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Supermassive Black Holes in Nearby Galaxies: New Insights on Accretion Disk Physics

Speaker Dr. Luis C. HO
Affiliation Staff Astronomer, Carnegie Observatories, USA
Date December 11, 2009 (Fri)
Time 4:00-5:00 p.m.
Venue Room 522, 5/F, Chong Yuet Ming Physics Building, HKU

Abstract:

A significant fraction of nearby galaxies show evidence of weak nuclear activity unrelated to normal stellar processes. Recent high-resolution, multiwavelength observations indicate that the bulk of this activity derives from black hole accretion with a wide range of accretion rates. The low accretion rates that typify most low-luminosity active galactic nuclei induce significant modifications to their central engine. The broad-line region and obscuring torus disappear in some of the faintest sources, and the optically thick accretion disk transforms into a three-component structure consisting of an inner radiatively inefficient accretion flow, a truncated outer thin disk, and a jet or outflow. The local census of nuclear activity supports the notion that most, perhaps all, bulges host a central supermassive black hole, although the existence of active nuclei in at least some late-type galaxies suggests that a classical bulge is not a prerequisite to seed a nuclear black hole.

 

Coffee and tea will be served 20 minutes prior to the seminar.