Professor of Physics & Astronomy
Ph.D., 1978 - University of Cambridge, England
Astronomy & Astrophysics
The main research interests of our group focus on astrophysical objects whose emission is generated by accretion onto a compact object. These include active galactic nuclei in which huge energy fluxes in all wavebands are generated by accreting supermassive black holes, cataclysmic binaries containing an accreting white dwarf, and X-ray binaries involving an accreting neutron star or a black hole (Picture of a BH binary). One of the fundamental problems in the theory of active galactic nuclei is the origin of the supermassive black hole and of the large amounts of material it has to swallow in order to produce the observed luminosities. Most galaxies are now thought to harbor supermassive black hole (See Hubble Space Telescope Evidence). Interesting and challenging problems of hydrodynamics, thermal and dynamical stability, and radiative transfer arise in the study of how this material loses its angular momentum, falls inward, and in so doing generates the observed radiation. In accretion-powered binary stars, different types of flow and physical conditions are encountered depending on whether the accreting compact degenerate object is a white dwarf or a neutron star, and on whether or not it has a strong magnetic field. The spectral characteristics, state of polarization, and time variability of the emitted radiation depend on the above premises. Modeling the properties of the observed radiation is currently an extremely active and lively field of research whose goal is the unraveling of the origin, structure, and evolution of compact short-period binaries and binary pulsars.
Current and Select Publications
- Patrick M. Motl, Juhan Frank, Joel E. Tohline, and Mario C.R. D'Souza, "The Stability
of Double White Dwarf Binaries Undergoing Direct Impact Accretion," submitted to Astrophys. J.
- Vayujeet Gokhale, Xiao Meng Peng, and Juhan Frank, "Evolution of Close White Dwarf
Binaries," Astrophys. J. 655, 1010-1024 (2007).
- P.M. Motl, J.E. Tohline, and J. Frank, "Angular momentum transport in double white
dwarf binaries," Prepared for the 6th International LISA Symposium, Greenbelt, Maryland,
19-23 June 2006. Published in AIP Conf. Proc. 873, 422-428 (2006). Also in Greenbelt 2006, Laser Interferometer Space Antenna, 422-428.
- Mario C.R. D'Souza, Patrick M. Motl, Joel E. Tohline, and Juhan Frank, "Numerical
simulations of the onset and stability of dynamical mass transfer in binaries," Astrophys.
J. 643, 381-401 (2006).