Who am I?

In May 2002, I left the Whitehead to join CombinatoRx, Inc, a pharmaceutical company that is seeking optimal combinations of drugs to treat cancer, inflammatory and infectious diseases. At CombinatoRx, I'm heading the computational biology team, where, among other things, I've been exploring the utility of our combination screens for systems biology applications. I also hold an adjunct faculty position at Boston University's Biomedical Engineering department.

From 1985 to 2000, my astronomy work was focused mostly on observational cosmology, in the context of gravitational lensing.

Gravitational lensing happens when a distant galaxy has another "lensing" galaxy in front of it.  Gravitational lensing directly probes the mass distribution of distant galaxies, yielding important constraints on dark matter. Gravitational lensing relies on chance alignments (the lens must lie within about 1/3600 degree from the line of sight to the source), and is extremely rare. After 20 years of searching, there are only about 70 known examples of galaxy-galaxy lensing. Here's a picture of how I would look through a gravitational lens.

I have worked on the following projects:

• Time Delay in Q0957+561. We monitored the first known lens in the radio and measured a delay in the signals between the two images. This gives a direct distance estimate to the lensing galaxy which is completely independent of the usual distance ladder (see, for example, the first and the most recent articles).
• Gravitational Lens Searches. In the MIT-Greenbank-VLA survey, we observed 4000 radio sources using the VLA, and found six lenses (about a third of the known sample at the time). My favourites are MG1549+3047 and MG0751+2716. I also conducted a novel search for gravitationally lensed radio lobes, which makes very efficient use of observing resources.
• Hubble Space Telescope Lens Survey. Our CASTLES survey observed all known galaxy-mass lenses to obtain better lensing constraints and detailed information on the lens galaxies, as well as the host galaxies of the background sources. At its height, CASTLES received 2% of the HST observing schedule. Here are the first survey article and some nice pictures.
• Radio-Quiet Quasars. Most quasars (very active galaxy centers) are very faint in the radio, and it is disputed whether they are powered by a black hole, like their radio-loud cousins are believed to be, or by a massive burst of star formation. The radio variability could yield crucial information on this question, and can also give a better understanding of gravitationally-lensed RQQs. We have monitored ~25 RQQs using the VLA, and are finding some interesting results.

I have also taught sections of introductory astronomy and physics courses, most recently for the Core program at Harvard. You can see some selected notes I prepared for my students on relativity and quantum mechanics.