Astronomers observe the first visible radiation belts outside our solar system

May 15, 2023

(Nanowerk News) Astronomers have described the first observed radiation belts outside our solar system, using coordinated arrays of 39 radio dishes from Hawaii to Germany to obtain high-resolution images. Images of continuous intense radio emission from an ultracool dwarf reveal a cloud of high-energy electrons trapped in the object’s strong magnetic field, forming a double-lobed structure similar to radio images of Jupiter’s radiation belts.

“We actually image our target’s magnetosphere by observing the radio-emitting plasma—its radiation belts—in the magnetosphere. That has never been done before for the size of a gas giant planet outside our solar system,” said Melodie Kao, a postdoctoral fellow at UC Santa Cruz and first author of a paper on the new findings published in Natural (“Completed imaging confirms presence of radiation belts around ultracool dwarf”). Artist’s impression of the auroras and radiation belts around the ultracool dwarf LSR J1835+3259. (Image: Chuck Carter, Melodie Kao, Heising-Simons Foundation)

The strong magnetic field forms a “magnetic bubble” around the planet called the magnetosphere, which can trap and accelerate particles to near the speed of light. All planets in our solar system that have such a magnetic field, including Earth, as well as Jupiter and the other giant planets, have radiation belts made up of high-energy charged particles trapped by the planet’s magnetic field.

Earth’s radiation belts, known as the Van Allen belts, are large donut-shaped zones of high-energy particles captured from the solar wind by the magnetic field. Most of the particles in Jupiter’s belt originate from volcanoes on its moon Io. If you could put them side by side, the radiation belts imaged by Kao and his team would be 10 million times brighter than Jupiter’s.

Particles deflected by a magnetic field toward the poles produce auroras (“northern lights”) when interacting with the atmosphere, and Kao’s team also obtained the first images capable of distinguishing between the location of an object’s aurora and its radiation belts outside our solar system. .

The ultracool dwarfs imaged in this study cross the boundary between low-mass stars and massive brown dwarfs. “Although the formation of stars and planets can differ, the physics within them can be very similar in the soft part of the mass continuum that connects low-mass stars to brown dwarfs and gas giant planets,” Kao explained.

Characterizing the strength and shape of the magnetic field of this class of objects is largely uncharted field, he said. Using their theoretical understanding of these systems and numerical models, planetary scientists can predict the strength and shape of a planet’s magnetic field, but they don’t yet have a good way to easily test those predictions. The extrasolar radiation belt The first image of the extrasolar radiation belt was obtained by combining 39 radio telescopes to form a virtual telescope spanning the globe from Hawaii to Germany. (Image: Melodie Kao, Amy Mioduszewski)

“Aurora can be used to measure the strength of the magnetic field, but not the shape. We designed this experiment to present a method of assessing the shape of the magnetic field in brown dwarfs and eventually exoplanets,” said Kao.

The strength and shape of the magnetic field can be important factors in determining a planet’s habitability. “When we think about the habitability of exoplanets, the role of their magnetic field in maintaining a stable environment is something to consider besides things like atmosphere and climate,” said Kao.

In order to generate a magnetic field, the planet’s interior must be hot enough to have a liquid conducting electricity, which in Earth’s case is liquid iron at its core. On Jupiter, the conducting liquid is hydrogen under so much pressure that it becomes metal. Metallic hydrogen might also generate magnetic fields in brown dwarfs, Kao said, while in the interior of stars, the conducting fluid is ionized hydrogen.

The ultracold dwarf known as LSR J1835+3259 is the only object Kao says is confident of producing the high-quality data needed to resolve its radiation belts.

“Now we have established that this type of well-established low-level radio emission traces radiation belts in the large-scale magnetic fields of these objects, when we look at this type of emission from brown dwarfs—and eventually from gas. giant exoplanets—we can more confidently say they may have large magnetic fields, even if our telescopes aren’t big enough to see their shape,” said Kao, adding that he’s looking forward to the Next Generation Very Large Array, currently being planned by National The Radio Astronomy Observatory (NRAO), can image more of the extrasolar radiation belts.

“This is an important first step in finding more similar objects and honing our skills for searching for increasingly smaller magnetospheres, which will eventually allow us to study potentially habitable Earth-size planets,” said co-author Evgenya Shkolnik at Arizona State University. , who has studied magnetic fields and planetary habitability for many years.

The team used the High Sensitivity Array, which consists of 39 radio dishes coordinated by the NRAO in the United States and the Effelsberg radio telescope operated by the Max Planck Institute for Radio Astronomy in Germany.

“By combining radio dishes from around the world, we can create very high-resolution images to see things no one has ever seen before. Our images are comparable to reading the top row of an eye chart in California while standing in Washington, DC,” said co-author Jackie Villadsen at Bucknell University.

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