Gravitational Waves Unveil Thermal Secrets in Neutron Star Mergers

Scientists have used supercomputer simulations to study gravitational waves produced by merging neutron stars, revealing a correlation between the remnant temperature and wave frequency. These findings are significant for future gravitational-wave detectors, which will differentiate between models of hot nuclear matter. Credit: SciTechDaily.com

Simulations of binary neutron star mergers suggest that future detectors will distinguish between different models of hot nuclear matter.

Researchers used supercomputer simulations to explore how neutron star mergers affect gravitational waves, finding a key relationship with the remnant’s temperature. This study aids future advancements in detecting and understanding hot nuclear matter.

Exploring Neutron Star Mergers and Gravitational Waves

As two neutron stars orbit one another, they release ripples in spacetime called gravitational waves. These ripples sap energy from the orbit until the two stars eventually collide and merge into a single object. Scientists used supercomputer simulations to explore how the behavior of different models for nuclear matter affects gravitational waves released after these mergers. They found a strong correlation between the remnant’s temperature and the frequency of these gravitational waves. Next-generation detectors will be able to distinguish these models from each other.

Plots comparing the density (right) and temperature (left) of two different simulations of neutron star mergers (top and bottom) about 5 milliseconds after merger, as seen from above. Credit: Jacob Fields, The Pennsylvania State University

Neutron Stars: Laboratories for Nuclear Matter

Scientists use neutron stars as laboratories for nuclear matter in conditions impossible to probe on Earth. They use current gravitational-wave detectors to observe neutron star mergers and learn about how cold, ultra-dense matter behaves. However, these detectors cannot measure the signal after stars merge. This signal has information about hot nuclear matter. Future detectors will be more sensitive to these signals. Because they will also be able to distinguish different models from each other, this study’s results suggest that upcoming detectors will help scientists create better models for hot nuclear matter.

Detailed Analysis of Neutron Star Mergers

This research examined neutron star mergers using THC_M1, a computer code that simulates neutron star mergers and accounts for the bending of spacetimes, due to the strong gravitational field of the stars, and of neutrino processes in dense matter. The researchers tested thermal effects on the merger by varying the specific heat capacity in the equation of state, which measures the amount of energy needed to increase the temperature of neutron star matter by one degree. To ensure robustness of the results, the researchers performed simulations at two resolutions. They repeated the higher-resolution runs with a more approximate neutrino treatment.

References:

“Thermal Effects in Binary Neutron Star Mergers” by Jacob Fields, Aviral Prakash, Matteo Breschi, David Radice, Sebastiano Bernuzzi and André da Silva Schneider, 31 July 2023, The Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/ace5b2

“Identification of Nuclear Effects in Neutrino-Carbon Interactions at Low Three-Momentum Transfer” by 17 February 2016, Physical Review Letters.
DOI: 10.1103/PhysRevLett.116.071802

Funding: This research was primarily funded by the Department of Energy Office of Science, Nuclear Physics program. Additional funding was provided by the National Science Foundation and the European Union.

This work used the computational resources available through the National Energy Research Scientific Computing Center, the Pittsburgh Supercomputing Center, and the Institute for Computational and Data Science at The Pennsylvania State University.