NASA scientists say new supercomputer simulations are offering a detailed look at tangled magnetospheres around merging neutron stars just before impact, and the work points to possible light signals future observatories could detect. The simulations focus on the last orbits before two city-sized neutron stars collide, when magnetic fields and plasma can rapidly rearrange in ways that may produce high-energy emission.
Lead scientist Dimitrios Skiathas said the team studied “the last several orbits before the merger,” modeling how “entwined magnetic fields undergo rapid and dramatic changes” and what signals might be observable. The research is described in a paper published Nov. 20, 2025, in The Astrophysical Journal, according to NASA.
What the simulations show
In NASA’s description, the magnetospheres are plasma-filled regions around neutron stars, and they begin interacting strongly just before the stars merge. The NASA visualization page describes magnetic field lines that can connect the two stars, break, and reconnect, while currents surge through plasma moving at nearly the speed of light.
Co-author Constantinos Kalapotharakos compared the simulated magnetosphere to “a magnetic circuit that continually rewires itself as the stars orbit,” with field lines repeatedly connecting and reconnecting as conditions change. The NASA visualization page also shows simulated views from different angles, describing how brightness and direction of electromagnetic emission can vary as the merger progresses.
Why pre-merger light matters
Neutron star mergers are linked to a type of gamma-ray burst (GRB), which NASA describes as the most powerful class of explosions in the cosmos. NASA notes that these events can involve near-light-speed jets that emit gamma rays, gravitational waves, and a kilonova explosion that forges heavy elements like gold and platinum.
NASA also says only one event observed in 2017 has been seen to connect all three phenomena—gamma rays, gravitational waves, and a kilonova—so far. In the YouTube narration for the project, NASA Goddard adds that astronomers want to find these systems before they collide, and the new simulations are meant to guide what to look for.
How the models were built
NASA says the simulations were performed on the Pleiades supercomputer at NASA’s Ames Research Center in California’s Silicon Valley. The NASA story says the team ran more than 100 simulations of two orbiting neutron stars, each with 1.4 solar masses, while the NASA visualization page describes the team running “hundreds of simulations” of the same type of system.
According to NASA, most of the simulations capture the last 7.7 milliseconds before the merger, allowing close study of the final orbits. Separately, the NASA visualization page describes a simulation sequence starting about 0.03 seconds before the stars’ surfaces come into contact, with an example view showing the stars 34 miles (54 kilometers) apart at the start of the video.
NASA says neutron stars can pack more mass than the Sun into a ball about 15 miles (24 kilometers) across. NASA also states that newborn neutron stars can spin dozens of times per second and can have magnetic fields up to 10 trillion times stronger than a refrigerator magnet.
What signals could escape
NASA says the simulations helped identify where the highest-energy emission would be produced and how it would propagate through the surrounding plasma. The NASA story says the highest-energy gamma rays—described as having energies trillions of times greater than visible light—would likely not escape because they quickly convert into particles in the presence of strong magnetic fields.
However, NASA says lower-energy gamma rays, with millions of times the energy of visible light, could exit the system, and related particles may radiate at still lower energies, including X-rays. Co-author Zorawar Wadiasingh said the simulated light can vary widely in brightness and is not evenly distributed, meaning a distant observer’s viewing angle could strongly affect what is detected.
What comes next for observatories
NASA says the results suggest future medium-energy gamma-ray space telescopes—especially with wide fields of view—could potentially detect pre-merger signals if gravitational-wave observatories provide timely alerts and localization. NASA notes that current ground-based facilities such as LIGO in Louisiana and Washington and Virgo in Italy detect neutron star mergers in the 10 to 1,000 hertz range and can support rapid electromagnetic follow-up.
NASA also says ESA and NASA are collaborating on LISA (Laser Interferometer Space Antenna), a space-based gravitational-wave observatory planned for launch in the 2030s, to observe neutron-star binaries earlier in their evolution at lower frequencies than ground-based detectors. Goddard’s Demosthenes Kazanas said magnetic behavior could be “imprinted on gravitational wave signals” detectable in next-generation facilities, helping researchers understand what future observatories should be looking for in both light and gravitational waves.
