Simulation Shows Two Neutron Stars Merging Into a Magnetar in Milliseconds

A computer simulation suggests that when two lighter-than-usual neutron stars collide, the fluid at the contact point becomes turbulent and can boost the magnetic field more than 300 times, Universe Today reported. The result points to a way that magnetars, the most strongly magnetized stars known, may be born.

The work is a simulation study posted as a preprint on arXiv by Kenta Kiuchi and colleagues. It shows that such a merger can produce a magnetar, and it shows how fast the field grows. It does not describe an observed event.

What magnetars are and why their origin is a puzzle

Every neutron star has an intense magnetic field. According to Universe Today, a typical one is about 100,000 times stronger than the strongest fields people can create on Earth. About 1% of neutron stars go further. These magnetars can have fields 1,000 times stronger than a regular neutron star field.

Magnetars are considered a likely source of powerful short-lived events, including soft gamma-ray repeaters and fast radio bursts. How they form has been an open question, and the new study tests one route.

Why most neutron star mergers do not end this way

When two neutron stars collide, the usual result is a black hole. Universe Today explained that this happens when their combined mass exceeds a threshold known as the Tolman-Oppenheimer-Volkoff limit, which is around 2.6 solar masses.

Some neutron stars are lighter than most. If a pair together falls below that limit, they can merge into a single neutron star instead of collapsing. The team focused on that case.

What the simulation showed

The researchers used the Japanese supercomputer Fugaku to run high-resolution simulations of low-mass neutron star pairs. To keep the problem manageable, they gave both stars identical masses and otherwise typical properties. They set each star's magnetic field at around 3 trillion Gauss, which is toward the upper end for typical neutron stars. The simulations covered the period from just before the stars touch to just after.

Within milliseconds of contact, the neutron fluid in the contact region develops what physicists call a Kelvin-Helmholtz instability. In plain terms, a smooth flow turns chaotic and swirling, much like the rising stream of smoke from a candle that has just been blown out.

In the simulations, this turbulence mixed the neutron material thoroughly and quickly. It dragged the magnetic field along with it as the mixing spread through the rest of the merged object. The resulting field was more than 300 times stronger than the starting fields. Universe Today noted that further turbulence might strengthen it even more, but that lies beyond what this simulation can capture.

Why it matters

For general readers, this is a story about how some of the most extreme objects in the universe come to exist. The finding does not affect daily life, but it ties together several things astronomers observe. Magnetars are linked to bursts of gamma rays and radio waves, and a merger route gives researchers a concrete process to look for.

The speed of the effect is also notable. According to Universe Today, the field amplification spread through the stars in about a millisecond. That suggests it could influence how the merger itself unfolds and shape the structure of the neutron star that results.

What remains unknown

This is one set of simulations built on simplifying assumptions, including equal-mass stars and a single starting field strength. It is a preprint, so it is a single result and not a settled conclusion. Universe Today said more study is needed to learn exactly how the process plays out, though it described the finding as clear evidence that magnetars can form through mergers of this kind.

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Around Prague, based on reporting by Universe Today