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Rapid Black Hole Spin-down by Thick Magnetically Arrested Disks

  • Authors: Beverly Lowell, Jonatan Jacquemin-Ide, Alexander Tchekhovskoy, Alex Duncan

Beverly Lowell et al 2024 The Astrophysical Journal 960 .

  • Provider: AAS Journals

Caption: Figure 5.

Dimensionless spin-up parameter s as a function of BH spin a for the MAD and NT disk models. We show the NT model in blue. The MAD hydrodynamic disk is shown in orange, and our model for the disk is shown by the dashed orange line. In an MAD, the disk component follows a similar trend as the NT disk, but its torque on the BH is much smaller except at the highest spin values. The EM component is shown in green, with our jet model shown by the green dashed line. The total MAD data is shown by red points, and our total MAD spin-down model is shown by the thick, red curve. The values of equilibrium spin a eq for the MAD and NT disks are shown as vertical lines at a = 0.1 and a = 1, respectively: these are where the spin-up curves vanish, s = 0. We note that the thickness of the vertical lines does not correspond to uncertainty. Our semi-analytic s MAD model agrees well with the simulation data. Differences for positive spin are primarily caused by an imperfect fit for η EM (as can be seen in Figure 3), affecting s EM. Our semi-analytic model for MAD torques on the BH shows how and why MADs spin down their BHs to a very low value of a eq,MAD ≈ 0.07. MADs are significantly modified by the large-scale, dynamically important magnetic fields. Black triangles represent higher-resolution simulations with Γ = 13/9, demonstrating that higher Γ leads to stronger spin-down.

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