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CfA theory seminar

Joint Cosmology Seminar of Harvard/MIT/Tufts

Tue, Feb 10, 2:30pm

Vicky Kalogera (Northwestern University)

The Most Relativistic Double Pulsar: Implications for Gravitational-Wave
Detection and Neutron-Star Formation

The recent discovery of the first double pulsar system PSR J0737-3039
promises to be best laboratory ever found for general relativity and
pulsar physics. I will discuss our current expectations for
gravitational-wave detection and our current understanding of
neutron-star formation in view of this exciting discovery.

The seminar will be held in the Gilman room in Agassiz house, Radcliffe
Institute (at the corner of Mason and Garden St. 10 min walk from CfA) at


Special Theory Seminar

Wed, Feb 11, 12:30pm

Stuart Wyithe (Univ. of Melbourne)

The Highest Redshift Quasars and the Reionization of Cosmic Hydrogen

In recent years we have seen the first observations of the epoch of
reionization. Quasars have been discovered by the SDSS at redshifts as
high as z~6.4. Their spectra reveal a universe that is opaque to
Ly-alpha photons implying that intergalactic hydrogen was still partially
neutral at that time. In addition, the spectra also show giant regions of
ionized gas surrounding the quasars. I will describe how the extent of
these ionized regions implies a neutral fraction of intergalactic hydrogen
that is near unity at z~6.3. While quasar absorption studies suggest that
reionization occured near z~6, the WMAP experiment has found a high
optical depth to Thomson scattering of CMB photons by free electrons along
the line of sight. This implies significant reionization of cosmic
hydrogen at redshifts as high as z~20, much earlier than the z~6 implied
by the SDSS quasars. I will discuss how an early generation of massive
population-III stars could provide a resolution to this dissagreement.
Finally I will describe some of the possibilities for redshifted 21cm
observations near high redshift quasars with planned instruments like

The seminar will be held in Pratt Conference Room (G04) at 12:30pm.