What Are Gamma-ray Bursts?

The most powerful explosions known in the universe are gamma-ray bursts (GRBs) — brief, intense outbursts of gamma rays, the highest-energy light. They can erupt with a quintillion (a 10 followed by 18 zeros) times the luminosity of our Sun.

Astronomers separate GRBs into two main classes: short, where the initial burst of gamma rays lasts less than two seconds, and long, where it lasts two seconds or more (typically about a minute).

Astronomers associate short bursts with the collision of compact remnants, like a pair of neutron stars or a neutron star and a black hole, where the merger results in a new (or larger) black hole and a short-lived explosion. They link long GRBs to the explosive deaths of very massive stars. When the core of a such a star runs out of nuclear fuel, it collapses, forming a black hole in its center.

In both classes, the newborn black hole fires off narrow beams of particles, called jets, in opposite directions. The jets contain particles accelerated to near the speed of light. Once they drill through the star or merger debris, they emit gamma rays when they encounter surrounding gas and dust.

As the jets expand into space, they sweep up more and more material, gradually slowing and losing energy. This produces afterglows at progressively longer wavelengths, from gamma rays to X-rays, ultraviolet, optical, infrared, and radio light. Much of what we know about GRBs has come through the study of their afterglows, which can be tracked from days to years after the original explosion.