Supercomputer Reveals Millisecond Magnetar Birth in Neutron Star Collisions

Neutron star collisions do not always result in black holes. According to new supercomputer simulations, these violent mergers can produce magnetars—objects with extraordinarily powerful magnetic fields—in just a few milliseconds. This finding provides a potential explanation for the formation of some of the universe’s most magnetic entities.

Magnetars and Their Extreme Properties

Magnetars represent a rare subclass of neutron stars, characterized by magnetic fields roughly 1,000 times stronger than those found in ordinary neutron stars. These objects are linked to intense radiation bursts, including soft gamma-ray repeaters, and may also be responsible for generating certain fast radio bursts.

Simulating Collision Dynamics

Researchers utilized Japan’s FUGAKU supercomputer to model the collision of two neutron stars, each possessing 1.35 times the mass of the Sun. The simulation achieved a spatial resolution of 6.25 meters (20.5 feet), enabling the team to monitor small-scale turbulence and its impact on magnetic fields throughout the merger process.

The initial magnetic fields of the stars were set at approximately 3.16 trillion gauss, aligning with the upper range observed in binary pulsars. During the collision, fields reached around 10 quadrillion gauss across parts of the remnant, with localized areas exhibiting even greater strengths.

Turbulence and Field Amplification

The study highlights that "the Kelvin-Helmholtz instability that emerges when the two neutron stars touch amplifies the magnetic field to an expected electromagnetic saturation energy of ∼ 10⁵⁰ erg within 3 ms after the merger." This instability arises when adjacent fluid layers move at different velocities, creating turbulence that stretches and strengthens magnetic fields during the merger.

Initially, the strongest amplification occurs on very small scales. Subsequently, the turbulent magnetic field influences progressively larger regions of the merged star, allowing amplification to reach stellar scales. Researchers note that this instability "induces stellar-scale magnetic field amplification by at least a factor of 316."

Within approximately five milliseconds, the simulated stellar-scale magnetic field increased from 3.16 trillion gauss to around one quadrillion gauss, achieving magnetar strength. As the researchers stated, "Namely, a magnetar is born."

Survival and Future Evolution

While the simulation produced magnetar-strength fields, the researchers caution that uncertainties regarding turbulence and magnetic dissipation at extremely small scales could affect estimated amplification. In one extrapolation to more realistic conditions, the simulated stellar-scale field might be overestimated by a factor of 10. Even under this assumption, the resulting magnetic field would still reach approximately 100 trillion gauss.

The magnetic structure remained concentrated near the remnant’s equatorial plane rather than forming the organized polar field associated with launching relativistic jets. Additional magnetic processes, particularly the magnetorotational instability, may be required to develop that configuration.

The findings suggest that "a magnetar formation could be inevitable in binary neutron star mergers at least temporarily following the mergers, unless it promptly collapses to a black hole." The current simulations cover only the earliest moments after the collision. Longer calculations will be needed to determine how these magnetic fields evolve, whether they help power energetic outbursts, and how long the resulting neutron star can survive before potentially collapsing into a black hole.

The research, titled “A magnetar formation in binary neutron star merger,” was conducted by Kenta Kiuchi, Alexis Reboul-Salze, Yuichiro Sekiguchi and Masaru Shibata. It was published on June 9, 2026, on arXiv, with DOI: 2606.11299.