The Universe

Simulating Realistic Structures of Accretion Disks Around Supermassive Black Holes

Image from visualization showing density evolution of an accretion disk around a supermassive black hole
Visualization showing density evolution of an accretion disk around a supermassive black hole. The density isosurface (bottom left) corresponds with the colors, which show the value of radiation energy density as indicated by the color bar. The gas heats up when it flows towards the black hole, photons are emitted from the disk surface, and magnetic fields are amplified. Toward the end of the video, most of the gas has accreted and the remaining gas flows towards the black hole along the filamentary magnetic fields instead of around the disk. Yan-Fei Jiang, Flatiron Institute; Patrick Moran, NASA/Ames

When gas flows towards a black hole, it heats up by converting gravitational potential energy into thermal energy and emits photons in wavelengths ranging from optical to ultraviolet (UV) and X-rays. This forms accretion disks, which are believed to be the fundamental process that produces the observed active galactic nuclei (AGNs)—luminous phenomena that contain supermassive black holes at the center of many galaxies. In this project, scientists from the Flatiron Institute’s Center for Computational Astrophysics performed a series of three-dimensional radiation magnetohydrodynamic simulations to study how the accretion process works for a wide range of accretion rates. They were able to demonstrate the important role of magnetic fields, not only for transporting angular momentum, but also for supporting the vertical structure of the accretion disk. These simulations revealed how UV/optical photons are generated and may explain various phenomena seen when AGN observations were compared with the traditional disk models.

Quick Facts

High-performance computers are crucial for studying the properties of black hole accretion flows with the goal of understanding the observational properties of AGNs. NASA’s supercomputers are uniquely able to provide us with more than 30 million processor-hours continuously so that we can explore different parameters and understand the results systematically.

Yan-Fei Jiang,
Flatiron Institute
  • The team simulated the UV/optical emission regions of accretion disks around supermassive black holes over a wide range of accretion rates with self-consistent radiation magnetohydrodynamics in 3D, and then studied how magnetic fields changed the accretion disk structures compared with the standard model for active galactic nuclei.
  • Each simulation was run on 30-50 AMD Rome nodes for several weeks on the Aitken system at the NASA Advanced Supercomputing facility.
  • The results demonstrate, for the first time, that accretion disks around AGNs likely have a thin accretion layer near the disk midplane and a much more extended optically thick layer on top of the disk due to rotationally amplified magnetic fields. These results can help build the next generation of accretion disk models for AGNs.
  • Based on these simulations, the team will calculate broadband spectra and compare them with observed spectra of AGNs—a critical step for verifying the simulation results.

Researcher

  • Yan-Fei Jiang, Flatiron Institute

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