Research Interests

Black Holes in Galaxy Centers

I work in collaboration with The Nuker Team to study the centers of galaxies in an attempt to understand the relationship of galaxy nuclei to supermassive black holes that may have once powered quasars. We think we have shown that black holes that once powered quasars are a common feature of nuclei of normal galaxies. You can read our Nature Review article in postscript here. The photo at right is a quasar in an interacting galaxy imaged by Bahcall, Kirhakos, Schneider and Saxe with HST. A controversial view of the history of black hole formation in the universe is illustrated here.

Spacecraft Detection of Gravitational Waves

An interesting related problem is the history of mergers of galaxies and of massive black holes in the universe. The Laser Interferometric Space Array (LISA) , is a proposed constellation of Laser Doppler-ranging spacecraft that will be able to detect gravitational radiation from merging black holes in our past lightcone to redshifts of 3 or more. The science payoffs from the proposed LISA mission are summarized by Sterl Phinney here.

Formation and Evolution of Clusters of Galaxies

Another major interest is the formation and dynamics of clusters of galaxies. In the past Avi Loeb, Ed Turner and I argued that that the cosmolgy would be reflected in the history of cluster formation and hence in the prevalence of substructure in clusters. More recently Mary Crone, Gus Evrard, Joe Mohr and I have looked at cluster structure in detail. The history of the rate of cluster formation is shown as a function of time on the right in different density cosmologies (see Astrophys J, 393,477)./

Since I wrote my Ph.D. dissertation on cluster dynamics in '75 it remains a keen interest.

Other Interests

Gravitational lenses, estimation of cosmological parameters (take a look at this provocative paper), dynamics and evolution of galaxies. This is a particularly interesting cluster of galaxies acting as a gravitational lens .

A complete scientific bibliography is here.