Month: March 2025

Unraveling the Origins of Rare Gamma-Ray Bursts and Kilonovae

This figure shows how the composition of matter (color map) and magnetic field lines (blue streamlines) evolve over time in different simulation models. Each column represents a different moment in time, while each row corresponds to a different strength of the magnetic field. The weakest magnetic field case is not shown because it looks nearly identical to the next one.In these simulations, neutron-rich material is ejected from the system when powerful magnetic winds accelerate it before it reaches a stable state. As seen in the figure, when the magnetic field is strong enough, low-electron-fraction (low-Ye) material can be pushed outward and escape from the disk region. The images also reveal a clear relationship between the patterns of matter distribution and the structure of the magnetic field, showing how magnetism shapes the flow of material in these extreme environments.
This figure shows how the composition of matter (color map) and magnetic field lines (blue streamlines) evolve over time in different simulation models. Each column represents a different moment in time, while each row corresponds to a different strength of the magnetic field. The weakest magnetic field case is not shown because it looks nearly identical to the next one.
In these simulations, neutron-rich material is ejected from the system when powerful magnetic winds accelerate it before it reaches a stable state. As seen in the figure, when the magnetic field is strong enough, low-electron-fraction (low-Ye) material can be pushed outward and escape from the disk region. The images also reveal a clear relationship between the patterns of matter distribution and the structure of the magnetic field, showing how magnetism shapes the flow of material in these extreme environments.

We have conducted the first-ever seconds-long 2D simulations of a rare astrophysical event known as accretion-induced collapse (AIC) in rapidly spinning, highly magnetized white dwarfs. These events, which may arise from white dwarf mergers, could be responsible for generating powerful relativistic jets and neutron-rich outflows.

Our findings suggest that, under extreme conditions, AIC could produce long gamma-ray bursts (LGRBs) accompanied by kilonovae, similar to rare events like GRB 211211A and GRB 230307A. These results also support the idea that AIC may play a role in creating the heavy elements formed through the r-process, enriching the universe with elements like gold and platinum.

While these simulations provide exciting insights, longer 3D simulations are needed to fully understand the behavior of magnetic fields and energy transport in these extreme environments.

Read more in our published paper in Astrophysical Journal Letters.

BNS_NURATES: Advancing Neutrino Physics in Neutron Star Mergers

This image shows how neutrinos escape from a merging binary neutron star system, depending on their energy and how they interact with matter. The colored background represents the density of matter, while the dashed red and solid green lines outline the regions where neutrinos of different energies last interact before freely streaming away. The two sets of lines compare different ways of modeling neutrino absorption, with the green lines including additional physical effects like weak magnetism and nucleon decays. The left panel focuses on electron neutrinos, while the right panel shows electron antineutrinos. The different shades of color correspond to neutrinos of increasing energy, from 3 to 25 MeV, with higher-energy neutrinos escaping from deeper regions.
This image shows how neutrinos escape from a merging binary neutron star system, depending on their energy and how they interact with matter. The colored background represents the density of matter, while the dashed red and solid green lines outline the regions where neutrinos of different energies last interact before freely streaming away. The two sets of lines compare different ways of modeling neutrino absorption, with the green lines including additional physical effects like weak magnetism and nucleon decays. The left panel focuses on electron neutrinos, while the right panel shows electron antineutrinos. The different shades of color correspond to neutrinos of increasing energy, from 3 to 25 MeV, with higher-energy neutrinos escaping from deeper regions.

Understanding the role of neutrinos in binary neutron star (BNS) mergers is essential for building accurate models of these extreme cosmic events. To help tackle this challenge, we introduce BNS_NURATES, a new open-source library designed to improve the precision and realism of neutrino interactions in simulations.

BNS_NURATES enhances existing methods by incorporating key microphysics effects, such as weak magnetism and mean field corrections, which influence how neutrinos interact with matter. It also accounts for inelastic neutrino scattering and (inverse) beta-decays, providing a more complete picture of how energy and momentum are exchanged in the system.

As a first test, we applied BNS_NURATES to data from a neutron star merger simulation. Our results reveal how these additional effects can alter neutrino emission and transport, potentially impacting the physics of kilonovae and gravitational wave signals. These results, as well as a detailed description of the library are described in a paper in press on Physical Review D.

By making BNS_NURATES open-source, we aim to provide the astrophysics community with a powerful new tool for studying neutron star mergers and their role in the galactic chemical evolution.

Performance-Portable Binary Neutron Star Mergers with AthenaK

Rest mass density, temperature, and magnetic field strength in a binary neutron star merger simulations performed with AthenaK. The two neutron stars have a mass of 1.3 solar masses (each) and the matter is described using the SFHo equation of state.
Rest mass density, temperature, and magnetic field strength in a binary neutron star merger simulations performed with AthenaK. The two neutron stars have a mass of 1.3 solar masses (each) and the matter is described using the SFHo equation of state.

We are excited to introduce a major upgrade to AthenaK, a cutting-edge computational tool used to study black holes, neutron stars, and the extreme physics of magnetized fluids in curved spacetime. Our latest extension enables AthenaK to handle dynamically evolving spacetimes, a crucial capability for simulating events like neutron star mergers and accretion disks around black holes.

With advanced numerical techniques, AthenaK maintains high accuracy and efficiency, even in the most challenging astrophysical scenarios. Our new solver was rigorously tested and compared with existing methods, showing strong agreement in key simulations. Notably, we have achieved the first-ever published neutron star merger simulations running on GPUs, maintaining remarkable precision in mass conservation.

AthenaK is built for the next generation of supercomputers, achieving exceptional scaling on the Frontier supercomputer, where it efficiently utilizes tens of thousands of GPUs. This advancement represents a significant step forward in numerical relativity, making it possible to explore the most extreme cosmic events with unprecedented speed and accuracy.

Our results are described in this paper, published on the Astrophysical Journal Supplement Series.

Stay tuned for more exciting discoveries enabled by AthenaK!