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Simulation offers insight into short gamma-ray bursts

A new supercomputer simulation has shown that the collision of two neutron stars can produce the magnetic structures thought to power the high-speed particle jets associated with short gamma-ray bursts (GRBs). The study provides the most detailed glimpse of the forces driving some of the universe's most energetic explosions.

The state-of-the-art simulation ran for nearly seven weeks on the Damiana computer cluster at the Albert Einstein Institute (AEI) in Potsdam, Germany. It traces events that unfold over 35 milliseconds – roughly three times faster than the blink of an eye. GRBs are among the brightest events known, emitting as much energy in a few seconds as our entire galaxy does in a year. Most of this emission comes in the form of gamma rays, the highest-energy form of light.

‘For the first time, we've managed to run the simulation well past the merger and the formation of the black hole, said Chryssa Kouveliotou, a co-author of the study at NASA's Marshall Space Flight Center in Huntsville, USA. ‘This is by far the longest simulation of this process, and only on sufficiently long timescales does the magnetic field grow and reorganise itself from a chaotic structure into something resembling a jet.’

The authors note the ultimate proof of the merger model will have to await the detection of gravitational waves – ripples in the fabric of space-time predicted by relativity. Merging neutron stars are expected to be prominent sources, so the researchers also computed what the model's gravitational-wave signal would look like. Observatories around the world are searching for gravitational waves, so far without success because the signals are so faint.

The study is available online and will appear in the 1 May edition of The Astrophysical Journal Letters.

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