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John Bahcall Lecture Series

Measuring the Hubble Constant using Gravitational Lenses

Presented by: Roger Blandford (Kavli Institute for Particle Astrophysics & Cosmology, Stanford University)
Category: Science Colloquia   Duration: 1 hour   Broadcast date: February 22, 2011
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As first pointed out by Refsdal, multiple images of a variable source created by a gravitational lens can provide a measurement of the Hubble constant. This method has been applied to many gravitational lenses with outcomes that have been as varied as those resulting from traditional approaches. However, recent studies have been more thorough and resulted in more accurate and credible measurements. The successes and remaining challenges of this approach will be summarized paying particular attention to the analysis of fifteen years of observation of B1608+656, which yielded a result H_o= 71+/-3 km s-1 Mpc-1, making some strong assumptions about the underlying cosmology and the modeling. Currently the accuracy of this measurement appears to be limited by the effects of inhomogeneity along the line of sight on ray propagation. A new formalism and observational program for handling this will be described.

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Roger Blandford JPEG image (.jpg)
Roger Blandford's presentation PowerPoint (.ppt)