Research Interests

I am a Professor of Astronomy and Physics at the Johns Hopkins University and a Senior member of the Science Staff at the Space Telescope Science Institute, where I work on measuring the cosmological framework with supernovae (exploding stars) and Cepheids (pulsating stars). In 1998 I led a study for the High-z Team which provided the first direct evidence that the expansion of the Universe was accelerating and filled with Dark Energy. This study was the proverbial one which created more questions than answers! I followed this work with a number of studies to test the susceptibility of this measurement to contamination by unexpected types of dust or evolution. To this aim, I led the Hubble Higher-z Team beginning in 2002 to find 25 of the most distant supernovae known with the Hubble Space Telescope, all at redshift greater than 1. This work culminated in the first highly significant detection of the preceding, decelerating epoch of the Universe and helped to confirm the reality of acceleration by disfavoring alternative, astrophysically-motivated explanations for the faintness of supernovae. More recently I have turned my attention to improving the precision of our knowledge of the present expansion rate of the Universe, known as the Hubble constant. By measuring this quantity to within a few percent accuracy we can further constrain the properties of dark energy as well as the masses of neutrinos.

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Primary Section

Section 12: Astronomy

Secondary Section

Section 13: Physics