Dr. Peter Bodenheimer

Professor of Astronomy and Astrophysics

Office: 335 Interdisciplinary Sciences
Phone: 831-459-2064
Email: peter@ucolick.org

Educational Background:

Research Interest:

Peter Bodenheimer's general interests are in theoretical astrophysics, particularly in numerical calculations of stellar evolution and the formation of giant planets and in hydrodynamic calculations of the collapse of protostars and the formation of stellar binary and multiple systems. He has also worked on the physics of the interstellar medium, involving the numerical calculation, in two space dimensions, of the evolution of H II regions and supernova remnants, and their influence on molecular clouds, globular clusters, and dwarf galaxies. Recent work in connection with stellar evolution involves numerical calculations, primarily in two space dimensions, of the common envelope phase, during which a companion star spirals in through the envelop of a red giant, eventually forming a close binary system and generating enough energy to eject the hydrogen-rich envelope of the giant.

His major research at present is closely related to questions of the origins of planetary systems. He has done work on several aspects of this problem, including the collapse of protostars and the disk formation phase, the evolution of the disk under the influence of viscosity, detailed calculations of the buildup of giant planets in the disk, and calculations of the evolution of the central star. A particular calculation, in collaboration with Greg Laughlin and Harold Yorke, starts from an initial condition representing the core of a molecular cloud and follows the collapse of a rotating protostar, including the effects of radiative transfer and of viscosity once the disk has formed. Detailed frequency-dependent radiative transfer calculations are performed on selected models, so that the emergent continuous spectral energy distribution can be determined--as a function of time and of viewing angle with respect to the rotation axis--and compared with the observed spectra of some suspected protostellar sources. The results of these axisymmetric calculations indicate that the disk is relatively massive compared with the mass of the central star. It is found to be gravitationally unstable to nonaxisymmetric perturbations; this instability is likely to be a key to its further evolution. The equilibrium structure of the disk is used as input to a three-dimensional hydrodynamical code based on the smoothed-particle method. A pattern of traveling spiral arms is set up in the disk, which results in transfer of mass inward onto the central star and transfer of angular momentum outward. The disk evolves on a timescale of several hundred thousand years toward a configuration with more mass in the central object and less in the disk; this pattern is consistent with the probable evolution of our solar system.

Over the last 20 years he has also been involved in various projects to calculate the full three-dimensional collapse of rotating protostars with numerical codes, with a view toward studying the formation of binary and multiple stars; he has published review articles on that topic in both Protostars and Planets III and IV. He has worked on a variety of other projects concerning various phases of hydrodynamic and hydrostatic stellar evolution, including the long-term evolution of low-mass stars, and the first detailed numerical study of supernova core collapse with rotation. Further work includes structure and evolution of protoplanetary disks. He has been one of the Co-PI's in the Center for Star Formation Studies, a collaboration of theorists at UC Santa Cruz, NASA-Ames Research Center, and UC Berkeley funded by the NASA Astrophysical Theory Program, from 1986 to 2003.

Dr. Bodenheimer's work on planet formation started in about 1974. He was one of the first to calculate hydrostatic and hydrodynamic evolution of giant planets, in spherical symmetry using an adapted stellar evolution code, initially under the assumption that they formed as gravitationally bound gaseous subcondensations in the solar nebula. This work then developed into a collaboration, centered at NASA-Ames, which was based on the core accretion - gas capture scenario for giant planet formation. Calculations now include planetesimal accretion to form the rocky core, the accretion and evolution of the gas in the envelope, and the interaction, ablation, and evaporation of planetesimals as they pass through the envelope. Recent work has focussed on the problem that the formation time according to this mechanism is longer than likely gaseous disk lifetimes. Reasonable and verifiable changes in the physics assumed in the calculations can in fact reduce the accretion time for the gaseous envelope, once the core is formed, to times comparable to or shorter than disk lifetimes. There still may be a problem regarding the accretion time of the core, but including the effects of the gaseous envelope increases the cross section for accretion of solid particles. He has also done a number of evolutionary calculations for extrasolar giant planets. The well-known Nature paper with Lin and Richardson shows how the unexpected discovery of a giant planet very close to its star can be explained by orbital migration of the planet after its formation. Other numerical calculations account for the formation of the two giant planets in the 47 Uma system. A calculation with Lin and Laughlin showed for the first time that the radius of the newly discovered transiting planet OGLE TR-56b is consistent with theoretical models. Other work shows that the planet transiting HD 149026 must have a large component of heavy elements, which could be in a core of up to 70 earth masses. Some of the work on these topics is summarized in his review article in Annual Review of Earth and Planetary Sciences in 2002.