My graduate and postdoctoral research involved designing and constructing a cryogenic gravitational wave detector. While my primary research activities have moved to extragalactic astronomy and cosmology, I still have an interest in gravitational radiation and general relativity and occasionally do research in this area. In the last few years I have investigated the detectability of quanta of gravitation, i.e., gravitons, and my most recent publication is a conjecture that gravity may be an inherently classical phenomenon and that current efforts to quantize the gravitational field might be misplaced. I am also interested in the large-scale structure of the universe and in the "dark matter" and "dark energy" that are currently thought to comprise 96% of the energy content of the universe. One of the dramatic consequences of the presence of dark energy is that the expansion of the universe is accelerating rather than decelerating as expected if ordinary matter was the primary constituent of the cosmos. Several observations now support this conclusion. One is the expected correlation of the Cosmic Microwave Background (CMB) with distant gravitationally collapsing structures (the integrated Sachs-Wolfe or ISW effect). My collaborators and I have searched for this effect since the mid 1990's by comparing maps of the CMB with distant X-ray and radio wave tracers of matter. In 2003 (see our article in the January 2004 issue of Nature) we succeeded in finding convincing evidence for the ISW effect and thereby corroborated the accelerated expansion of the universe. Another related component of my research involves large-scale structure in the X-ray background (XRB). The XRB is composed primarily of active galactic nuclei, the energetic emissions due to matter accreting into supermassive black holes that lie at the centers of most galaxies. The clustering of these sources provides important information on the early formation of structure in the universe. A previous search for faint starlight that might trace the dark matter known to exist in galaxies, led to our observations of the diffuse intergalactic light (IGL) that exists in the regions between galaxies that are located in rich clusters of galaxies. This light is presumably due to stars that have been tidally stripped from individual galaxies as they move in the strong gravitational fields of the cluster. Careful characterization of the IGL provides important clues about the evolution of clusters of galaxies. The above image is from our observation of IGL in the rich cluster Abell 2029.
Undergraduate Involvement in Research
Many undergraduate astronomy and physics majors have had the opportunity to participate in the research projects described above as well as in others. Most of these have written senior theses based on their research, while others have presented their research at student symposia, and some students have coauthored papers in research journals.
I have taught many advanced undergraduate courses in astronomy and physics over the years including courses on: stellar structure, extragalactic astronomy, observational astronomy, general relativity, electromagnetic theory, and classical mechanics. In addition to standard introductory courses in physics and astrophysics, I routinely teach a freshman seminar in which physical science students investigate some of the current exciting topics in astrophysics