Determine the black-hole spin of M87* despite uncertain electron microphysics

Determine the spin of the M87* black hole by resolving the uncertainty in the electron temperature or electron distribution function arising from plasma microphysics not captured by global magnetically arrested disk simulations.

Background

The paper models horizon-scale emission from M87* using global three-dimensional general-relativistic magnetohydrodynamic simulations of magnetically arrested accretion disks. Although the simulations describe the bulk accretion-flow dynamics, they do not self-consistently determine how electrons are heated or how their energy distribution is shaped by processes such as plasma waves and kinetic instabilities.

Because the emitted synchrotron radiation depends sensitively on the electron temperature and on whether the electrons follow a thermal or non-thermal distribution, the uncertainty in electron microphysics propagates into the interpretation of EHT observations and prevents a definitive determination of the black-hole spin. The paper addresses this issue phenomenologically by exploring several electron-temperature prescriptions, thermal and non-thermal distributions, and multiple spin values, but it does not resolve the underlying microphysical uncertainty.