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Blue Waters and XSEDE user Charles Gammie contributes to M87 black hole image

Thanks in part to the power of the Blue Waters supercomputer and the Extreme Science and Engineering Discovery Environment (XSEDE), both headquartered at NCSA and supported by the National Science Foundation, a massive research collaboration was able to capture a picture of a black hole for the first time ever.

A research team led by Charles Gammie, a professor of Physics and Astronomy at the University of Illinois at Urbana-Champaign and a user of both Blue Waters and XSEDE resources, played a vital role in laying the groundwork in the imaging of the M87 black hole. The image was captured by the Event Horizon Telescope (EHT) collaboration, a global network of radio dishes that use short radio wavelengths to construct the equivalent of a giant interferometer, which helps to track the size and movement of black holes.

Through simulations on XSEDE resources and the Blue Waters system at NCSA, Gammie and his team were able to take on massive simulations of astrophysical data. In order to lay part of the groundwork for this discovery, Gammie’s lab used Blue Waters’ unique power to investigate magnetized turbulence, one of the many mysteries shrouding black holes.

“We think that there’s hot gas circulating around the black hole and that the hot gas is turbulent. At Blue Waters, we studied that turbulence using a special numerical setup, and built the highest-resolution models of that kind of magnetized turbulence that had ever been done,” said Gammie.

“These simulations gave us more confidence in the simulations that we did to model M87. The turbulence in the gas that’s circulating around the black hole is fundamental to the entire process. We wanted to check whether we were getting that right, or whether we had to use 2x or 10x the resolution to get it done. Blue Waters enabled us to do that check.”

Next, Gammie’s team used an XSEDE allocation on the Stampede2 supercomputer, located at the Texas Advanced Computing Center (TACC), to perform even more simulations.

“On Stampede2 we ran large hydro simulations of the gas orbiting and falling into the black hole. We also ran synthetic imaging software, developed in our group, that takes the data from these large hydro simulations and makes a relativistically consistent image from it,” said Gammie. “We include the bending of light around the black hole and time delays and all of the strange things that happen around black holes.”

Through these simulations, Gammie and his team provided important analysis to the imaging process, building theoretical models for researchers to use as a guide for what a potential black hole image might look like, which helped inform their data-taking strategy.

“When we went to interpret the EHT data, we used these simulations to build a huge library of simulations and synthetic images based on the simulations. We then compared the images to the EHT results to see which models worked and which didn’t,” said Gammie. “We ran around 60 simulations and we have in excess of 60,000 synthetic images based on those simulations.”

“In particular, we found that the models in which the black hole is not spinning, do not work,” Gammie continued. “Only the black holes with spin were consistent with EHT data and other observations of M87.”

With the theoretical models and high-resolution simulation, Gammie and his team were able to provide clear a clear interpretation of the data for the EHT collaboration, ultimately contributing important information to the first-ever image of a black hole, an emphatic moment in human scientific history.

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