Scientists have now succeeded in simulating a mechanism which could produce strong magnetic fields prior
to the collapse to a black hole.
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.
An ultra-dense ("hypermassive") neutron star is formed when two neutron stars in a binary system finally merge.
The incredibly strong magnetic fields of some neutron stars can rip the stars open (Illustration: NASA)
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.
How can such ultra-high magnetic fields -- stronger than ten or hundred million billion times Earth's
magnetic field -- be generated from the much lower initial neutron star magnetic fields?
Numerical simulations conducted by scientists at the Max Planck Institute for Gravitational
Physics (Albert Einstein Institute/AEI)
show for the first time the occurrence of an instability in the interior of neutron
stars that can lead to gigantic magnetic fields, possibly triggering one of the most dramatic
explosions observed in the Universe.
This could be explained by a phenomenon that can be triggered in a differentially rotating plasma in
the presence of magnetic fields: neighbouring 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.
At the same time, the recent study supports the idea that ultra strong magnetic fields can be
the key ingredient in explaining the huge amount of energy released by short gamma-ray bursts.