The key role of magnetic fields in binary neutron star mergers (Q776790)

On August 17, 2017, a strong burst of gravitational waves was detected, accompanied by a short gamma-ray burst and a visible light observational event coming from the same spatial location. Detailed analysis of all this evidence led to a conclusion that this was a merger of a binary neutron star -- two neutron stars that were originally rotating around each other. To better understand this process, physicists have been running computer simulations; this paper is a survey of different simulation techniques and results of these simulations. Somewhat surprisingly, it turned out the key role in the merger process is played by magnetic fields. It was surprising since the original magnetic fields are not extraordinarily strong -- only about \(10^{10}\) Gauss. However, during the merger, instabilities appear, which -- as typical for dynamical systems -- lead to an exponential growth of magnetic fields to values about \(10^{16}\) Gauss, much stronger than any other magnet in the Universe. The fact that magnetic fields play the key role -- and that the effect of other fields can thus be, in the first approximation, largely ignored -- makes simulations somewhat easier. However, direct simulations are still not possible. The reason for this difficulty is that the same instability that boosts the magnetic fields also leads to strong spatial inhomogeneities, which cannot be properly described even at the current 12-meter-resolution level -- the smallest possible grid size achievable on most powerful high performance computers. The paper overviews indirect techniques that different teams have used to come up with reasonable simulation results, and lists possible physical interpretations of these results.