“There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened.”
-- Douglas Adams
I like that quote from The Hitchhiker's Guide to the Galaxy because in some sense, it really did happen that way. I remember being a graduate student at the University of Toronto, around the time when cosmologists were confident that they had figured out the Universe. The Hubble constant was well measured, giving a scale to the Universe. The matter content was the other important quantity to know. There was Dark Matter, sure, but it was detectable and still amounted to less than 30% of the energy content needed for the Universe to re-collapse. The Universe was believed to be open and would expand forever at an ever-slowing pace.
Then it happened: precise measurements of type Ia supernovae showed that the Universe was not slowing down, but speeding up! It was as if Adams’ notion of a new, bizarre Universe taking the place of our well-understood one actually happened. But, of course, it made for opportunities to research this new exotic beast: Dark Energy. That’s what I’m embroiled in right now, but I also have other interests as well...
Carnegie Supernova Project:
The Carnegie Supernova Project is attempting to provide independent constraints on the nature of Dark Energy by both improving the low-redshift sample of supernovae and constructing an I-band Hubble diagram for higher-redshift supernovae.
Gravitational Lensing of Polarized Sources:
My thesis work involved using the fact that the polarization angle of background sources is not changed by an intervening gravitational lens. If the polarization is aligned with the morphology of the background source, observed departures from this alignment directly measures the shear of the lens.
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•Kronberg, P.P et al., 1996, Estimates of the Global Masses of Two Distant Galaxies Using a New Type of Astrophysical Mass ``Laboratory'' (ADS)
Probing Interstellar HI clouds:
Distances in astronomy are always difficult to determine, but they are especially difficult with HI clouds. A group of graduate students (including yours truly) used the David Dunlap Observatory (DDO) to observe stars along the line of sight toward some Intermediate Velocity Clouds (IVCs). If the spectra of these stars showed sodium absorption blueshifted to the velocity of the cloud, we determined the star was behind the cloud. Lack of this absorption feature told us it was in front. Using spectroscopic parallax, we could bracket the distance to the IVC.