Indonesian Students Club

Indonesian Students Club

skip to events

calendar tabs

  •  All 
  • Grid
  • Month
  • Week
  • Day
  • (Selected tab) Detail

Event Detail Information

Event Detail Information

Astronomy Colloquium: "Stars Wake up the Giants: Flares and Transient Jets from Quiescent Galactic Centers"

Speaker Dimitrios Giannios, Assistant Professor, Purdue University
Date Dec 3, 2013
Time 4:00 pm - 5:00 pm  
Location Astronomy 134
Sponsor Department of Astronomy
Event type Colloquia
Views 9208
The majority of the supemassive black holes in galactic centers, including that in our own Galaxy, are dormant. Our knowledge of the properties of quiescent accretion and the environments of quiescent galactic centers is very limited. In this talk, I will discuss 2 examples in which stars can be used as unique probes of quiescent galactic centers. The tidal disruption of a star by a supermassive black hole provides us with a rare glimpse of these otherwise dormant beasts. It has long been predicted that the disruption will be accompanied by a thermal `flare', powered by the accretion of bound stellar debris. Recently, we explored the observational consequences if a fraction of the accretion power is channeled into an ultra-relativistic outflow. The high-energy transient Sw 1644+57 provides strong support to the presence of powerful relativistic jets during tidal disruption events. I will discuss the rich behavior of Sw 1644+57 in the radio and X-rays, focusing on the information we gain on the circum-nuclear medium and the jet physics by modeling this event. Our Galactic center contains a cluster of stars in the inner 0.1 pc. This, so called, S cluster is thought to coexist with the quiescent accretion disk. Because of its early stellar type, the S2 star of the cluster is expected to posses a fairly powerful wind. We show here that the ram pressure of the accretion disk shocks the stellar wind fairly close to the star. The shocked fluid reaches a temperature of ˜1 keV and cools efficiently through optically thin, thermal bremsstrahlung emission. The radiation from the shocked wind peaks around the epoch of the pericentre passage of the star at a luminosity potentially comparable to the quiescent emission detected from Sgr A*. Detection of shocked wind radiation can constrain the density of the accretion disc at a distance of several thousands of gravitational radii from the black hole.
link for robots only