Astronomers using the Karl G. Jansky Very Large Array have observed long-lasting aurora-like radio bursts above a sunspot. This discovery could help us better understand our own star as well as the behavior of distant stars that produce similar radio emissions.
“This sunspot radio emission represents the first detection of its kind,” said Dr. Sijie Yu, an astronomer at the New Jersey Institute of Technology.
“Detected about 40,000 km (25,000 miles) 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.”
On Earth, and other planets such as Jupiter and Saturn, aurorae 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 aurorae.
The team’s analysis 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 aurorae, 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,” Dr. 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 in addition to the previously proposed aurorae in their polar regions.
“The discovery excites us as it challenges existing notions of solar radio phenomena and opens new avenues for exploring…
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