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NASA-Supported Team Discovers Aurora-Like Radio Bursts Above Sunspot
A NASA-funded team of scientists has discovered long-lasting radio signals emanating from the Sun that are similar to those associated with auroras – northern and southern lights – on Earth.
Scientists have discovered radio bursts above a sunspot that resemble radio emissions from auroras on Earth. The pink-purple streaks in this illustration represent the radio emissions, with higher-frequency radio signals in pink, closer to the sunspot, and lower frequencies in purple. The thin lines represent magnetic field lines above the sunspot. The sunspot is the dark region on the Sun at the bottom. Photo: Sijie Yu, New Jersey Institute of Technology
Detected about 25,000 miles (40,000 km) above a sunspot – a relatively cool, dark, and magnetically active region on the Sun – such radio bursts had previously been observed only on planets and other stars.
“This sunspot radio emission represents the first detection of its kind,” said Sijie Yu of the New Jersey Institute of Technology, Newark, who is the lead author of a paper reporting the discovery in the January 2024 issue of Nature Astronomy. The research was first published online in November 2023.
Detected about 25,000 miles (40,000 km) above a sunspot – a relatively cool, dark, and magnetically active region on the Sun – such radio bursts had previously been observed only on planets and other stars.
“This sunspot radio emission represents the first detection of its kind,” said Sijie Yu of the New Jersey Institute of Technology, Newark, who is the lead author of a paper reporting the discovery in the January 2024 issue of Nature Astronomy. The research was first published online in November 2023.
he discovery could help us better understand our own star as well as the behavior of distant stars that produce similar radio emissions.
The Sun often emits short radio bursts that last for minutes or hours. But the radio bursts Yu’s team detected, using the Karl G. Jansky Very Large Array in New Mexico, persisted for over a week.
These sunspot radio bursts also have other characteristics – such as their spectra (or intensity at different wavelengths) and their polarization (the angle or direction of the radio waves) – that are much more like radio emissions produced in the polar regions of Earth and other planets with auroras.
On Earth (and other planets such as Jupiter and Saturn), auroras shimmer in the night sky when solar particles are caught up in the planet’s magnetic field and get pulled toward the poles, where magnetic field lines converge.
As they accelerate poleward, the particles generate intense radio emissions at frequencies around a few hundred kilohertz and then smash into atoms in the atmosphere, causing them to emit light as auroras.
The analysis by Yu’s team suggests the radio bursts above the sunspot are likely produced in a comparable way – when energetic electrons get trapped and accelerated by converging magnetic fields above a sunspot.
Unlike Earth’s auroras, though, the radio bursts from sunspots occur at much higher frequencies – hundreds of thousands of kilohertz to roughly 1 million kilohertz.
“That’s a direct result of the sunspot's magnetic field being thousands of times stronger than Earth’s,” Yu said.
Similar radio emissions have previously been observed from some types of low-mass stars as well. This discovery introduces the possibility that aurora-like radio emissions may originate from large spots on those stars (called “starspots”) in addition to the previously proposed auroras in their polar regions.
“The discovery excites us as it challenges existing notions of solar radio phenomena and opens new avenues for exploring magnetic activities both in our Sun and in distant stellar systems,” Yu said.
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