Binary Neutron Star Simulations


Neutron stars form when a star of greater than 8 times the mass of the Sun runs out of nuclear “fuel” to fuse to heavy elements at its core. When this happens its core succumbs to gravity and its core collapses to a neutron star which is as dense or denser than the matter that makes up an atomic nucleus and concentrates 1.4 times the mass of the sun within 10 km. If two stars that form a binary both become neutron stars, a neutron star binary is born that forms one of the targets for LIGO. Over the course of millions of years this binary system loses energy to gravitational radiation and the two stars spiral towards each other until the finally merge in a cataclysmic collision.

We use numerical relativity and the Einstein Toolkit to simulate the last few hundred milliseconds in the lifetime of neutron star binaries. At this point the stars move with a fraction of the speed of light orbiting each other dozens of times per second and emitting copious amounts of gravitational radiation. We use these simulations to construct models for the emitted radiation that are used by LIGO scientists to look for signals of merging neutron stars in LIGO’s data stream. Shortly before the collide tidal forces tear apart the neutron stars and fling material away from the them, which forms and accretion disk around the black hole or hyerpmassive neutron star that forms in the collision. As the material from the disk falls onto the central object it fuels high energy electromagnetic emission which are expected to be the origin of short hard Gamma ray burst observed with satellites on Earth.