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CfA theory seminars

CfA theory seminars this week:

Tue, Dec 9, 12:30pm

Aristotle Socrates (UCSB)

Stability, Turbulence, and Gravitational Energy Release
in Black Hole Accretion disks

Fluid dynamical and spectral modeling of accretion onto a black hole has
advanced significantly over the last few decades.  However, progress
towards understanding the mechanics of the flow and the spectrum which it
radiates has occurred separately, with little quantitative connection
between the two.  Under the framework of radiation magnetohydrodynamics, I
will show that magnetized accretion disks are dynamically unstable to
photon bubble-like instabilities.  I will discuss how these
radiation-driven fluid instabilities alter the disk's vertical structure
and emergent spectrum.  Also, I will consider how the turbulence, which is
required for angular momentum transport, affects the thermal spectrum of
the putative disk.  Since the turbulent velocities of the accretion flow
may exceed the electron thermal velocity, bulk Comptonization by the
turbulent motions themselves, in other words turbulent Comptonization, may
serve as the radiation mechanism which mediates gravitational energy
release.  Turbulent Comptonization provides an intrinsic source of X-ray
photons while giving observers the ability to constrain properties of the
turbulence itself.

The seminar will be held in Pratt Conference Room (G04) at CfA.


Wed, Dec 10, 2pm

Savvas Koushiappas (Ohio State University)

Forming Supermassive Black Hole Seeds from Low-Spin Material

I will present a model in which the seeds of supermassive black holes
are formed from the low angular momentum material in proto-galaxies.
These seed black holes have a universal mass of ~10^5 Msun.
I will show that under reasonable assumptions this model predicts a
linear relationship between the masses of the supermassive black hole
and its host spheroid.

The seminar will be held in Pratt Conference Room (G04) at CfA.


Fri, Dec 12, 11am

Recent Work on Weak Gravitational Lensing AND Close Pairs of Quasars
in the Sloan Digital Sky Survey

Joseph Hennawi (Princeton)

I will present on two topics. The first talk will be on weak
gravitational lensing. The second talk will be on close pairs of quasars in
the Sloan Digital Sky Survey (SDSS). The number of close < 60" quasar pairs
is over two orders of magnitude larger than expected from extrapolations of
the quasar correlation function to small scales. We have already nearly
doubled the number of known close quasar pairs, and preliminary results 
be highlighted. I will discuss observational strategies for finding close 
and the manifold science motivations, including quasar clustering, the
search for strong gravitational lensing by clusters of galaxies, and using
close pairs of quasars to study the Lyman alpha forest and the IGM.

The seminar will be held in Phillips Auditorium at CfA.