Neutron stars merging, gamma_ray burst. Animation clip 4 of 11 showing two neutron stars producing a gamma_ray burst GRB as they merge to form a black hole. GRBs are extremely energetic releases of gamma rays, visible across the universe in the direction the radiation is emitted. The precise cause varies depending on the duration. Longer ones are thought to occur during the death and collapse of massive rapidly rotating stars. Shorter ones as here are thought to occur during the merger of colliding neutron stars as they form a black hole. Neutron stars are immensely dense stellar core remnants, formed after a massive star runs out of hydrogen fuel and its core collapses. Due to the immense masses involved, large amounts of energy are released when two neutron stars merge. Later clips in this sequence K003/2670_2660 show the process of neutron star merger in detail, as modelled by the Damiana supercomputer at Germany磗 Max Planck Institute for Gravitational Physics.