Dr. David Dearborn, an astrophysicist from Lawrence Livermore National Laboratory, visited SCSU March 16-19, 2005. His visit was part of a collaboration with Dr. Jennifer Cash of the Department of Biological and Physical Sciences at SCSU. This collaboration is through the Lawrence Livermore National Laboratory's Research Collaborations Program for Historically Black Colleges and Universities. Dearborn and Cash study stars using computer modeling to simulate their physical properties. During his visit Dr. Dearborn delivered several talks that were cohosted by SCSU's Department of Social Sciences and the Department of Biological and Physical Sciences.
The following two talks were open to the public on Thursday evening in the Barbara Ann Vaughan Recital Hall, Fine Arts Center on the SCSU Campus.
As children of the sun god, Inti, the Inca ruled their empire, and Skywatching activity was used to support their elite position in the cosmos. They held ceremonies involving a system of solar markers around the horizon of Cuzco in which the sun appeared to participate. The remains of such solar markers have now been found, giving flesh to early Spanish accounts and showing how society was stratified. This system required the support of other observations, and important clues as to who made these supporting observations were found at Machu Picchu.
The evidence for the threat level of an asteroid collision is surveyed along with the accuracy to which orbits can be determined. Accuracy limits the time over which orbits are well enough known to predict a collision, and so sets the time available for any mitigation technology to operate. With this information, the systematic requirements to divert an object on an earth-impacting course are found and compared to current technologies.
The final talk, held Friday at Noon in Hodge Hall, was open to SCSU faculty and students.
Stars provide the fundamental quantitative units for measuring the universe. They set the scale(s) for determining distances, provide the best limits on age, and drive the chemical evolution. Stars have also been used as physics laboratories, providing useful constraints in atomic, nuclear, and particle physics. To date, almost all modeling of stars has been one-dimensional, an approximation that rigorously applies only to a minority of stars. Even in spherical (single) stars, the models are dependent on approximating complex three-dimensional (3-d) processes like convection. To improve this limitation, we have constructed Djehuty, a 3-d stellar evolution/structure code that operates on massively parallel machines with the best available physical data (Opacities, EOS, etc.) as well as new algorithms.
This code has been applied to a number of astronomical situations. In this presentation we will present work in progress on understanding the long-standing problem of core convection and overshoot on the main sequence. Recent results will also be presented on the helium flash, an important stage of evolution that is little studied, as it is numerically difficult to model and critically dependant on the time development convection. Finally, results will be presented from modeling a new supernova mechanism as the possible explanation of the remnant, Sgr A East. In it we examine the compression of a white dwarf that results from penetration of a star into a strong gravitational potential (a GR effect). For large black holes (M > 1000 solar masses), compression dominates over the tidal effect (for a white dwarf sized object), and can ignite the star.
Dr. Dearborn's visit was described in this Times & Democrat article.