Gamma-ray bursts (GRBs) are the biggest explosions in the cosmos emitting large amounts of the most energetic form of light, gamma rays. GRBs shine hundreds of times brighter than a typical supernova (the explosive death of a massive star) and are about a million trillion times brighter than the Sun; yet they are short-lived, lasting from a few milliseconds to several minutes. In a few seconds, GRBs can emit more energy than the Sun over its entire 10-billion-year life.

GRBs puzzled astronomers for decades. It wasn’t until Hubble began observing the visible source of these events, that astronomers began to better understand their origins.

GRBs come in two forms, long and short. The initial flash of long GRBs can last two seconds to hundreds of seconds long, while the initial flash of short GRBs lasts less than two seconds. Short GRBs are associated with the collision of two compact objects like two neutron stars or a neutron star and a black hole. They collide to form a kilonova and have a spectrum dominated by more energetic ("harder") gamma rays. Long GRBs stem from the explosive, supernova deaths of massive stars at least 10 times the mass of our Sun and have a spectrum dominated by relatively less energetic ("softer") gamma rays.

Kilonovae also have a unique light signature: they are much brighter in near-infrared light compared to their brightness in visible light. This difference is the result of the heavy elements produced and ejected during the explosion. Elements like gold, platinum, and uranium in the debris cloud scatter shorter wavelengths of visible light, effectively blocking it, while the longer wavelengths of infrared light pass through unimpeded. This characteristic makes Hubble one of the best ways to observe the aftermath of these massive explosions.

Hubble not only sees both near-infrared light and visible light (along with ultraviolet light), it also orbits Earth high above the oxygen and carbon dioxide in our atmosphere that absorbs infrared light. Hubble observations allow astronomers to compare the light curve of GRBs at both visible and near-infrared wavelengths, which helps determine their origins.

Infographic on long and short gamma-ray bursts

NASA and A. Feild (STScI)

A field filled with stars and galaxies against a black background. A small pinkish circle at image center denotes the host galaxy of a gamma-ray burst.

The Hubble Space Telescope’s Wide Field Camera 3 revealed the infrared afterglow (circled) of GRB 221009A and its host galaxy, seen nearly edge-on as a sliver of light extending beyond the burst.

NASA/ESA/CSA/A. Levan (Radboud University); Image Processing: Gladys Kober (NASA/Catholic University of America)

kilonova associated with GW170817 (box) was observed by NASA's Hubble Space Telescope and Chandra X-ray Observatory

The kilonova associated with GW170817 (box) was observed by NASA's Hubble and Chandra X-ray Observatory. Hubble detected optical and infrared light from the hot expanding debris. The merging neutron stars produced gravitational waves and launched jets that produced a gamma-ray burst. Nine days later, Chandra detected the X-ray afterglow emitted by the jet directed toward Earth after it had spread into our line of sight.

NASA/CXC/E. Troja

In this stylized GIF, two neutron stars orbit each other, getting closer and closer until they collide against a blue background. The stars are depicted as nested circles of bluish-white. As they get close, blue clouds of debris are pulled off of each one. After they collide, a black hole forms in the center, surrounded by a horizontal oval cloud of blue debris. An orange cloud of debris shoots up from above and below the black hole. Pink cones of light extend above and below the black hole, extending beyond the orange clouds.

Astronomers suspect that most short-duration gamma-ray bursts, as shown in this animation, originate from merging systems containing neutron stars, objects more massive than the Sun but as small as a city.

NASA’s Goddard Space Flight Center

A massive star, represented by concentric circles of blue with a wavy edge, sits against a blue background. Then the circles start to move inward until a black circle representing a black hole appears. Then plumes of white material move outward from the black hole through the star. Once they reach space, the white plumes turn magenta. They continue to move further and further from the star, which then begins to expand in an explosion that fills the frame with white.

When a massive star runs out of fuel, its core suddenly collapses and forms a black hole, as illustrated here. In some cases, matter swirling into the black hole produces two powerful jets that rush outward at almost the speed of light that cause a gamma-ray burst.

NASA’s Goddard Space Flight Center