Dr. Jeremiah Murphy is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at the University of Washington. Dr. Murphy will complete development of BETHE, a multi-angle, multi-energy-group, multidimensional, time-dependent radiation-hydrodynamics code. Radiation hydrodynamics is a core subject in astrophysics, and for many phenomena asphericities either accompany or are fundamental to the underlying theory. BETHE uses novel mixed-frame radiation transport that is straightforward to implement, generalizable to multiple dimensions, accurate and relatively fast. The hydrodynamics solver is an Arbitrary Lagrangian-Eulerian (ALE) method and uses arbitrary grids providing flexibility to tailor the grid to the computational challenge. Together, these characteristics allow for unique multidimensional simulations of astrophysical phenomena. In particular, Dr. Murphy will (1) address the viability of the neutrino and acoustic mechanisms for core-collapse supernovae, (2) simulate winds from oblate hot stars, and (3) investigate whether proposed mechanisms for luminous-blue-variable outbursts can reproduce, in the context of rapidly rotating stars, the observations of Eta Carinae's Homunculus.
Dr. Murphy will also be actively involved with the Pre-Major in Astronomy Program (Pre-MAP), which seeks to retain a diverse student body in the University of Washington Astronomy Department. Pre-MAP targets first-year students from traditionally underrepresented groups in the sciences (women, first-generation and low-income college students, African Americans, Latinos, Native Americans, Southeast Asians and Pacific Islanders) with two primary goals: to engage students' interest and enthusiasm through research and to provide a supportive community, enabling their success. Dr. Murphy's roles will be to mentor Pre-MAP students, to offer simulation results to analyze, to support field trips and research, and, most importantly, to evaluate and improve the program.
With the support of the NSF Astronomy and Astrophysics PostdoctoralFellowship, I have advanced the theory of core-collapsesupernova explosions and helped the demographics of astronomy majorsto fairly represent the broader US demographic. A major challenge in stellar astrophysics is to understand how massivestars end their lives. The death of massive stars,core-collapse supernovae (CCSNe), are some of the most energeticexplosions in the Universe; they herald the birth of neutron stars andblack holes, are prodigious emitters of neutrinos and gravitationalwaves, influence the evolution of galaxies, trigger further starformation, and are a major site for the formation of the elements.Though these explosions play an important and multifaceted role inmany cosmic phenomena, the details of the explosion mechanism haveremained elusive for many decades. As a NSF AAP Fellow, I have developed a theoretical framework todescribe the conditions for successful SN explosions. Associated withthis theoretical framework, there are three major findings. In the first, I have investigated theconditions for successful explosions using computer simulations inwhich neutrinos stream from the newly formed neutron star and help tolaunch the explosion. More specifically, we find that explosionsensue if the neutrino power exceeds a critical threshold and that this criticalthreshold for explosions is lower in the presence of neutrino-drivenconvection. Therefore, a complete understandingof SN explosions requires a theoretical framework for the criticalneutrino power and the effects of neutrino-driven convection. As afirst step, we have developed a model for neutrino-driven convection.This model will enable a self-consistent theoretical approach toderiving the critical neutrino power for successful explosions and howconvection reduces it. In the second major finding, I have developed a model forgravitational wave (GW) emission from core-collapse supernovaexplosions. Because the explosion is initiated deep in the core ofthe exploding star, few observations are able to elucidate the physicsof the explosion mechanism. The detection of GWs by future detectorsoffers one of the few means to peer into the explosion mechanism. Ifthis model is correct, then the first detections of GWsfrom a SN will reveal the dynamics of explosion and offer importantinsights into the structure of neutron stars. Thirdly, we have developed a new method to determine the mass of thestar that exploded. Using Hubble Space Telescope images, wecharacterize the age of the stellar population surrounding thelocation of the SN. Since stars are born together this age reflectsthe age of the progenitor star before it exploded, and since moremassive stars burn their fuel faster and live shorter lives, the agegives a direct indication of the mass of the progenitor star. Ourprogenitor mass estimates provide important observational constraintson stellar evolution theory. As a broader impact, I worked to improve the diversity of astronomyundergraduate majors to more fairly represent the broader US demographics. A more diverse and inclusive scientific society would represent a moreequitable and vibrant scientific community. Although white males are only 35% of the US population, they account for 65% of the science, technology, engineering, and Mathematics (STEM) workforce.In contrast, women, minorities, and persons with disabilities make upalmost 70% of the total US workforce and 65% of theU.S. population, yet account for only 25% of the STEM workforce.These percentages indicate that the STEM workforce currently draws from a small portion of the US population,and this portion is projected to shrink to only 26.4% by 2050. Thesituation is exacerbated by the fact that the current STEM workforceis approaching retirement. If these demographic trendsin STEM continue, the future potential for science and engineering inthe US will suffer. Furthermore, the NSB report states that ``the number ofnative-born science and engineering (S&E) graduates entering theworkforce is likely to decline unless the Nation intervenes to improvesuccess in educating S&E students from all demographic groups,especially those that have been underrepresented in S&E careers.''For these two reasons, the 2003 NSB report concludes that the futurestrength of US S&E is at risk. In 2005, the Pre-Major in Astronomy Program (Pre-MAP) was developed inthe Astronomy Department of UW to increase retention of minoritiesduring the first crucial years. The two primary goals of Pre-MAP areto engage the student's interest and enthusiasm through research andto provide a supportive community. As a NSF Astronomy andAstrophysics Postdoctoral Fellow, I participated in this program in2008-2011. Some of my responsibilities included, but were not limitedto, mentoring undergraduates in research, providing funds for research,evaluating the program, and using organizational design methodologiesto help focus and restructure the program. A major finding of theseevaluations are that the Pre-MAP program has achieved a representativeand fair demographic.
