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Binary Neutron Stars: Inspiral and Merger

Binary Neutron Star Merger (with magnetic fields)

This movie shows the final stages of the coalescence and the merging of two neutron stars. Neutron stars are dense objects created in certain supernova explosions, and concentrate around 1.5 solar masses inside a radius less than 20 km. Further, they can have extreme magnetic fields. The merging of two neutron stars is believed to be the source of the frequently observed so-called short gamma ray bursts, and is also the most likely source for the creation of heavy elements in the universe, such as gold.

In the movie, the white solid surfaces depict the surfaces of the two neutron stars and the merged object. The latter collapses to a black hole after a while, shown in yellow for better visibility. Afterwards, various amplification effects create strong magnetic fields near the black hole, shown as transparent colors. The magnetic field likely plays a key role in the gamma-ray emission, but the exact mechanism is still a field of active research, in particular with the help of computer simulations such as the one this movie is based on.

This movie is based on the simulations described in T. Kawamura, B. Giacomazzo, W. Kastaun, R. Ciolfi, A. Endrizzi, L. Baiotti, and R. Perna, “Binary neutron star mergers and short gamma-ray bursts: Effects of magnetic field orientation, equation of state, and mass ratio”, Phys. Rev. D 94, 064012 (2016)

Acknowledgements:
These results were obtained with the help of the following grants: PRACE grant GRSimStar (PI Giacomazzo), MIUR FIR grant No. RBFR13QJYF (PI Giacomazzo)

Credit:
Visualisation: W. Kastaun (University of Trento and Max Planck Institute for Gravitational Physics)
Numerical relativity simulation: T. Kawamura, B. Giacomazzo, W. Kastaun, R. Ciolfi, and A. Endrizzi (University of Trento)

Binary Neutron Star Merger (with magnetic fields)

This plot shows the structure of the magnetic field 35 ms after the merger of two magnetized neutron stars (NS) and around 27 ms after the hypermassive merger remnant collapsed to a black hole (BH). One can see that an ordered structure has emerged, with a toroidal field in the debris disk surrounding the BH (shown as blue surface and cut open). More importantly, there is a twister-like field around the BH axis, with field strength above 1013 Gauss. Inside we find a funnel of low mass density (yellow). This is one of the proposed scenarios that might eventually lead to the formation of a short gamma ray burst, although there was no outflow on the short timescale of this simulation. The initial BNS model consists of two 1.51 solar mass NSs with dipolar magnetic fields around 1012 Gauss, following a simplified gamma-law equation of state. Zoom Image
This plot shows the structure of the magnetic field 35 ms after the merger of two magnetized neutron stars (NS) and around 27 ms after the hypermassive merger remnant collapsed to a black hole (BH). One can see that an ordered structure has emerged, with a toroidal field in the debris disk surrounding the BH (shown as blue surface and cut open). More importantly, there is a twister-like field around the BH axis, with field strength above 1013 Gauss. Inside we find a funnel of low mass density (yellow). This is one of the proposed scenarios that might eventually lead to the formation of a short gamma ray burst, although there was no outflow on the short timescale of this simulation. The initial BNS model consists of two 1.51 solar mass NSs with dipolar magnetic fields around 1012 Gauss, following a simplified gamma-law equation of state. [less]
 
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