Since the signing of the Nuclear Test Ban Treaty in 1963, American scientists have launched satellites with the aim of monitoring the Earth for peaks of gamma rays, the emission of which is the telltale sign of a clandestine nuclear test. However, scientists were surprised when they found gamma-ray bursts not from Earth but from space.
These transient radiation spikes were not the work of extraterrestrials detonating nuclear bombs. They were the signature of a gamma-ray burst, the most powerful and most dangerous explosion in the Universe. These events are so lethal that if they occurred anywhere in Earth’s cosmic vicinity, they would sterilize the planet. To better understand the phenomenon, researchers at the CERN laboratory in Europe are using a powerful particle accelerator to recreate the intense conditions that characterize a gamma-ray burst in the laboratory.
An explosion of sterilizing luminosity
A gamma-ray burst is thought to form when a massive star runs out of nuclear fuel and its core collapses in on itself, forming a black hole. As the star collapses, it forms very strong magnetic fields, which prevent some of the star’s material from falling into the black hole. These magnetic fields drive some of this material towards the star’s poles, then fling it through space at nearly the speed of light.
The stream of material ejected from each pole is called a jet, and the material itself is a hot plasma, which is the result of heating a gas to such extremes that it loses some of the electrons from its atoms. The jets also include gamma rays, along with an intense spray of electrons and positrons (the antimatter equivalent of electrons). Electrons and positrons interact with magnetic fields in complex ways.
These plasma jets are extremely bright. In less than a second they produce as much energy as the Sun will emit in 10 billion years and can be easily detected billions of light-years away. They are also quite lethal. According to some theories, if a gamma-ray burst were to occur within about 200 light-years of Earth and the jets were aimed directly at us, our planet would be vaporized. At greater distances, but still in the Milky Way, the radiation would sterilize all life on the side of the Earth facing the blast.
Even a burst of gamma rays from over a billion light-years away can disrupt radio communications here on Earth. They are so powerful. Fortunately, these outbursts are relatively rare, and astronomers don’t believe any star in Earth’s vicinity is a candidate for generating one. However, some scientists believe that a gamma-ray burst was responsible for the Ordovician-Silurian mass extinction about 440 million years ago, during which about 85% of species at the time went extinct.
A fireball’s chance to solve a mystery
We can describe the basic mechanisms that drive gamma-ray bursts, but the details remain a mystery. It is very difficult for any laboratory to recreate the necessary combination of chaotic magnetic fields within a very hot, dense plasma. However, researchers are finally getting a glimpse into these complicated conditions.
Scientists at the CERN laboratory in Europe have created a structure they call the Fireball. CERN is Europe’s leading particle physics laboratory, most famous for hosting the Large Hadron Collider, the world’s highest-energy particle accelerator. The Collider is the final component in a series of smaller particle accelerators. Each accelerator increases the energy of a particle beam by a certain amount and then passes it on to the next accelerator in the chain. In many ways, it’s like the various gears of an automobile: each gear is set for a certain speed.
One of the accelerators in the Large Hadron Collider complex is called the superproton synchrotron. In this accelerator, protons reach 99.9998% of the speed of light. These protons are then fired at a fixed target. In a multi-step procedure, they are converted into a beam of highly energetic electrons and positrons. Finally, this electron/positron beam is directed towards a container in which a hot plasma is formed. (This isn’t as dangerous as it sounds. After all, fluorescent lamps contain plasma, as do plasma balls, which can be purchased at novelty stores.)
Thus, the Fireball facility is capable of generating a miniature version of the complicated conditions found within the jet of a gamma-ray burst. Electrons and positrons rippling through a plasma is exactly what happens in the jet of a gamma ray burst. Magnetic fields in the plasma disrupt the beam of electrons and positrons, and this disruption gives shape to further magnetic fields, increasing complexity.
However, using this unique equipment, scientists expect to improve our understanding of the most energetic events in the cosmos. When scientists announce their findings, the largest explosions ever observed will become a little less mysterious.
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