Radiation Belt Identified Outside The Solar System For First Time Ever

Radiation belts—doughnut-shaped areas bounded by magnetic fields where particles are trapped and accelerated and glow in radio light—are present on every planet in our solar system with global magnetic fields. All of this implies that radiation belts should exist everywhere there is a constant, global magnetic field.

But it is difficult to resolve the diffuse light of a radiation belt, making it difficult to detect the modest emission from an extrasolar radiation belt. However, difficult does not equate to impossibly difficult: for the first time, scientists have captured a picture of a radiation belt encircling an extrasolar object.

That object is LSR J1835+3259, an extremely low-mass red dwarf star that is little over Jupiter's diameter, roughly 77 times Jupiter's mass, and is located around 20 light-years distant.

According to astronomer Melodie Kao of the University of California, Santa Cruz, "We are actually imaging the magnetosphere of our target by observing the radio-emitting plasma - its radiation belt - in the magnetosphere." "For something the size of a gas giant planet outside of our Solar System, that has never been done before."

The Van Allen belts on Earth are chock-full of solar wind debris. Radiation belts are present on Saturn, Mercury, Neptune, and Uranus.

Io, Jupiter's volcanic moon, provides the bulk of the massive radiation belts with large gouts of volcanic material. Even Ganymede, the only moon in the Solar System with its own magnetic field, has a radiation belt. Ganymede is a moon orbiting Jupiter.

And although if extrasolar objects had not been discovered by the radiation belts and magnetic fields that contained them, we had observed signs of their existence.

Low-mass stars and brown dwarfs have displayed behavior like the solar system's auroras. When accelerated charged particles are directed down magnetic field lines and fall into a planet's atmosphere where they interact with other particles, auroras—which are visible on many planets—are created.

LSR J1835+3259 was the ideal target to check attentively for radiation belts since it had showed signals of this auroral activity, which indicated the existence of a global magnetic field.

Kao and her colleagues made observations of the star, paying close attention to the area surrounding it where a radiation belt, when viewed from the side, would appear as two radio-emitting lobes. They did this by utilizing a network of 39 radio telescopes located all over the world to essentially build an Earth-sized radio telescope.

Images confirmed the presence of a double-lobed object surrounding the star that was generating radio waves of a fainter frequency than Jupiter's radiation belt. The star's radio lobes are approximately 10 million times more intrinsically brilliant than Jupiter's because of the star's greater distance from Earth.

Additionally, the radiation detected is of a sort that has previously been detected in brown dwarfs and low-mass stars, but it was previously attributed to outbursts in the stellar corona.

These discoveries not only show that stars and other similar objects can have radiation belts, but they also suggest that humans may have already noticed radiation belts in other similar objects without realizing it.

"Now that we've established that this particular steady-state, low-level radio emission traces radiation belts in the large-scale magnetic fields of these objects, we can more confidently say they probably have a big magnetic field, even if our telescope isn't big enough to see the shape of it," Kao says. "When we see that kind of emission from brown dwarfs- and eventually from gas giant exoplanets."

Astronomers anticipate that this finding will aid their hunt for possibly habitable planets as methods and equipment advance. That's because it's believed that for life to thrive, the Earth's magnetic field is necessary. By preventing dangerous solar radiation from reaching the surface, it shields the atmosphere and the weak creatures that live there from damage.

We will be able to identify planets that are similarly shielded if we have the means to detect magnetic fields around other worlds.

Even if that's still a ways off, this discovery puts us on the correct track.

According to astronomer Evgenya Shkolnik of Arizona State University, "this is a crucial first step in finding many more such objects and honing our skills to search for smaller and smaller magnetospheres, eventually enabling us to study those of potentially habitable, Earth-size planets."

The research has been published in Nature.