As astronomers look out at the distant cosmos, it's only natural that they would also look inward, to the center of our own galaxy, the Milky Way.
The Event Horizon Telescope has shared the first image of Sagittarius A*, the supermassive black hole at the center of the Milky Way. The view past the clouds of gas and dust - created with the help of the Frontera supercomputer at The University of Texas at Austin - revealed a black hole that is hot, dense and quickly changing, with a ring of superheated gas around its dark center.
The results provide overwhelming evidence that the object at our galactic center is indeed a black hole and yields valuable insights into the dynamics of such giants, which are thought to reside at the center of most galaxies.
The team's results were published today in a special issue of The Astrophysical Journal Letters.
The image was made possible through an innovative, data-driven approach to astronomy that combines observations from eight radio telescopes around the world to form an Earth-scale interferometer, the Event Horizon Telescope, or EHT, specifically to probe black holes.
The research was supported by UT Austin's Frontera supercomputer, the most powerful supercomputer in academia. Operated by the Texas Advanced Computing Center, Frontera is the National Science Foundation's flagship system for open science. Since 2021, a Large-Scale Community Partnership allocation let EHT-affiliated scientists use nearly 80 million CPU hours on Frontera.
The team used Frontera to create the largest-ever simulation library of black holes. By comparing these realistic models with observations, researchers were able to probe the physics of these extreme objects more completely than with either method alone.
The community modeling effort was led by Chi-kwan "CK" Chan (University of Arizona), Charles Gammie (University of Illinois at Urbana-Champaign), and Christian Fromm (Würzburg University).
"The accreting flow around the galactic center black hole is complex," said Chan, an associate research professor in the Steward Observatory at the University of Arizona. "Advanced computing systems like Frontera allow us to use cutting-edge computational science methods to model these complex systems, study the boundaries between order and chaos, and understand what we are seeing with the Event Horizon Telescope."
Gammie, a professor of physics at the University of Illinois at Urbana-Champaign, and his team are among the main developers of the computer code that simulates black hole physics.
"We produced a multitude of simulations and compared them to the data. The upshot is that we have a set of models that explain almost all of the data," Gammie said. "It's a triumph of computational physics."
After simulating Sagittarius A*, the researchers used Frontera, the Open Science Grid, and CyVerse to render physically accurate images and predict how our galaxy's black hole might appear from the vantage point of Earth. Many of these images closely matched the observations from EHT, giving added confidence to the team's results.
Beyond confirming observations, these high-performance computing-powered models provide a deep understanding on how Sagittarius A* is shaped by its plasma environment.
"By comparing these high-performance computing models and images with the observations, researchers pinned down the plasma properties around Sagittarius A* and performed a new test of Einstein's General Theory of Relativity in the strong gravity regime," he said.
The success of the project is spawning further studies to explore several unanswered mysteries, such as how Sagittarius A* changes over time and how it spins. Future research will probe the small discrepancies between computer models and observations, notably the variability of Sagittarius A*, which will need more complete computational models to fully understand, Gammie said.
"This image is a testament to what we can accomplish when, as a global research community, we bring our brightest minds together to make the seemingly impossible, possible," said Sethuraman Panchanathan, director of the National Science Foundation. "NSF is proud to be an international partner that invests in this innovative research and the infrastructure that makes such fantastic discoveries possible."
