Omer Bromberg (Tel Aviv University)
Black-holes are like the genie of the lamp, as they can store vast amounts of energy within an extremely compact region. Under the right conditions, this energy can be harnessed to power some of the most luminous and energetic phenomena in the universe, like quasars and gamma-ray bursts. Current theoretical understanding suggests that the energy release is facilitated by the black-hole’s rotation and its interaction with magnetic fields supplied by accreted matter. Yet, how the black-hole magnetosphere responds to the energy extraction and by what processes this energy is ultimately converted into the observable emission is still debated. In this talk, I will discuss the necessary conditions near the event horizon that can sustain a stable energy extraction. I will trace the path of the outflowing energy that gives rise to relativistic jets and examine the mechanisms responsible for converting the energy into the observed light. These processes may offer insights into recent observations of core emission from black hole-powered systems.
Abbas Askar (CAMK, Warsaw)
Black holes with masses ranging from a few hundred to hundreds of thousands of solar masses, known as intermediate-mass black holes (IMBHs), remain elusive, and their formation pathways are still not fully understood. Dense star clusters have long been proposed as promising environments for both the formation and subsequent growth of IMBHs. In this talk, I will discuss the dynamical formation channels of IMBHs based on results from detailed Monte Carlo and direct N-body simulations of star clusters. I will describe how runaway stellar collisions, followed by tidal disruptions, can lead to the early formation and gradual growth of IMBHs, and how these processes depend sensitively on the initial properties of the host cluster. I will also discuss the observational implications of these growth channels, particularly for gravitational wave sources and electromagnetic transients. The long-term evolution of IMBHs within massive clusters will also be addressed, including their potential migration toward galactic centers and their role as seeds for the eventual formation of supermassive black holes.
Swadesh Chand (to be confirmed) (Inter-University Centre for Astronomy and Astrophysics, India)
Maciek Wielgus (Instituto de Astrofisica de Andalucia, Granada, Spain)
Very long baseline interferometry (VLBI) offers a way to study AGN jets with an exceptionally high angular resolution, zooming into the zone of the jet collimation and acceleration. In particular, a global array of the Event Horizon Telescope (EHT) offers unprecedented resolution with highest VLBI observing frequency of 230 GHz. During the first observing campaign of the EHT in 2017, observations of 16 AGN sources were carried out. Together with the previous measurements at lower radio frequencies, these new observations allow for a statistical study of the properties of AGN cores across the angular scales. We observe a persistent and statistically significant effect of brightness temperature increase with the distance from the central black hole, which indicates evolution of Doppler factors in accelerating jets and a gradual conversion of the magnetic energy into kinetic energy. I will describe these observations and discuss what they teach us about the AGN jets.
