First radiation belt observed outside the solar system

May 15. (EUROPE PRESS) –

Astronomers have described the first radiation belt observed outside our solar system, using a coordinated array of 39 radio antennas from Hawaii to Germany to obtain high-resolution images.

Images of persistent and intense radio emissions from an ultracool dwarf reveal the presence of a cloud of high-energy electrons trapped in the object’s powerful magnetic field, forming a double-lobe structure analogous to radio images of Jupiter’s radiation belts.

“We’re actually taking pictures of our target’s magnetosphere by looking at the radio-emitting plasma, its radiation belt, in the magnetosphere. That has never been done before for something 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 May 15 in Nature.

Strong magnetic fields form a “magnetic bubble” around a planet called the magnetosphere, that can trap and accelerate particles to almost the speed of light. All of the planets in our solar system that have such magnetic fields, including Earth, as well as Jupiter and the other giant planets, have radiation belts consisting of these high-energy charged particles trapped by the planet’s magnetic field.

Earth’s radiation belts, known as the Van Allen belts, are large doughnut-shaped zones of high-energy particles captured from the solar winds by the magnetic field. Most of the particles in Jupiter’s belts come from volcanoes on its moon Io. If I could put them next to each other, the radiation belt that Kao and his team have imaged would be 10 million times brighter than Jupiter’s.

Particles deflected poleward by the magnetic field generate auroras (“northern lights”) when they interact with the atmosphere, and Kao’s team also obtained the first image capable of distinguishing the location of an object’s aurora and its belts. radiation outside our solar system.

The ultracool dwarf imaged in this study straddles the boundary between low-mass stars and massive brown dwarfs. “While the formation of stars and planets may be different, the physics within them may be very similar in that 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 fields of this class of objects is largely uncharted territory, 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 haven’t had a good way to easily test those predictions.

“Auroras can be used to measure the strength of the magnetic field, but not the shape. We designed this experiment to show a method for evaluating the shapes of magnetic fields in brown dwarfs and eventually exoplanets,” Kao said. it’s a statement.

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

To generate a magnetic field, a planet’s interior must be hot enough to contain electrically conductive fluids, which in Earth’s case is molten iron at its core. On Jupiter, the conductive fluid is hydrogen under so much pressure that it turns metallic. Metallic hydrogen probably also generates magnetic fields in brown dwarfs, Kao said, while inside stars the conductive fluid is ionized hydrogen.

The ultracool dwarf known as LSR J1835+3259 was the only object Kao was confident would provide the high-quality data needed to resolve its radiation belts.

“Now that we have established that this particular type of low-level, steady-state radio emission traces radiation belts in the large-scale magnetic fields of these objects, when we see that type of emission from brown dwarfs, and eventually from gas giant exoplanets : we can say with more confidence that they probably have a large magnetic fieldeven if our telescope is not big enough to see its shape”Kao said, adding that he is looking forward to when the Next Generation Very Large Array, which is currently being planned by the National Radio Astronomy Observatory (NRAO), is able to image many more extrasolar radiation belts.

“This is a critical first step in finding many more such objects and honing our skills in searching for smaller and smaller magnetospheres. which will ultimately allow us to study those of potentially habitable Earth-sized planets,” said co-author Evgenya Shkolnik at Arizona State University, who has been studying magnetic fields and the habitability of planets for many years.

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