March 30, 2006

Colliding Neutron Stars Produce Strongest Magnetic Fields Known in the Universe

The first computer simulation to model the collision of two magnetised neutron stars shows that the impact generates the strongest magnetic fields known in the Universe.  The gigantic fields are more than a thousand million million times stronger than the magnetic field of the Earth and are thought to launch the violent gamma-ray burst explosions.

Neutron stars have masses comparable to that of our Sun, but a radius of only 10 km, so they are even denser than atomic nuclei.  Neutron stars that orbit around each other in binary systems will, according to Einstein's Theory of General Relativity, slowly spiral in towards each other. Their final fate is a thunderously violent collision.

The results of simulations of these collisions are being presented at the Royal Astronomical Society's National Astronomy Meeting on 5th April and at the Ringberg-conference on Nuclear Astrophysics on the 7th April. They are published in the online journal Science Express on 30th March.

Dr. Daniel Price from the University of Exeter, UK, said "It is only recently that we have the computing power available to model the collisions and take into account the effects of magnetic fields. It has taken us months of nearly day and night programming to get this project running." 

Prof. Stephan Rosswog from the International University of Bremen, Germany, adds "This is an incredible result. Magnetic fields that we are familiar with, say from a magnet at your refrigerator, have strength of about 100 Gauss. Such a collision produces field that are an incredible 10 million million times stronger."

In the supercomputer simulations, Price and Rosswog show that within the first millisecond of the collision, magnetic fields are produced that are stronger than any other magnetic field that is known in the Universe. 

The calculations are a computational challenge because they include a lot of exotic physics, including effects of high-density nuclear physics, particle physics and General Theory of Relativity. To calculate only a few milliseconds of a single collision takes several weeks on a parallel supercomputer.

It has long been suspected that such a collision may be at the heart of some of the brightest explosions in the Universe since the Big Bang, so-called short gamma-ray bursts. Recent detections of 'afterglows' of such bursts have confirmed this idea, but much of the physics behind these explosions lies still in the dark.


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