Our department hosted the IAU Symposium 378 - Black Hole Winds at all scales, March 12-16, 2023. 70 astrophysicists, both experts and students, convened to discuss the latest findings on winds from black hole sources. The attendees spent five full days at the Technion campus in Haifa. The exciting and popular topic brought together observers of many different wavebands, which made for a multitude of new data being presented and discussed. There was a good mix of low-energy and high-energy observations, including the most advanced ground facilities and space observatories. Theoretical aspects of black hole outflows were also a big part of the discussions. The Symposium was organized by astrophysicists from all over the world, with Ehud Behar of our department as chair of the SOC.
The symposium covered a range of topics related to outflows from black holes. There was a good balance between the physics of the winds, and their impact on their surroundings. Interesting discussions took place such as one regarding the connection, or lack thereof, between outflows from supermassive black holes at the centers of galaxies, and those from stellar black holes. The multi-wavelength aspects were highlighted in both. It was interesting to see that even for specific well-studied sources it is hard to connect the molecular outflow with that of the UV, and the ultrafast sub-relativistic X-ray signatures. A dedicated session on radio emission from these sources made things even more complicated. Many new observations were presented. For example, IR astronomers presented recent James Webb Space Telescope data indicating significant galactic feedback at redshifts above z=6, when the Universe was only one billion yrs old. A discussion commenced on how actually to measure feedback, the impact of outflows on the host galaxy?
On the theoretical ground, a variety of simulations for magnetic and thermally driven winds were presented, some of which attempted to put galactic and stellar black hole winds on an equal footing. Cases from extreme mass accretion rates to advection dominated flows were covered. Topics of radiative driving and radiative transfer in outflows were discussed, a few of which even proposed comparisons with observations. An often overlooked, yet interesting topic was the influence of intermediate black hole systems on their dwarf galaxy hosts.
All in all, it was most gratifying to see researchers from different observational backgrounds and theoretical approaches all participate in the lengthy discussion periods provided after each session. Perhaps as expected, many fundamental puzzles about these winds remain.