Magnetars can form from merging neutron stars, simulations suggest

High-resolution modelling on Japanese supercomputer shows how turbulent mixing can amplify magnetic fields 300-fold in milliseconds

By LineZotpaper

Published20 October 2026

Read Time2 min

A new study using the FUGAKU supercomputer in Japan has shown that magnetars - neutron stars with extraordinarily powerful magnetic fields - can be formed through the merger of two low-mass neutron stars. The simulations reveal that within milliseconds of contact, a turbulent instability in the neutron fluid dramatically amplifies the magnetic field, producing a star with a field more than 300 times stronger than the progenitors.

Most neutron stars have magnetic fields about 100,000 times stronger than the strongest fields created on Earth. About one per cent of them, however, are magnetars, whose fields can be another thousand times stronger, and are thought to power phenomena such as soft gamma-ray repeaters and fast radio bursts.

The new work, led by Kenta Kiuchi and published on the arXiv preprint server, investigates a formation channel for magnetars that has received less attention: the merger of two neutron stars that are each light enough that their combined mass stays below the Tolman-Oppenheimer-Volkoff (TOV) limit of about 2.6 solar masses. In such a case, instead of collapsing into a black hole, the merged object remains a single, more massive neutron star.

Using high-resolution simulations on the FUGAKU supercomputer, the team modelled identical low-mass neutron stars with initial magnetic field strengths of around 3 trillion Gauss - at the high end for typical neutron stars. Starting moments before collision and running to just after, the simulations showed that as the two stars make contact, the neutron fluid immediately enters a Kelvin–Helmholtz instability, a fluid-dynamic phenomenon familiar from the way a smooth stream of smoke rising from a candle becomes turbulent.

This instability mixes the neutron material so thoroughly and rapidly that the magnetic field is amplified dramatically throughout the merged star, reaching more than 300 times the initial strength within about a millisecond. The amplification is so fast that it may affect how the merger itself evolves and could alter the structure of the resulting neutron star.

The simulations were limited in that they assumed identical stellar masses and did not model further turbulence that could strengthen the field even more. Nevertheless, the authors conclude that the results demonstrate a clear path to magnetar formation through binary neutron star mergers.

Analysis

Why This Matters

Understanding how magnetars form is key to explaining the origin of fast radio bursts and soft gamma-ray repeaters, both of which are likely driven by these extreme magnetic fields.
Binary neutron star mergers are already detected by gravitational wave observatories; if some such events leave behind a magnetar rather than a black hole, the electromagnetic and gravitational wave signatures could differ in ways astronomers can look for.
The simulations show the process can happen on timescales of milliseconds, meaning magnetic amplification is not a slow afterthought but an integral part of the merger dynamics.

Background

Neutron stars are the ultra-dense remnants of supernova explosions, packing more than the Sun's mass into a city-sized sphere. Their magnetic fields are already extreme, but magnetars push that intensity a thousand times higher. The source of their extraordinary magnetism has been debated for decades. One long-standing idea is that a neutron star's magnetic field becomes amplified through the cooling and spinning-down of a young, rapidly rotating star. The new study adds a different route: direct formation from the merger of two relatively low-mass neutron stars. For this to happen, the combined mass must remain below the TOV limit, otherwise the merger forms a black hole.

Key Perspectives

Astrophysicists studying neutron stars: The rapid magnetic amplification via Kelvin–Helmholtz instability offers a clean, physically plausible mechanism that could explain at least some magnetars, especially those not associated with very young supernova remnants.

Gravitational-wave astronomers: The finding suggests that some merger events may produce a magnetar rather than an immediate black hole, which could produce a distinct electromagnetic counterpart - possibly a gamma-ray burst or a fast radio burst - in the aftermath.

Skeptics: The simulations assume identical masses and initial magnetic fields, an idealisation that may not reflect the diversity of real neutron star binaries. Further work is needed to test whether the mechanism holds under more realistic conditions and whether the field amplification can reach the trillion-Gauss levels seen in the most extreme magnetars.

What to Watch

Follow-up simulations that relax the assumption of identical stellar masses and include longer timescales to see how much stronger the field can become.
Gravitational wave detections of binary neutron star mergers where the total mass is close to the TOV limit - these are prime candidates to test whether a magnetar forms.
Observations of fast radio bursts and gamma-ray repeaters that are spatially coincident with a merger event, which would strongly support this formation channel.

Sources

A Magnetar Can Be Born When Two Neutron Stars Touch · Universe Today

Checked

12 claims in this story checked against 1 source: 9 supported.

Show each claim

SupportedMagnetars can form when neutron stars merge, according to simulations.Universe Today: “But it is clear that magnetars can form through mergers like this.”
SupportedThe modelling used the Japanese FUGAKU supercomputer and was high-resolution.Universe Today: “Using high-resolution simulations run on the Japanese supercomputer FUGAKU, the team looked at the merger of low-mass neutron star binaries.”
SupportedTurbulent mixing can amplify magnetic fields more than 300-fold within milliseconds.Universe Today: “As a result, the resulting magnetic field of the merged neutron star can be more than 300 times stronger than the initial magnetic fields. It ripples through the stars within about a millisecond”
SupportedThe study showed that mergers of two low-mass neutron stars can form magnetars.Universe Today: “But it is clear that magnetars can form through mergers like this.”
Partly supportedThe neutron fluid enters the Kelvin–Helmholtz instability immediately as the stars make contact.Universe Today: “within milliseconds after the two stars make contact, the neutron fluid within the region enters a Kelvin–Helmholtz instability.”
SupportedThe merged star’s magnetic field reaches more than 300 times the progenitors’ initial field strength.Universe Today: “the resulting magnetic field of the merged neutron star can be more than 300 times stronger than the initial magnetic fields.”
SupportedAbout 1% of neutron stars are magnetars, whose fields are about 1,000 times stronger than a regular neutron star’s field.Universe Today: “But about 1% of neutron stars have even stronger magnetic fields. Known as magnetars, their magnetic fields can be 1,000 times stronger than a regular magnetic field.”
Not in the sourcesThis merger formation channel for magnetars has received less attention than other channels.
SupportedTwo neutron stars whose combined mass is below the roughly 2.6-solar-mass TOV limit can merge into a single neutron star rather than a black hole.Universe Today: “If they happen to have a total mass less than the TOV limit, then they can merge and become a single neutron star.”
Partly supportedThe study was led by Kenta Kiuchi and published on arXiv.Universe Today: “Reference: Kiuchi, Kenta, et al. "A magnetar formation in binary neutron star merger." arXiv preprint arXiv:2606.11299 (2026).”
SupportedThe rapid amplification may affect how the merger evolves and the structure of the resulting neutron star.Universe Today: “it could play a role in how the merger progresses and could impact the structure of the resulting neutron star.”
SupportedThe simulations assumed identical stellar masses and did not include further turbulence that could strengthen the field more.Universe Today: “To simplify things a bit, they assumed stars with identical masses”