How giant magnetic fields are formed

Scientists have shown for the first time the occurrence of an instability in the interior of neutron stars that could lead to gigantic magnetic fields, possibly triggering dramatic explosions in the universe.

An ultradense ("hypermassive") neutron star is formed when two neutron stars in a binary system finally merge. Its short life ends with the catastrophic collapse to a black hole, possibly powering a short gamma-ray burst, one of the brightest explosions observed in the universe.

Short gamma-ray bursts as observed with satellites like XMM Newton, Fermi or Swift release within a second the same amount of energy as our galaxy in one year.

It has been speculated for a long time that enormous magnetic field strengths, possibly higher than what has been observed in any known astrophysical system, are a key ingredient in explaining such emission.

Scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) have now succeeded in simulating a mechanism which could produce such strong magnetic fields prior to the collapse to a black hole.

How can such ultrahigh magnetic fields-stronger than ten or hundred million billion times the Earth's magnetic field-be generated from the much lower initial neutron star magnetic fields?

This could be explained by a phenomenon that can be triggered in a differentially rotating plasma in the presence of magnetic fields: neighboring plasma layers, which rotate at different speeds, "rub against each other," eventually setting the plasma into turbulent motion.

In this process called magnetorotational instability magnetic fields can be strongly amplified.

This mechanism is known to play an important role in many astrophysical systems such as accretion disks and core-collapse supernovae.