IN a recent issue of Nature, astronomers describe the first radiation belt observed outside the earth’s solar system, using a coordinated array of 39 radio dishes from Hawaii to Germany. The images of persistent, intense radio emissions from an ultracool dwarf star revealed the presence of a cloud of high-energy electrons trapped in the object’s powerful magnetic field, forming a double-lobed structure.
Strong magnetic fields form a “magnetic bubble” around a planet called a magnetosphere, which can trap and accelerate particles to near the speed of light. All the planets in the solar system that have such magnetic fields, including the earth and Jupiter, have radiation belts. The earth’s radiation belts, known as the Van Allen belts, are large doughnut-shaped zones of high-energy particles captured from solar winds by the magnetic field. This extrasolar radiation belt would be 10 million times brighter than Jupiter’s.
