Ground and space based observations spanning the radio to gamma-ray frequency range show that stellar mass black holes part of black hole X-Ray binaries (BHXRBs) cycle through different spectral states of accretion over the course of months to years. BHXRBs spend most of their time in the quiescent state, characterized by a low luminosity and geometrically thick accretion disk. In many systems this is followed by brief outbursts where the luminosity comes close to the Eddington limit and radiative cooling causes the disk to become geometrically thin. These spectral state transitions harbor unique information about fundamental accretion disks physics, but simulating them proved to be extremely challenging.

Here you see the first GRMHD simulation of a black hole spectral state transition that includes radiation and evolves the ion and electron temperatures separately. I rescale the density high to low such that the accretion rate corresponds to a certain (decreasing) fraction of the Eddington mass accretion rate, and, calculate the corresponding luminosity in Eddington units. At low accretion rates, the optical depth decreases and the radiation leaks out, causing the disk to become thinner.

We expect to publish these results in the 2023 timeframe.

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