Astronomers have described the first radiation belt observed outside our solar system, using a coordinated network of 39 radio dishes from Hawaii to Germany to obtain high-resolution images High. Continuous and intense radio emission imaging from an extremely cold dwarf reveals the presence of a cloud of high-energy electrons trapped in the object's strong magnetic field, forming a similar double-lobed structure as radio images of radiation belts from Jupiter.
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Artist's impression of an aurora and the surrounding radiation belt of the ultracool dwarf LSR J1835+3259. Credit: Chuck Carter, Melodie Kao, Heising-Simons Foundation |
"We actually visualized the target's magnetosphere by observing the plasma that emits radio waves - its radiation belt - in the magnetosphere. This has never been done before for something that has about the size of a gas giant outside our solar system." Melodie Kao, a postdoctoral fellow at UC Santa Cruz and first author of a paper on the new findings published May 15 in the journal Nature.
Strong magnetic fields form a "magnetic bubble" around a planet called the magnetosphere, which can trap and accelerate particles to near the speed of light.All the planets in our solar system with such magnetic fields, including Earth, as well as Jupiter and other giant planets, have radiation belts made up of charged particles. This high energy is trapped by the planet's magnetic field.
Earth's radiation belts, known as the Van Allen belts, are large donut-shaped regions of high-energy particles trapped by the solar wind by the magnetic field. Most of the particles in Jupiter's rings come from volcanoes on its moon Io. If you could put them side by side, the radiation belt that Kao and his team imagine would be 10 million times brighter than Jupiter's rings.
Particles deflected by the magnetic field toward the poles produce the aurora ("aurora") as they interact with the atmosphere, and Kao's team also obtained the first image that could tell the difference. between an object's aurora position and its radiation belts outside our solar system.
The extremely cold dwarf imaged in this study lies on the boundary between low-mass stars and high-mass brown dwarfs. “Although the formations of stars and planets may be different, their internal physics may be very similar in this part of the continuum that links low-mass stars with other massive stars. brown dwarfs and gas giants,” explains Kao.
Characterizing the strength and shape of the magnetic field of this type of object is largely uncharted territory, she 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 have no good way to easily test these predictions.
"The aurora can be used to measure the strength of a magnetic field, but not its shape.We designed this experiment to present a method for assessing the shape of magnetic fields on brown dwarfs and possibly exoplanets," said Kao.
The strength and shape of a 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 atmosphere and climate," Kao said.
To generate a magnetic field, the interior of a planet must be hot enough to have conductive liquid, which in the case of Earth is molten iron in its core. In Jupiter, the conductive liquid is hydrogen under such pressure that it becomes metallic. Kao said metallic hydrogen can also generate magnetic fields in brown dwarfs, while the conductive liquid inside stars is ionized hydrogen.
The ultracool dwarf known as LSR J1835+3259 was the only object Kao felt confident would yield the high-quality data needed to resolve its radiation belts.
"Now that we've established that this particular kind of steady-state, low-level radio emission traces radiation belts in the large-scale magnetic fields of these objects, when we see that kind of emission from brown dwarfs—and eventually from gas giant exoplanets—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 said, adding that she is looking forward to when the Next Generation Very Large Array,
currently being planned by the National Radio Astronomy Observatory (NRAO), can image many more extrasolar radiation belts.
"This is a critical 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," said co-author Evgenya Shkolnik at Arizona State University, who has been studying the magnetic fields and habitability of planets for many years.
The team used the High Sensitivity Array, consisting 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 across the world, we can make incredibly 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, D.C.," said co-author Jackie Villadsen of Bucknell University. Amy Mioduszewski at NRAO in research planning and data analysis, as well as Villadsen and Shkolnik multi-wavelength flare expertise.