Scientists have detected persistent radio flares from the Sun, similar to the aurora borealis on Earth, opening new ways to study solar and stellar phenomena. A team of NASA-funded scientists has discovered long-duration radio signals emitted from the Sun, similar to those associated with the aurora borealis (northern and southern lights) on Earth.

Detected about 25,000 miles (40,000 km) above the sunspot, a relatively cool, dark and magnetically active region of the Sun, such radio bursts had previously been seen only on planets and other stars.

“This is the first detection of this type of sunspot radio emission,” said Xiji Yu of the New Jersey Institute of Technology in Newark, lead author of a paper reporting the discovery in the January 2024 issue of Nature Astronomy. The study was first published online in November 2023.

This discovery could help us better understand the behavior of our own star as well as distant stars that produce similar radio emissions.

Ideas about solar and star events

The Sun often emits short radio bursts lasting minutes or hours. But the radio bursts, detected by Yu’s team using Carl G. Jansky’s very large antenna array in New Mexico, continued for more than a week.

These sunspot radio bursts also have other properties, such as their spectra (or intensities at different wavelengths) and polarization (the angle or direction of the radio waves), that are much more similar to the radio emissions produced in Earth’s polar regions. and other aurora planets.

On Earth (and other planets such as Jupiter and Saturn), auroras flicker in the night sky when solar particles are captured by the planet’s magnetic field and pulled toward the poles, where magnetic field lines meet. Particles accelerating towards the poles produce intense radio radiation at frequencies around a few hundred kilohertz, which then hit atoms in the atmosphere, causing them to emit light in the form of an aurora.

Yu’s team’s analysis suggests that radio flares above the sunspot probably form in a similar way, that is, when energetic electrons are captured and accelerated by the sunspot’s converging magnetic fields. Unlike auroras on Earth, radio bursts from sunspots occur at much higher frequencies, from hundreds of thousands of kilohertz to about 1 million kilohertz. “This is a direct result of the sunspot’s magnetic field being thousands of times stronger than Earth’s,” Yu said.

Expanding the understanding of stellar activity

Similar radio emissions have previously been observed from some types of low-mass stars. The discovery opens up the possibility that aurora-like radio emission may come from large spots on these stars (called “starspots”), in addition to previously suggested auroras in the polar regions.

“This discovery is exciting for us because it challenges current understandings of solar radio phenomena and opens new ways to study magnetic activity in both our Sun and distant star systems,” Yu said.

“NASA’s growing heliophysics fleet is well-suited to continue searching for the sources of these radio flares,” said Natchimutuk Gopalswamy, a heliophysicist and solar radio researcher at NASA’s Goddard Space Flight Center. “For example, the Solar Dynamics Observatory constantly monitors active regions of the Sun that are likely to cause this event.”

Meanwhile, Yu’s team plans to look at other solar radio bursts to see if they are aurora-like radio bursts like the ones they found. “We are trying to determine whether some of the previously reported solar flares are these newly identified emission cases,” Yu said. To learn more about this research, check out the mysterious aurora-like radio emission detected above the sunspot.