Neutron star mergers are among the most extreme events in the Universe. A recent simulation shows that the cataclysm begins well in advance. Indeed, a chaotic ballet of their magnetic fields is engaged long before the final explosion, potentially challenging our perception of these titanic events.
These celestial objects form after a massive star explodes in a supernova. Their core then compresses into an object of incredible density, where a single teaspoon of matter would weigh millions of tons on Earth. Their magnetosphere also reaches a staggering power, exceeding that of our planet by several billion times.
Screenshot of a supercomputer simulation by NASA showing neutron stars spiraling before merger, creating magnetic chaos.
Credit: NASA's Goddard Space Flight Center/D. Skiathas et al. 2025 A team utilized NASA's Pleiades supercomputer. Their modeling recreated the final orbits before the collision, over a short sequence of 7.7 milliseconds. Thanks to this high resolution, scientists were able to observe the entanglement and non-linear evolution of the magnetic fields. According to the researchers, this approach requires colossal computing resources to capture such rapid phenomena.
Within these models, the magnetospheres behave like circuits in perpetual restructuring. Field lines link, break, and then reconnect, while electric currents race through the plasma at speeds approaching that of light. Such activity propels particles and generates emissions whose intensity fluctuates. The team noted that these mechanisms produce a great richness of optical signals.
The light from these stellar duos is not homogeneous; its brightness can change significantly. Consequently, what a distant observer detects greatly depends on their viewing angle. The signals gain power as the stars approach each other, influenced by the relative orientation of their magnetic poles. In the future, these fluctuations could facilitate the identification of such events with new telescopes.
These magnetic interactions could also imprint their signature in gravitational waves. Future observatories, such as the LISA space detector expected in the 2030s, could capture them. More sensitive than ground-based instruments, LISA will offer an unprecedented view of the Universe.
Neutron star collisions are also the forges of heavy elements like gold or silver, produced in explosions called kilonovae. By studying the stages preceding the merger, researchers hope to refine the interpretation of these phenomena and guide future observation missions.