Wednesday Colloquium


"Energy dissipation in relativistic jets"

Krzysztof Nalewajko (Copernicus Astronomical Centre, Warsaw)

"The question of relevant energy dissipation processes is central to understanding the physics of relativistic jets in radio-loud active galaxies and gamma-ray bursts. The standard scenario involving internal shocks faces several difficulties. Alternative mechanisms include stationary reconfinement shocks, magnetic reconnection and current-driven plasma instabilities


"Observational evidence for AGN feedback at pc scale"

Feng Yuan (Shanghai Astronomical Observatory, Chinese Academy of Sciences)

In a hot accretion flow, the radiation from the innermost region of the flow propagates outward and heats the electrons at large radii via Compton scattering. When the radiation is strong enough, L > 0.02 L_Edd, the electrons will be heated to be above the virial temperature. In this case, the BH activity will oscillate. We show that this mechanism can explain the intermittent activity of some compact young radio sources.


"The First Supermassive Black Holes"

Mitch Begelman (JILA, Boulder, Colorado)

The supermassive black holes that populate galactic nuclei could have grown from an early population of stars, or via the direct collapse of much larger masses of gas. I will discuss recent investigations of the latter possibility, focusing on the physics that may have regulated early black hole formation and growth. Black hole formation by direct collapse implies the existence of hitherto undetected classes of objects; I will outline the prospects for detecting them.


"On the existence of stellar mass binary black holes"

Tomasz Bulik (OAUW, Warsaw)

I will describe the ups and downs of looking for binary black holes. I will discuss the constraints on their abundance and formation rate in the local Universe.