Spanish astronomers reveal the first detailed image of a radiation belt outside the solar system

More than half a century ago, in 1958, American physicist James Van Allen discovered that planet Earth was surrounded by ions and electrons trapped in the earth’s magnetic field and disrupting the communication of space probes.

They were observed almost simultaneously radiation belt of this kind, but giants, around the planet Jupiter, due to outbursts detected by radio observations. Now they have been discovered for the first time outside the solar system and described in detail (compared to previous studies), showing the universality of this structure.

Specifically in the Brown dwarf LSR J1835+3259around which a team of scientists from the University of Valencia (UV) discovered last January a radiation belt composed of energetic particles trapped in its intense magnetic field.

The study, which also involves researchers from the Institute of Astrophysics of Andalusia (IAA-CSIC), the Royal Academy of Exact, Physical and Natural Sciences of Spain (RAC) and the Donostia International Physics Center (DIPC), is now published in the magazine Science.

Brown dwarfs, along with very low mass stars, form the astronomical category of ultra cool dwarvesand in the case of LSR J1835, the donut-shaped radiation belt is almost a scaled-down version of the well-known Van Allen belts—named after its discoverer—that occur on our planet and Jupiter.

“Although they differ in size and energy, this similarity becomes clear when you look at the radiation belts of Jupiter and LSRJ1835 side by side,” says the lead author. John Baptist ClimentUV astronomer also associated with the International University of Valencia.

“The diameter of the magnetic structure around this ultracold dwarf is 10 times larger than that of Jupiter and a million times stronger,” he adds. In reality, LSRJ1835 is 60 times heavier than this gas giant and spinning three times as fast. Both factors together generate an intense magnetic field on its surface, which is very similar to the field emitted in a magnetic resonance device.

The magnetic structure around this ultracold dwarf is ten times larger than that of Jupiter and millions of times stronger.

Juan Bautista Climent (UV)

LSRJ1835’s new radiation belt has been observed at radio wavelengths thanks to the European network Very Long Baseline Interferometry (VLBI). LSRJ1835 is a brown dwarf, a transitional body between a star and a planet, located 18 light-years away. Therefore, it is extremely small and only the use of such instruments allows a detailed view of its surroundings.

To map its radiation belt, the European VLBI network combined huge radio antennas spread across the globe, from Spain to China, from Sweden to South Africa.

They all scanned the brown dwarf simultaneously, achieving a resolution 50 times better than that of the James Webb Space Telescope.

very bright auroras

The extraordinary detail of LSRJ1830’s radio image has also revealed other mysteries about the object. The study concludes that the radiation belt, just like on Earth and Jupiter, contributes to the formation of polar lights.

However, the gigantic radiation belt of LSRJ1835 leads to extrasolar auroras of a energy so great this will be more than an affable glow.

“These auroras emit energy in a very concentrated manner and at very high temperatures, producing peaks in radio emission that are 10 times larger than the total emission from LSRJ1835,” says the co-author. Jose Carlos GuiradoProfessor of Astronomy at UV.

“For the first time we have a picture of it Aurora seen in polarized light and is located halfway between the two emission zones that correspond to the belt, near the surface of LSRJ1835,” adds Guirado.

Both the aurora and the radiation belt can be observed simultaneously, providing valuable information about the geometry of this brown dwarf. The study suggests that radio-emitting ultracold dwarfs have dipole-ordered magnetic fields with morphologies and auroras similar to those of gas giants like Jupiter.

Reconstructed radio images of LSR J1835+3259 using European VLBI network and explanatory scheme. The two spots correspond to the annular radiation belt seen from the edge. The contour represents the highly polarized light originating from the aurora near the brown dwarf’s surface, which is midway between the radio components of the radiation belt. / Joan Climent et al./Sci

On the other hand, the results of this study on LSRJ1835 show that the European VLBI network is capable of this Map radiation belts on nearby objectsand to anticipate that future instruments such as square kilometer arraywould extend these studies to smaller and more distant objects, including exoplanets.

Knowing the magnetic environment of exoplanets is extremely important in assessing the possibilities of housing extraterrestrial life. “The possibility of life depends in large part on the properties of the radiation surrounding these new worlds,” recalled another author of the study: Miguel Angel Perez Torresthe IAA CSIC.