Effect of magnetization at late times on PPI-saturated self-gravitating accretion disks: simulations in full GR*

We present the results of our dynamical-spacetime magnetohydrodynamic study on the effects of magnetic fields on self-gravitating accretion disks around spinning black holes (a/M = 0.7). When no magnetic fields are present, these systems are unstable to the Papaloizou-Pringle Instability (PPI) which saturates and produces strong gravitational waves (GW), detectable to cosmological distances by third-generation GW observatories. Prior studies in fixed spacetime have shown that small seed fields can initiate rapid growth of the magneto-rotational instability (MRI) in disks without self-gravity, which strongly suppresses the PPI and prevents GW emission. Here we instead wait for the self-gravitating disks to reach a PPI-saturated state, then insert small seed magnetic fields to test how they could effect the dynamics of highly asymmetric massive disks. For spinning and non-spinning black holes, we find the MRI reduces the amplitude of PPI modes and their associated GWs. Magnetic fields reduce the maximum detection distance by Cosmic Explorer from 300 Mpc to 45 Mpc for a 10 solar mass system, by LISA from 11500 Mpc to 2700 Mpc for a 2 × 10⁵ solar mass system, and by DECIGO from z ≈ 5 down to z ≈ 2 for a 1000 solar mass system.