to its relative proximity to Earth. “Sgr A* is an object that we know very well from an astronomical perspective,” Rezzolla said. “There are decades of observations made at many different wavelengths, which put constraints on our theoretical models, and we had to do a lot more investigation to convince ourselves that what we were seeing was a hole. From a computational perspective, that means using a lot more simulations than we did to model M87, and not just in terms of resolution and physical condition, but in terms of microphysical modeling, which had to be revised and extended.

Working on the M87 galaxy, the researchers learned that making their codes as generic as possible would not only ensure that they accounted for many complex, possibly unknown, physical phenomena surrounding a black hole, but also that they could apply their methods to other celestial objects like Sgr A*. The team is also working in parallel with a group from the University of Illinois at Urbana-Champaign and the National Center for Supercomputing Applications (NCSA) and has put considerable effort into verifying that the respective computer codes of the two teams are designed to produce the same results. when given the same inputs.

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Essentially, the two teams follow a similar approach: First, they run detailed MHD simulations, which produce models of the dynamics of the astrophysical plasma as gravity pulls it into the black hole. Once the simulation data is available, researchers then focus on developing images that not only accurately reflect the data from the simulations, but also what would be observed from a terrestrial observatory. These images are then compiled to create a rendering of the black hole’s “shadow” or pattern of light and plasma flowing around the edges of the black hole. Because black holes don’t emit light, this shadow is the only way to really reveal their presence.

GCS System Upgrades Strengthen Data-Intensive Applications

While the Sgr A* black hole was more difficult to model than the M87 black hole, Rezzolla pointed to advances in computing, including next-generation systems both HLRS and LRZ, that helped the team overcome these hurdles. more and to create its models more efficiently than during the M87 works. “We had better code and better models for this work, as well as access to better computers through GCS. This meant we could run many more models than we could manage in the past, and the time to execution was shorter in some cases. This reduced our analysis time,” he said. “We published our findings on the M87 in 2019, which means that most of the work has been done in 2018, and the same timeframe is true here, so you’re looking at a 4 year gap in the machines and can see a big jump in performance.”

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After reaching this milestone, the team from Goethe University Frankfurt began to focus their research efforts on thoroughly examining the polarity of light in their simulations. Astronomers have at least two different theories about the role magnetic fields play when plasma accretes onto a black hole. By studying how light moves and bends in this space, Rezzolla and his team aim to improve our understanding of a phenomenon we are only beginning to understand.

Rezzolla said that going forward, the team wants to work more closely with user support staff at GCS Centers to help optimize its compute code, especially to take advantage of GPU accelerators, which have become a increasingly important computing technology that can help researchers working on more data-intensive applications.

Funding for Hawk was provided by the Baden-Württemberg Ministry of Science, Research and the Arts and the German Federal Ministry of Education and Research through the Gauss Center for Supercomputing (GCS).

Funding for SuperMUC-NG was provided by the Bavarian Ministry of Science and Arts and the German Federal Ministry of Education and Research through the Gauss Center for Supercomputing (GCS).

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