A new simulation created using NASA’s supercomputers has shown how neutron star mergers can become difficult even before they collide. The magnetosphere, the most powerful magnetic field in the known universe, intertwines, creating chaos.
“Just before a neutron star collides, the highly magnetized, plasma-filled region around it, called the magnetosphere, begins to interact strongly,” team leader Dimitrios Skiasas, a researcher at NASA’s Goddard Flight Center, said in a statement. “We studied the last few orbits before the merger, where the entangled magnetic fields undergo rapid and dramatic changes, and modeled the potentially observable high-energy signals.”
Why are neutron stars so extreme?
When a star with approximately the same mass as the Sun runs out of hydrogen, the fuel it needs, nuclear fusion In the nucleus, the core collapses and the outer layer expands and is eventually lost. This causes the stars to end their lives as smoldering stellar embers called . white dwarf.
However, the situation is different for stars with masses more than about 10 times that of the Sun. When hydrogen-depleted nuclei collapse, the extra mass creates the pressure and temperature necessary to fuse the helium produced within these nuclei by millions of years of hydrogen fusion, forming even heavier elements.
This repeated process of fuel depletion, collapse, and reignition continues until the core of the massive star is filled with iron. When this final collapse occurs, a shock wave ripples through the star’s outer layers, which are blown away in a supernova explosion and take away most of the star’s mass.
The result is a stellar remnant filled with neutron-rich material packed into a space about 12 miles (20 kilometers) wide and one to two times the mass of the Sun. When this star’s core is rapidly shattered, it not only forms an incredibly dense object, but also generates a magnetic field. A thousand trillion many times stronger than Earth’s magnetosphere.
Massive stars are often found in binary pairs with a companion star, in which case when both stars die, a neutron star binary is formed. As the two dead stars swirl around each other, they create ripples in spacetime called gravitational waves, carrying away their angular momentum. This strengthens the neutron star binary. In other words, stellar remnants come closer together, emit higher-frequency gravitational waves, lose angular momentum more quickly, and are pulled together faster.
This phenomenon ends when the neutron stars get close enough to each other that their gravity overcomes them, and collisions and mergers inevitably occur. This triggers a burst of high-energy radiation called a gamma-ray burst (GRB), the last screech of gravitational waves, releasing a spray of neutron-rich material, a process that creates very heavy but unstable elements. These eventually decay to produce gold, silver, and other metals heavier than iron. This collapse also produces a glow that astronomers call a kilonova.
The fact that these events are responsible for the production of some of our most precious and important elements, as well as bright cosmic phenomena such as GRBs and kilonovas, means that there has been a major bias against studying the aftereffects of neutron star mergers.
Skiathas and colleagues took a different approach, looking more closely at what happens before neutron stars meet.
messy magnetism
To account for the 7.7 milliseconds before neutron stars merge, the researchers turned to the Pleiades Cluster Supercomputer at NASA’s Ames Research Center and created more than 100 simulations of a system of two neutron stars, each about 1.4 times the mass of the Sun.
“In our simulations, the magnetosphere behaves like a magnetic circuit that constantly rewires itself as the star orbits,” NASA Goddard team member Konstantinos Karapotarakos said in a statement. “The magnetosphere behaves like a magnetic circuit that constantly rewires itself as the star orbits. Magnetic field lines connect, break, and reconnect as electrical current surges through the plasma, which moves at nearly the speed of light. And rapidly changing magnetic fields can accelerate particles.” “To follow nonlinear evolution at high resolution, that’s exactly what we need a supercomputer.”
The team’s main goal was to investigate how the magnetic fields of these stellar remnants affect light, or electromagnetic radiation in technical terms, during the final orbits of neutron stars around each other.
Zorawar Wadiasingh, a team member from the University of Maryland, College Park and NASA Goddard, added in a statement. “Our study shows that the light emitted by these systems varies widely in brightness and is not evenly distributed, so a distant observer’s perspective on this merger is very important,” he added. “Also, depending on the relative magnetic orientation of the neutron star, the signal also becomes much stronger as the star gets closer and closer.”
The simulations revealed that the neutron stars’ respective magnetic fields are pushed out from behind as they orbit each other, causing the stellar debris to coalesce, then be destroyed and then recombined.
The researchers were also able to use the Pleiades star cluster to simulate how electromagnetic forces affect the surface of a neutron star. The goal of this study was to understand how magnetic stress builds up in such systems, but future modeling will be needed to determine what role magnetic interactions play in the final moments of neutron star merger.
“These behaviors may be imprinted in gravitational wave signals that can be detected by next-generation facilities,” team member and NASA Goddard researcher Demosthenes Kazanas said in a statement. “One of the values of research like this is that it helps future observatories figure out what they can see in both gravitational waves and light, and what they should be looking for.”
Using simulated magnetic fields, the researchers were able to identify the points at which the highest-energy emissions are produced and how these emissions propagate through the environment of a neutron star merger.
Researchers have discovered that the region around a neutron star merger produces high-energy gamma rays that cannot escape. That’s because individual particles of light, gamma ray photons, are rapidly converted into electron-positron pairs. But low-energy gamma rays, along with even lower-energy radiation like X-rays, were able to escape from neutron star mergers.
this means the future gamma ray Space telescopes, especially those with wide fields of view, could be used to detect signals from neutron stars on the verge of merging. Another way these systems can be studied before future mergers is through the detection of gravitational waves.
The Laser Interferometer Space Antenna (LISA), a NASA/European Space Agency project, could be particularly helpful in this regard. Scheduled to launch in the mid-2030s, LISA will be the first space-based gravitational wave detector to benefit from much higher sensitivity than the current generation of detectors on Earth, including the Laser Interferometer Gravitational-Wave Observatory (LIGO). The team’s results were published in the magazine on November 20, 2025. Journal of Astrophysics.