Gamma-Ray Wipe-Out

A massive blast of radiation from space once almost sterilized the Earth

Gamma-ray bursts: the biggest, most powerful explosions in the Universe since the Big Bang. They are a million trillion times brighter than the Sun. Each day, we detect a burst of gamma radiation coming from a random direction in the sky. Lasting anywhere from a fraction of a second to several minutes, these high-energy astronomical enigmas have a deadly power.

The monitoring of nuclear-weapon tests led researchers to the biggest bangs in the Universe

Until very recently, we really didn’t know very much about them. Gamma-ray bursts were only discovered in the late 1960s, quite by accident. During the Cold War, the US military sent up satellites to detect signs of illegal nuclear testing by the Soviet Union. These Vela satellites were fitted with gamma-ray detectors, since nuclear explosions release copious amounts of this extremely energetic radiation. The American military was surprised that their satellites instead detected great explosions of gamma-ray photons coming from space.

So what are these gamma-ray bursts? How are they formed, and where do they come from? Over the past 15 or so years, satellites and ground-based observations have provided a mass of data that has helped scientists to answer these questions.

Scientists have identified two kinds of gamma-ray burst (GRB): short duration (average 0.3 second) and long duration (average 30 seconds). Experts suspect that these form in totally different ways. Although they are fairly confident they understand the origin of long-duration GRBs, short duration GRBs remain a puzzle.