Simulations reveal surprising electron temperatures near M87 black hole’s event horizon

The first black hole images stunned the world in 2019, with headlines announcing evidence of a glowing doughnut-shaped object from the center of galaxy Messier 87 (M87 —55 million light years from Earth. Supercomputer simulations are now helping scientists sharpen their understanding about the environment beyond a black hole’s ‘shadow,’ material just outside its event horizon.

“Ever since we made that first black hole image, there’s been a lot of work trying to understand the environment just around the black hole,” said Andrew Chael, an associate research scholar at Princeton University and a fellow of the Princeton Gravity Initiative.

Chael is part of the Event Horizon Telescope Collaboration (EHT), which connects telescopes from around the world to form a mega-telescope roughly the size of Earth. The EHT uses a technique called Very Long Baseline Interferometry, a type of astronomical interferometry used in radio astronomy that compares telescope signals to stitch together images that resolve the M87 black hole.

Shown in the black hole image is light from hot electrons that spiral around surrounding magnetic field lines and produce synchrotron radiation.

“We want to understand the nature of the particles of this plasma that the black hole is eating, and the details of the magnetic fields commingled with the plasma that in M87 launches huge, luminous jets of subatomic particles,” Chael said.

Like a beacon, the jets signal the possible presence of a black hole in center of the M87 galaxy as it spews particles thousands of light years from the source.

Using supercomputers to simulate black hole plasma, magnetism, and gravity

Across the globe, scientists are harnessing the power of supercomputers to unravel one of the universe’s most extreme environments: the space around black holes.

Chael’s research group is among those using advanced simulations to model the dynamic interplay between high-energy plasma, powerful magnetic fields, and the overwhelming pull of gravity near these cosmic giants. These forces do not act in isolation—they interact in complex, feedback-driven ways that allow black holes to consume surrounding matter, launch jets across vast distances, and emit the glowing radiation captured by the Event Horizon Telescope.

Chael’s recent advancements in his simulation techniques are reported in his study published February 2025 in the Monthly Notices of the Royal Astronomical Society. They go beyond typical simulations that treat the electrically charged particles of protons and electrons in the plasma surrounding the black hole like a single fluid.

“This paper is a first attempt of using a more advanced, more computationally expensive technique to directly model these separate particle species of electrons and protons to try to understand how they interact, and in particular, what the relative temperature of the two is,” he explained.

The relative temperature between the electrons and protons determines the brightness and other properties of the black hole image.

“What we found through simulations is the temperature of the electrons is much higher than is typically thought to be the case in M87. We’re not able to reproduce the low polarization, which is one of the main constraints in understanding what the temperature of the plasma is around the black hole,” Chael said.

The results highlight a fundamental tension between current models of electron heating in plasma physics and the observational constraints provided by the EHT.

“It seems like the black hole in M87 has electrons that are about 100 times cooler than the protons. This is an interesting direction to proceed,” Chael said.

Chael completed his black hole simulations on the Stampede2 and later the Stampede3 supercomputers at the Texas Advanced Computing Center (TACC), with allocations awarded by the National Science Foundation(NSF)-funded Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program.

“I’ve been using XSEDE, and now ACCESS resources at TACC since graduate school,” said Chael. “It’s been the primary academic supercomputing center that I’ve run simulations for my research. These systems were both extremely easy to use with my code,” Chael said.

A series of 11 general relativistic magnetohydrodynamic simulations (GRMHDS) that cover a range of different black hole spins were completed on Stampede2 and Stampede3 for this study. Breaking that down, ‘general relativistic’ accounts for the strong gravity of the black hole spacetime. ‘Magnetohydrodynamic’ takes a fluid dynamics approach to the magnetic fields of the black hole.

More research ahead

There are several years of EHT data that hasn’t yet been imaged, and it hopes to make a movie that tracks its evolution over time.

In January 2025, Chael and his EHT collaborators published a study comparing the M87 black hole image captured by the EHT to a wide range of simulations. To support this work, he received computing allocations from ACCESS on the Stampede2 and Jetstream supercomputers, and he conducted simulations on the NSF-funded Frontera system at TACC.

High-resolution simulations revealed that while the black hole’s shadow remains remarkably consistent in size and general structure from year to year, it is far from static. Also, the brightest spot on the ring shifts over time, driven by turbulent mixing and dynamic flows of plasma near the event horizon. As different regions of gas heat up or cool down due to these chaotic processes, the black hole’s appearance subtly but measurably evolves.

“Black holes are extremely complicated environments,” Chael said. “The best available tools we have are supercomputing simulations. It’s amazing that we’ve been able to build these computers and codes that allow us to create accurate models of what’s going on in such a strange and complicated relationship. Simulations give us confidence that we are accounting for all these effects, which are all interacting in complicated and sometimes unpredictable ways.”