Astrophysicists Simulate Evolution of Primordial Gas to Black Hole Feeding Disks

They challenged long-held astronomical theoriesو setting the stage for new insights into galaxy and black hole evolution.

Using a pioneering computer simulation, researchers have for the first time accurately simulated the journey of primordial gas from its origins in the early universe to its transformation into a swirling disk that fuels a single supermassive black hole. This achievement, detailed in The Open Journal of Astrophysics, marks a significant departure from established beliefs dating back to the 1970s and promises profound implications for our understanding of how galaxies and black holes evolve.

"Our new simulation represents the culmination of years of collaborative effort between two major initiatives here at Caltech," explained Phil Hopkins, the Ira S. Bowen Professor of Theoretical Astrophysics. The first initiative, FIRE (Feedback in Realistic Environments), focused on broader cosmological scales, addressing questions about galaxy formation and the impact of galaxy collisions.

In contrast, the STARFORGE initiative examined smaller scales, such as the formation of stars within individual gas clouds.

"There existed a substantial gap between these two scales," Hopkins noted. "Now, for the first time, we've successfully bridged that divide."

To achieve this breakthrough, the team developed a simulation with a resolution more than 1,000 times higher than previous efforts in the field. Surprisingly, their findings revealed that magnetic fields play a significantly larger role than previously thought in shaping and sustaining the vast disks of material surrounding and feeding supermassive black holes.

"Our previous theories suggested these disks should resemble flat crepes," Hopkins remarked. "However, observational evidence showed they're more akin to fluffy angel cakes. Our simulation clarified that magnetic fields are crucial in supporting and shaping these disks, contributing to their fluffy nature."

The simulation also involved a detailed "super zoom-in" on a supermassive black hole, illuminating the mechanisms by which gas and dust, drawn by immense gravitational forces, form accretion disks rather than immediately falling into the black hole. These disks, which radiate substantial energy, remain central to understanding quasars—highly active supermassive black holes—at the heart of distant galaxies.

While previous imaging efforts, including those by the Event Horizon Telescope, captured accretion disks around black holes in the Milky Way and Messier 87, these disks differ significantly from those found around quasars due to their proximity and relative calm.

To visualize the complex dynamics around active black holes, astrophysicists employed supercomputer simulations, integrating physics from gravity to dark matter dynamics across thousands of processors. This computational approach enabled them to model intricate phenomena, including stellar feedback—where stars influence their environments through radiation, stellar winds, and supernova explosions.

The challenge lay in developing a simulation that could span cosmic scales, integrating both galactic and accretion disk physics. The team utilized the GIZMO code, adaptable for both large-scale cosmological studies and detailed accretion disk simulations, facilitating a comprehensive understanding of black hole feeding mechanisms.

"In our simulation, we observed the formation of an accretion disk around a black hole," Hopkins described. "What surprised us was that this simulated disk defied longstanding assumptions about its structure."

Contrary to 1970s theories emphasizing thermal pressure in disk stability, the simulation highlighted magnetic fields' dominance, exerting pressures thousands of times greater than thermal forces.

"These magnetic fields serve multiple roles, including supporting the disk structure and enhancing its 'fluffiness'," Hopkins explained. This discovery reshapes predictions about disk characteristics, including mass, density, and material movement dynamics, influencing broader studies on galaxy mergers, star formation, and early universe star evolution.

As Hopkins looks to future research directions, he anticipates exploring detailed phenomena such as galactic mergers, unique star formation environments, and the nature of early universe stars.

"There's so much potential for discovery," he concluded.