Neutron Star Collisions

Neutron stars, the final state of those heavy stars that do not form black holes, are composed of neutrons at densities of an atomic nucleus. Neutron stars collide with each other relatively frequently throughout the Universe, and recently, physicist Masaru Shibata at the University of Tokyo has formulated a method to learn about the neutron star merger process by looking at the gravitational waves emitted at the time of the merger. When two neutron stars begin to orbit each other, they gradually lose energy by emitting gravitational waves, allowing them to move into closer orbit and eventually merge. The final outcome of the merged material depends on the mass of the initial neutron stars: at a certain threshold mass, the two neutron stars merge to form a black hole, however, below this threshold, they merely form a large neutron star. The value of the threshold mass is still unknown, as different models of the properties of the neutron star material produce different threshold masses. In his study, Shibata found that if a neutron star merger occurred within 150 million lightyears from Earth, the gravitational waves emitted in the merger would be detectable by LIGO (Laser Interferometer Gravitational Wave Observatory). Furthermore, the exact characteristics of the signal detected by LIGO could then be interpreted to find the threshold mass above which the merger forms a black hole. More on his research here, and be sure to check out the simulations at the bottom (.mpg files).