Bulletin of the American Physical Society
APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022; New York
Session X13: Computational AstrophysicsRecordings Available
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Sponsoring Units: DAP Chair: Bernard Kelly, University of Maryland, Baltimore County Room: Empire |
Tuesday, April 12, 2022 10:45AM - 10:57AM |
X13.00001: Fully Dynamical General Relativistic SPH: Progress and Challenges Oleg Korobkin, Bing-Jyun Tsao, Hyun Lim, Irina Sagert, Wesley Even, Julien Loiseau The method of Smoothed Particle Hydrodynamics (SPH) has a lot of appeal for simulating variety of catastrophic astrophysical scenarios, such as mergers of compact objects, tidal disruptions, etc. SPH naturally refines dense areas and avoids vacuum without need for a “density floor”. With the recent detections of binary neutron star mergers GW170817 and GW190425 by the LIGO/Virgo collaboration, there is an increasing demand for better understanding of such mergers. Of particlar interest is the amount and composition of the neutron-rich matter ejected during the merger, as it harbors robust rapid neutron capture nucleosynthsis. Several previous works explored SPH with various degrees of approximations to general relativity, and a novel recent study proposed a fully dynamical relativistic SPH (Rosswog & Diener 2021). In this study, we explore another SPH approach to fully general relativistic dynamical geometry with a new code SPaRTA. It uses the Generalized Harmonic formulation of Einstein’s equations for evolving the dynamical metric. For the hydro, SPaRTA builds upon the fixed-metric SPH approach of Tejeda et al. (2017), generalizing it to time-dependent curvilinear geometries. We will discuss progress and challenges, and present several test problems. |
Tuesday, April 12, 2022 10:57AM - 11:09AM |
X13.00002: A Comparison of the SASI under Newtonian and General Relativistic Conditions Samuel J Dunham, Eirik Endeve, Anthony Mezzacappa, John M Blondin, Jesse L Buffaloe, Kelly Holley-Bockelmann After the collapse of a massive star, the newly formed shock stalls within the iron core. A contributing factor to the re-invigoration of the shock is a purely hydrodynamical instability known as the standing accretion shock instability (SASI). The SASI has been extensively studied in the context of Newtonian gravity and hydrodynamics (see, e.g., Blondin et al., 2003, ApJ, 584, 971; Foglizzo et al., 2006, ApJ, 652, 1436, Fernández 2015, MNRAS, 452, 2071), and has also been explored under general relativistic conditions with tabulated equations of state (Kuroda et al., 2016, ApJL, 829, L14). However, the true nature of the SASI, i.e., as a purely hydrodynamical phenomenon, has not been thoroughly investigated with a general relativistic treatment. We will discuss the results from a suite of simulations from thornado (Endeve et al., 2019 J. Phys.: Conf. Ser. 1225 012014), a high-order accurate radiation hydrodynamics code, comparing the SASI under conditions ranging from post-Newtonian to general relativistic regimes. By varying the mass of the proto-neutron star, the initial shock radius, and the mass accretion rate, we explore the impact that a general relativistic treatment has on the dynamics and evolution of the SASI. |
Tuesday, April 12, 2022 11:09AM - 11:21AM |
X13.00003: Detonation of a White Dwarf Star: Simulations of the Sub-Chandrasekhar Type Ia Supernovae Melissa A Rasmussen, Michael Zingale A type Ia supernova can result from the double detonation of a white dwarf star below the Chandrasekhar mass limit. Using the hydrodynamics code Castro, we simulate this detonation by perturbing a carbon/oxygen white dwarf with an accumulated shell of helium, with a small amount of nitrogen-14. In this work, we investigate the robustness of the model. Adjusting the location of the perturbation affects whether detonation occurs. Changing the composition of the helium shell affects the speed at which it burns. The size of the reaction network used affects whether the star's core burns immediately or from a shock wave from the shell. This last result is particularly notable, as it indicates that using reaction networks which leave out heavier elements may be an oversimplification, producing results with significant disparities from more thorough simulations. |
Tuesday, April 12, 2022 11:21AM - 11:33AM |
X13.00004: Turbulently-driven deflagration-to-detonation transition in near-Chandrasekhar mass white dwarfs Mark Ivan G Ugalino, Robert T Fisher, Alexei Y Poludnenko, Vadim N Gamezo Type Ia supernovae are luminous transients which enrich the interstellar medium with their nucleosynthetic products. They serve as crucial probes for observational cosmology, providing high-precision measurements of both the Hubble constant and cosmic acceleration. While multiple scenarios explaining type Ia supernovae have been proposed, a key physical process underpinning all channels is a detonation within the electron degenerate carbon-oxygen white dwarf interior. However, a first-principles understanding of how detonations are initiated in the turbulent conditions prevalent in SN Ia progenitors has remained elusive until now. In this work, we apply for the first time a laboratory-validated turbulently-driven deflagration-to-detonation (tDDT) mechanism to full 3D simulations of a near-Chandrasekhar mass carbon-oxygen white dwarf. We will present an analysis of the turbulently-driven flame propagation and characterize its local conditions at tDDT onset. We will also discuss the nucleosynthesis and the spectra that can be observed from tDDT-initiated type Ia supernovae events. |
Tuesday, April 12, 2022 11:33AM - 11:45AM |
X13.00005: Simulating Pure Deflagrations of Hybrid C/O/Ne White Dwarf Progenitors using FLASH Catherine Feldman, Nathanael Gutierrez, Samuel Boos, Nathan Adler, Donald Willcox, Dean Townsley, Alan C Calder Current simulations have yet to describe the entirety of the Type Ia supernova population, stellar explosions notably used as standard candles and inputs in cosmological parameter calculations. Pure deflagrations of white dwarf (WD) progenitors have been hypothesized to explain the dimmest of these, the subclass called Type Iax events, with hybrid C/O/Ne WDs producing some of the lowest ejecta masses and brightnesses. Using a state-of-the-art hybrid simulated with MESA as the input to a deflagration simulation in FLASH, we demonstrate that the coupling of this progenitor and ignition mechanism produce the expected bound remnant and ejecta, with unbound 56Ni yields consistent with observations. As this nonlinear problem is extremely sensitive to the initial conditions, we also test a range of ignition sizes and treatments of the stellar surface, to see how it affects the results. Finally, we discuss the challenges of simulating this subsonic incineration and expansion event, from choosing grid refinement criteria to analyzing the data. |
Tuesday, April 12, 2022 11:45AM - 11:57AM |
X13.00006: Particle Acceleration in Magnetically Dominated Plasma Turbulence Luca Comisso, Lorenzo Sironi Nature's most powerful high-energy sources are capable of accelerating particles to high energy on extremely short timescales, even shorter than the light crossing time of the system. It is yet unclear what physical processes can produce such an efficient acceleration, despite the copious radiative losses. By means of first-principles fully kinetic simulations, we show that strong turbulence in magnetically dominated plasmas generates a nonthermal particle spectrum with a hard power-law range within a few eddy turnover times. Low pitch-angle electrons can significantly exceed the nominal radiation-reaction limit, before abruptly cooling down. The electron energy spectrum becomes harder over time owing to particle cooling with an energy-dependent pitch-angle anisotropy. The resulting synchrotron spectrum is hard, with a significant fraction of radiative power emitted above the nominal radiation reaction limit. Our findings have important implications for understanding the nonthermal emission from high-energy astrophysical sources, most notably the prompt phase of gamma-ray bursts and gamma-ray flares from the Crab nebula. |
Tuesday, April 12, 2022 11:57AM - 12:09PM |
X13.00007: NR simulations of PPI-unstable BH-disk systems: Effect of magnetization at late times Erik K Wessel, Vasileios Paschalidis, Antonios Tsokaros, Milton Ruiz, Stuart L Shapiro Non-axisymmetric features in BH accretion disks are a sparsely-explored potential GW source. A natural channel for generating such features is the hydrodynamic Papaloizou-Pringle Instability (PPI). Previously, we conducted the first-ever study of the PPI around spinning BHs (a/M = 0.7), finding that BH spin can extend the signal lifetime and improve detection prospects by third-generation GW observatories. However, in a realistic scenario the material of these disks is likely to be magnetized. Prior studies have shown that the magneto-rotational instability (MRI) out-grows and surpresses the PPI during the early growth phase. Here we model a complementary scenario, where the PPI grows to its non-linear saturation state, and then the disk becomes magnetized in an MRI-suceptable configuration. This allows us to investigate, in full GR, a realistic non-axisymmetric configuration of magnetized matter which may concievably result from a number of formation channels. We find that the MRI once again attacks the non-axisymmetry and strongly reduces GW signal amplitude and lifetime. |
Tuesday, April 12, 2022 12:09PM - 12:21PM |
X13.00008: Understanding the Large Scale Poloidal Magnetic Field Dynamo in Black Hole Accretion. Frederick C Pardoe, Alexander Tchekhovskoy, Audrey Fung The production of relativistic jets by accreting black holes requires the presence of strong poloidal magnetic fields near the event horizon. However, most known physical processes are thought to strengthen magnetic fields in the toroidal directions. Recently, numerical GRMHD simulations were used to show that accretion disks with a purely toroidal magnetic field can create poloidal magnetic fields strong enough to launch jets via a large-scale dynamo (Liska et al. 2020). Prior to this analysis, it seemed likely that this dynamo functioned similarly to the alpha-omega dynamo, which generates poloidal fields in the Sun. In this presentation, I will summarize work that I conducted to determine the dynamo's mechanism. The dynamo creates four loops of alternating polarity. To determine if the alpha-process could account for these changes in polarity, I analyzed how the expansion, compression, and velocity of the fluid vary throughout the disk, and how they relate to each other. I found that changes in the expansion / compression and direction of motion of the fluid across different regions of the disk correspond to changes in loop polarity. However, these changes appear inconsistent with the alpha-process. Nonetheless, they provide strong clues to the dynamo’s actual mechanism. |
Tuesday, April 12, 2022 12:21PM - 12:33PM |
X13.00009: The black hole photon ring with AART: an Adaptive Analytical Ray-Tracing code Alejandro Cardenas-Avendano, Hengrui Zhu, Alexandru Lupsasca Horizon-scale observations of astrophysical black holes have initiated another chapter of strong-field studies of general relativity. As technological advances continue to improve our observations, it will become necessary to compare the resulting data against increasingly detailed theoretical predictions. In this talk, I will introduce a numerical framework that exploits the integrability of the Kerr spacetime and solves the null geodesic equation by evaluating elliptic functions, instead of direct numerical integration of the geodesic equations. We implement an adaptive non-uniform resolution for each lensing band (defined as the region in the image in which rays orbit a given number of times before arriving at the detector) suitable for detailed studies of the black hole photon ring. We demonstrate its computational performance by presenting black hole high-resolution movies of non-stationary and non-axisymmetric source profiles around Kerr black holes that can be computed on personal computers in less than five minutes. |
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