The explosive birth of black holes

This animated artistic impression illustrates the immense release of energy during a gamma-ray burst (GRB). The hugely energetic explosions of GRBs take place in distant galaxies and are among the most powerful and luminous events observed since the Big Bang.  

The energy is released in the initial phase of a supernova explosion of a star, in an extremely short time with respect to the eons of a star’s lifetime. Typical GRB events last from a few milliseconds to a few hours and the outflow is dominated by the most energetic type of light, gamma rays – hence the name. In that short moment, the energy released by the burst outshines by several times the total amount of energy emitted by all the stars in a the galaxy (over that period). 

Most of the GRBs (70%) last longer than two seconds and are classified as long gamma-ray bursts. Astronomers think these catastrophic releases of energy are associated with the births of new black holes. The black holes are formed within the heart of the largest stars – stars more than 20 times more massive than the Sun – in the last moments of their life.   

Throughout its life as shining source of light, a star maintains its shape by the processes of nuclear fusion taking place in its interior. Nuclear fusion of lighter elements (typically hydrogen) into heavier ones (for example helium) is driven by the enormous inward gravitational pressure within the star. In a game of push-and-pull, the energy released by nuclear reactions generates enough outward pressure to balance out the contracting force of gravity. When the nuclear fuel in a star’s core eventually dries up, there is no longer enough outward pressure to counteract the crushing force of gravity and a very massive star rapidly collapses to form a black hole.   

This process is extremely violent and sudden. As shown in the clip, the black hole drives powerful jets of particles traveling near the speed of light. The jets pierce through the outer layers of the disintegrating star, emitting X-rays and gamma rays as they stream into space.