Akshay
Singh
Bar-Ilan University
Accretion disks play a central role in shaping the dynamics around black holes. The magnetically arrested disk (MAD) state, in which magnetic flux near the event horizon saturates, has gained prominence following Event Horizon Telescope observations of M87* and Sagittarius A*, suggesting that many supermassive black holes may operate in this regime. Low-luminosity systems such as Sgr A*, however, are strongly affected by radiative cooling, which can modify the thermal, magnetic, and dynamical structure of the disk.In this talk, I examine how radiative cooling influences MADs at sub-Eddington accretion rates. Analytically, we identify a critical accretion rate above which synchrotron emission becomes the dominant cooling mechanism, shifting the thermal equilibrium and altering the MAD parameter. Using GRMHD simulations with our GPU-accelerated code cuHARM, I show how these cooling effects modify magnetic saturation, flux eruptions, force balance, and jet efficiency across a range of black hole spins and accretion rates. I also discuss how the traditional measure of disk height can be misleading in MAD systems, motivating the need for a revised definition. These results clarify how cooling regulates MAD dynamics in low-luminosity black holes and may help interpret future EHT observations.
Location: room 203, also available via Zoom
Zoom details:
https://us06web.zoom.us/j/81514948789?pwd=k4HQdJZ8bJzi4cFwlJUDIGytri1JIW.1
Meeting ID: 815 1494 8789
Passcode: 799936
