Unprecedented Discovery: Astronomers Find First Radiation Belt Beyond Our Solar System

For the first time, astronomers have detected a radiation belt outside our solar system, around a brown dwarf named LSR J1835+3259. This ring is 10 million times stronger than Jupiter’s belt and represents an important step in the discovery of potentially habitable Earth-sized planets. The discovery was made possible thanks to a worldwide network of 39 radio discs.

Radiation belts are donut-shaped magnetic structures enveloping a planet filled with very high-energy charged electrons and particles.

Originally discovered around Earth in 1958 with the Explorer 1 and 3 satellites, radiation belts are now known to be a common feature of the Solar System:
All planets with large-scale magnetic fields – including Earth, Jupiter, Saturn, Uranus, and Neptune – have them. However, so far no radiation belts have been clearly observed outside our solar system.

A small team of astronomers is led by Melodie Kao, formerly of Arizona State University and now a 51 Pegasi b Fellow at the University of California, Santa Cruz, and includes Professor Evgenya Shkolnik of the School of Exploration Earth and the space station, discovered the first radiation. outer ring of our solar system. The results were published May 15 in the journal Nature.

The discovery was made around the “brown dwarf” LSR J1835+3259, which is about the size of Jupiter but much denser. Located just 20 light-years from the constellation Lyra, it is not massive enough to be a star, but too massive to be a planet. Because radiation belts have never been clearly seen outside our solar system, it’s unclear if they could exist around objects other than planets.

“This is a necessary first step in finding more such objects, and honing our skills in finding increasingly smaller magnetospheres, ultimately allowing us to see more of such objects,” said Shkolnik, who worked on the study. we study potentially habitable planets the size of this planet.” magnetic. environment and habitability of exoplanets for many years.

Although invisible to the human eye, the radiation belt this team discovered is a giant structure. Its outer diameter spans at least 18 Jupiter diameters, and the brightest inner regions are separated by 9 Jupiter diameters. Made up of particles traveling at close to the speed of light and illuminating at radio wavelengths, this newly discovered extrasolar radiation belt is nearly 10 million times stronger than Jupiter’s, itself is millions of times brighter than Earth and has the most energetic particles of any solar energy. system planet. The team captured three high-resolution images of radio-emitting electrons trapped in the magnetosphere of LSR J1835+3259 over the course of a year using a now well-known observation technique to photograph a black hole in our galaxy.

For the first time, astronomers have detected a radiation belt outside our solar system, around a brown dwarf named LSR J1835+3259. This ring is 10 million times stronger than Jupiter’s belt and represents an important step in the discovery of potentially habitable Earth-sized planets. The discovery was made possible thanks to a worldwide network of 39 radio discs. Radiation belts are donut-shaped magnetic structures enveloping a planet filled with very high-energy charged electrons and particles.  

By combining 39 satellite dishes spanning from Hawaii to Germany to create an Earth-sized telescope, the team solved the brown dwarf’s dynamic magnetic environment, known as the “magnetic stratosphere,” for the first time. first observed in the outer solar system. They were even able to see the shape of this magnetic field clearly enough to deduce that it could be a dipole magnetic field like those of Earth and Jupiter.

“By combining satellite dishes from around the world, we are able to create extremely high-resolution images to see things no one has ever seen before. Our images are comparable. with the top row reading of the eye chart in California when held in Washington, DC,” said co-author Professor Jackie Villadsen of Bucknell University.

However, Kao and his team have the first clues that they will find a radiation belt around this brown dwarf. By the time the team made these observations in 2021, radio astronomers had observed that LSR J1835+3259 was emitting two types of detectable radio emissions. Kao herself was part of a group that confirmed six years ago that her periodically flashing beacon-like radio emissions were radio-frequency auroras.

But LSR J1835+3259 also has more stable and weaker radio emission. The data suggest that these weaker emissions cannot come from stellar light trails and are, in fact, very similar to Jupiter’s radiation belts.

The team’s findings suggest that such a phenomenon may be more universal than initially thought – occurring not only on planets but also on brown dwarfs, low-mass stars and possibly even massive stars. very large amount. The region around a planet’s magnetic field – the magnetosphere – including Earth, can protect the planet’s atmosphere and surfaces from damage by cosmic particles and high-energy solar energy .

“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. .

In addition to the observed radiation belt, their study revealed a difference in the “shape” and spatial position of the aurora (similar to Earth’s aurora) compared to an object’s radiation belt. bodies outside our solar system.

“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. “An analogy is that the radiation belts are like the ‘meters’ of the planets living in the vicinity of our solar system, except instead of flowers we have luminous energetic particles at the different wavelengths and luminosity.

“The specific properties of each radiation belt tell us about the energy, magnetic and particle sources of this planet:
how fast it spins, how strong its magnetic field is, how far away it lives from the sun, will it have moons that can provide more particles or rings like Saturn that will absorb them , etc. For the first time, we can see brown dwarfs and low-mass stars. I look forward to the day when we can learn more about the magnetospheres inhabited by exoplanets. 

Reference: “Resolved imaging confirms a radiation belt around an ultracool dwarf” by Melodie M. Kao, Amy J. Mioduszewski, Jackie Villadsen and Evgenya L. Shkolnik, 15 May 2023, Nature.
DOI: 10.1038/s41586-023-06138-w

This work is supported by NASA and the Heising-Simons Foundation.

The team was led by Melodie Kao, formerly a NASA Hubble Postdoctoral Fellow at ASU, and currently a Heising-Simons 51 Pegasi b Fellow at UC Santa Cruz, and consists of Amy Mioduszewski, associate scientist at the National Radio Astronomy Observatory, Professor Jackie Villadsen at Bucknell University and Professor Evgenya Shkolnik at ASU. They used the Karl G. Jansky Very Large Array, the Very Long Baseline Array, and the Robert C. Byrd Greenbank Telescope managed by the National Radio Astronomy Observatory (NRAO) in the United States and the Effelsberg radio telescope operated by the Max Planck Institute for Radio Astronomy in Germany for the High Sensitivity Array.