A team of astrophysicists led by Caltech has managed for the first time to simulate the journey of primordial gas dating from the early universe to the stage at which it becomes swept up in a disk of material fueling a single supermassive black hole. The new computer simulation upends ideas about such disks that astronomers have held since the 1970s and paves the way for new discoveries about how black holes and galaxies grow and evolve.

"Our new simulation marks the culmination of several years of work from two large collaborations started here at Caltech," says Phil Hopkins, the Ira S. Bowen Professor of Theoretical Astrophysics.

The first collaboration, nicknamed FIRE (Feedback in Realistic Environments), has focused on the larger scales in the universe, studying questions such as how galaxies form and what happens when galaxies collide. The other, dubbed STARFORGE, was designed to examine much smaller scales, including how stars form in individual clouds of gas. "But there was this big gap between the two," Hopkins explains. "Now, for the first time, we have bridged that gap." To do that, the researchers had to build a simulation with a resolution that is more than 1,000 times greater than the previous best in the field.

To the team‘s surprise, as reported in The Open Journal of Astrophysics, the simulation revealed that magnetic fields play a much larger role than previously believed in forming and shaping the huge disks of material that swirl around and feed the supermassive black holes. "Our theories told us the disks should be flat like crepes," Hopkins says. "But we knew this wasn‘t right because astronomical observations reveal that the disks are actually fluffy—more like an angel cake. Our simulation helped us understand that magnetic fields are propping up the disk material, making it fluffier."