The first radiation belt outside the solar system has been observed

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Astronomers for the first time noticed a band of radiation around an object outside our solar system.

Belt of energetic electrons surrounds a Jupiter-sized body about 18 light-years from Earth astronomers reported on May 15 in Nature . When electrons move, they emit radio waves. Such radiation belts make it possible to understand the shape of the magnetic field of a space object, its internal structure and, possibly, even the presence of satellites.

In our solar system, every planet with a global magnetic field has radiation belts. Earth has Van Allen belts, rings of electrons captured by the Sun. Jupiter’s radiation belts receive most of their particles from the volcanic moon Io. In these cases, the planet’s magnetic field traps electrons in a bubble around the planet, like fireflies in a jar.

To find similar belts outside the Solar System, astronomer Melody Kao and colleagues observed a Jupiter-sized object called LSR J1835+3259 with a network of 39 radio dishes stretching from Hawaii to Germany. Together, the dishes effectively created a radio telescope about the width of Earth, allowing the team to focus on the object’s surroundings.

The team spotted a belt that is very similar to Jupiter’s belt, but 10 million times brighter, says Kao of the University of California, Santa Cruz. The object is nearly 80 times more massive than Jupiter, making it either a miniature star or a massive brown dwarf, a dim star-like body not powerful enough to support hydrogen fusion.

One big mystery is where the electrons come from. The object does not orbit the star and does not appear to emit flares. Kao says a volcanic satellite would qualify, but that’s still speculation.

Knowing that LSR J1835+3259 has a radiation belt will help researchers interpret data from exoplanets in the future, even if astronomers can’t see such belts directly.

“Exoplanet magnetism is really in its infancy,” says Kao. “Until we can characterize the magnetic fields of exoplanets, we will miss entire segments of their life histories.”

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