Bulletin of the American Physical Society
APS April Meeting 2023
Volume 68, Number 6
Minneapolis, Minnesota (Apr 15-18)
Virtual (Apr 24-26); Time Zone: Central Time
Session U15: Mini-symposium: Multimessenger Astrophysics and Nuclear Physics IMini-Symposium
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Sponsoring Units: DNP DGRAV DAP Chair: Rebecca Toomey, Lawrence Livermore National Laboratory Room: Marquette VII - 2nd Floor |
Tuesday, April 18, 2023 1:30PM - 2:06PM |
U15.00001: Gamma-ray signatures from the radioactive decay of r-process nuclei Invited Speaker: Matthew R Mumpower The study of the rapid neutron capture or "r process" of nucleosynthesis offers the opportunity to glean insight into where the heavy elements (those above iron) on the periodic table are created in nature. Astrophysical sites, namely, supernovae and compact object mergers, e.g. two neutron stars, have long been touted as possible candidates. Gamma-ray spectra from nuclear decays offers unique potential as one of several multi-messenger components associated with these complex events. We report on gamma-ray studies in the late stages of an r-process event after neutron capture has completed and show that the treatment of nuclear isomers is critical to the resultant gamma-ray spectrum. |
Tuesday, April 18, 2023 2:06PM - 2:18PM |
U15.00002: Chemical Equilibration in Neutron Star Mergers Alexander Haber, Mark Alford, Jorge Noronha, Elias R Most, Ziyuan Zhang, Steven P Harris In this talk, we will explore the role of chemical equilibrium in dense matter and its potential influence on fluid dynamics in neutron star mergers. Chemical equilibrium refers to the establishment of steady-state particle fractions via weak decay processes. Rapid changes in temperature and density can drive fluid elements out of chemical equilibrium, and weak interactions can restore equilibrium on a timescale that can be comparable to the fluid flow dynamics. We will examine the possibility that chemical equilibration could affect the post-merger gravitational wave emission and leave observable signatures. |
Tuesday, April 18, 2023 2:18PM - 2:30PM |
U15.00003: On the Prospects for R-Process Nucleosynthesis in Realistic GRRMHD Collapsars Brandon L Barker, Jonah M Miller, Benjamin Ryan We model a black hole – accretion disk system originating from the circularization of in-falling matter from a collapsing star – the collapsar scenario. We use the new, open source code Phoebus which includes frequency dependent general relativistic radiation magnetohydrodynamics with a dense matter equation of state. Using these improved initial conditions, we access the prospects for rapid neutron capture (r-process) nucleosynthesis occurring in the collapsar disk winds. Moreover, we access whether or not these winds may escape the in-falling stellar mantle and carry away r-process rich ejecta. We present prospects for future work on the sensitivity of these results to properties of the progenitor star. |
Tuesday, April 18, 2023 2:30PM - 2:42PM |
U15.00004: Transuranic fission fragments in stars and prospects for multi-messenger astrophysics Ian Roederer I will summarize the evidence that fission fragments of transuranic elements have been detected among the abundance patterns of r-process-enhanced stars. A meta-analysis of 42 r-process-enhanced stars reveals that the elements Ru, Rh, Pd, and Ag (atomic numbers 44 ≤ Z ≤ 47, mass numbers 99 ≤ A ≤ 110) exhibit a correlation with abundances of heavier elements (63 ≤ Z ≤ 78, A > 150) that is not shared by their immediate neighbors (34 ≤ Z ≤ 42 and 48 ≤ Z ≤ 62). Coproduction via fission fragments of transuranic nuclei provides the most compelling explanation for this behavior. This signature provides the first evidence that neutron-rich fissioning nuclei with A > 260 are produced in r-process events. Finally, I will discuss prospects for detecting transuranic nuclei in multi-messenger observations of merging pairs of neutron stars and the kilonova events that accompany them. |
Tuesday, April 18, 2023 2:42PM - 2:54PM |
U15.00005: Impact of thermal pions on the bulk viscosity of nuclear matter Steven P Harris, Sanjay K Reddy, Bryce Fore Weak interactions in the dense nuclear matter in neutron stars give rise to a bulk viscosity which leads to damping of the density oscillations that naturally occur when two neutron stars merge. If nuclear matter consists of just neutrons, protons, and electrons, the Urca processes are the relevent equilibration process, and it has been shown that they can dissipate significant amounts of energy on millisecond timescales. It is expected that in dense matter at the high temperatures encountered in neutron star mergers, a thermal population of pions will be present. If so, then both the Urca processes and various pion decay and production processes give rise to bulk viscosity as they attempt to restore beta equilibrium. We find that the bulk viscosity in matter containing a thermal population of pions is enhanced by up to an order of magnitude compared to the pionless case. |
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