Physics Colloquium: Student Presentations
|Category:||College Of Engineering - Phy|
|Date & Time:||
from 02:00 PM to 03:00 PM
UMass Dartmouth Physics B.S. Student
Advisor : Robert Fisher
Title : "Simulating the Double-Degenerate Channel for Type Ia Supernovae"
Type Ia Supernovae (SNe Ia) are the thermonuclear explosions of white dwarfs, and are of fundamental importance to the study of the expansion of the universe and dark energy. For many years, it has been suspected that that SNe Ia occurred in binary systems, but the identity of the white dwarf’s companion could not be determined. A leading hypothesis, the single degenerate channel, suggests that a white dwarf may accrete matter from either a main sequence or red giant companion until it nears the Chandrasekhar limit of 1.4 solar masses. Another hypothesis is the double-degenerate channel, in which two white dwarf stars in orbit about one another detonate after merging together. A typical merged configuration consists of a central, rapidly spinning white dwarf, surrounded by a thick disk of remnant material, though it remains unclear precisely what the detonation mechanism of this merger is.
Recent observations of two supernovae discovered last year by the Palomar Transient Factory (PTF), SN 2011 fe and SN PTF11k, have provided evidence that suggest that both the SD and DD channels coexist in nature. However, the mechanisms by which the double-degenerate channel produce supernovae are poorly understood. Consequently, we seek to model the merger process with a smoothed-particle hydrodynamics code, GADGET.
UMass Dartmouth Physics B.S. Student Advisor : Robert Fisher Title : "Understanding the Origin of Binary and Multiple Stellar Systems: Determining Giant Molecular Cloud Core Fragmentation Criterion from Three-Dimensional Hydrodynamic Simulations of Star Formation in Supersonic Turbulence" Star formation occurs from the collapse of overdense, self-gravitating regions of giant molecular clouds (GMCs) called cores. It is thought that collapsing cores may develop nonlinear gravitational instabilities that lead to their fragmentation into two or more smaller collapsing regions, each of which may form a star. Many binary systems are thought to originate through this mechanism, called core fragmentation. However, the conditions under which core fragmentation occur are poorly understood. As most sun-like stars are found in binary systems, explaining this aspect of their formation is of great astrophysical interest. I investigate the conditions necessary for a star-forming core to fragment and produce a binary system instead of a single star. While previous efforts to determine these criteria worked with highly idealized models, I analyze a state-of-the-art hydrodynamical simulation in collaboration with Hubble Postdoctoral Fellow Dr. Stella Offner of Yale University, and Hubble Postdoctoral Fellow Dr. Kaitlin Kratter of the University of Colorado Boulder. The simulation depicts the evolution of individual star-forming cores within a larger 600 solar mass box of supersonic isothermal turbulence, 2 parsecs on a side. I use a dendrogram, or “tree-diagram,” algorithm, to identify structures, including cores, and their hierarchy. From this, I determine the properties of each core and will track their evolution over time. By contrasting the properties of cores that formed binary systems to those that formed single stars, I aim to derive a core fragmentation criteria.