Inner Accretion Disk Structure & Evolution
Can we see signatures of the spacetime around a black hole by looking at the light the inner accretion disk emits? Interpreting that light requires understanding where the emitting plasma ends—and whether that boundary actually traces the innermost stable circular orbit (ISCO), as standard spectral models often assume.
What I’ve shown
Using global simulations that evolve proton and electron fluids separately, I showed that a decreasing gas supply weakens collisional energy exchange between protons and electrons, causing a transition at radii larger than the ISCO. Electrons radiate efficiently, but cooling the protons requires transferring their energy to electrons through collisions. When this exchange becomes too slow, the protons retain their heat, changing the disk’s structure and producing a hot, X-ray-emitting atmosphere known as a corona.
This result connects a microscopic interaction to the large-scale geometry assumed when interpreting black hole emission.
This video shows the transition from a hot accretion flow to a cold disk when the accretion rate increases, demonstrating how Coulomb collisions collapse the two-temperature flow into a single-temperature disk.My earlier work also predicts emission from inside the innermost stable circular orbit that changes with spin, challenging the assumption in standard spectral models that the emitting disk ends at this boundary. Together, these results show why the emitting region’s relationship to the ISCO must be understood before using its radiation to infer black hole spin.
Read more in my research note on emission from the plunging region →
What I’m investigating next
How does electron-proton energy exchange shape the emergence of an X-ray corona, and how does the evolving disk affect measurements of black hole spin? With a student, I am developing an analytic model that connects electron-proton decoupling to the declining supply of stellar debris in tidal disruption events. This will test whether collisional energy exchange explains the delayed onset of X-rays.
I am also investigating how the evolving inner disk changes the emitting region used in spectral measurements of black hole spin.