NJIT Scientists Discover Aurora-Like Radio Emission Over Sunspot

In a study published in Nature Astronomy, astronomers from the New Jersey Institute of Technology’s Center for Solar-Terrestrial Research (NJIT-CSTR) have made detailed radio observations of an extraordinary aurora-like phenomenon – occurring 40,000 km above a relatively dark and cold spot on the planet appears. Sun, also called sunspot.

Researchers say the new radio emission shares characteristics with the auroral radio emissions commonly observed in planetary magnetospheres such as those around Earth, Jupiter and Saturn, as well as in certain low-mass stars.

The discovery provides new insights into the origins of such intense solar radio bursts and may open new avenues for understanding similar phenomena in distant stars with large starspots, said Sijie Yu, lead author of the study and NJIT-CSTR scientist .

“We detected a strange kind of long-lasting polarized radio bursts originating from a sunspot that last for more than a week,” Yu says. “This is very different from the typical transient solar radio bursts that typically last minutes or hours. It is an exciting discovery that has the potential to change our understanding of stellar magnetic processes.”

Famous aurora shows visible in the skies of Earth’s polar regions, such as the Aurora Borealis or Aurora Australis, occur when solar activities disrupt Earth’s magnetosphere, facilitating the deposition of charged particles to Earth’s polar region, where the magnetic field converges, and interacts with oxygen and nitrogen atoms in the upper atmosphere. Such electrons accelerate towards the north and south poles and can generate intense radio emissions with frequencies around a few hundred kHz.

Yu’s team says the newly observed solar radio emissions, detected over an extensive sunspot region that forms temporarily where the magnetic fields on the Sun’s surface are particularly strong, differ from previously known solar radio noise storms – both spectrally and temporally.

“Our spatially, temporally and spatially resolved analysis suggests that they are due to the electron-cyclotron maser (ECM) emission, which involves energetic electrons trapped in converging magnetic field geometries,” Yu explains. “The cooler and intensely magnetic regions of sunspots provide a favorable environment for ECM emission, drawing parallels with the magnetic polar caps of planets and other stars and potentially providing a local solar analog to study these phenomena.”

“Unlike Earth’s auroras, however, these sunspot auroral emissions occur at frequencies ranging from hundreds of thousands of kHz to about 1 million kHz – a direct result of the sunspot’s magnetic field being thousands of times stronger than that of the soil.”

“Our observations show that these radio bursts are also not necessarily related to the timing of solar flares,” said Rohit Sharma, a scientist from the University of Applied Sciences Northwestern Switzerland (FHNW) and co-author of the study. “Instead, sporadic outburst activity in nearby active regions appears to pump energetic electrons into large-scale magnetic field loops anchored in the sunspot, which then drive the ECM radio emission over the region.”

The ‘sunspot radio aurora’ is thought to exhibit rotational modulation in sync with the sun’s rotation, creating what Yu describes as a ‘cosmic lighthouse effect’.

“As the sunspot crosses the solar disk, it creates a rotating beam of radio light, similar to the modulated radio aurora we observe from rotating stars,” Yu noted. “Since this sunspot radio aurora is the first detection of its kind, our next step involves a retrospective analysis. We want to determine whether some of the previously recorded solar outbursts could be examples of this newly identified emission.”

The Sun’s radio emissions, although fainter, are compared to stellar aurora emissions observed in the past and may indicate that starspots on cooler stars, like sunspots, could be the sources of certain radio bursts that are observed in various stellar environments.

‘This observation is one of the clearest evidence of radio ECM emissions we have seen from the Sun. The features resemble some of those observed on our planets and other distant stars, leading us to consider the possibility that this model could potentially be applicable to other stars. with starspots,” said Bin Chen, NJIT-CSTR associate professor of physics and co-author.

The team says the latest insight, which links the behavior of our Sun and the magnetic activities of other stars, could prompt astrophysicists to rethink their current models of stellar magnetic activity.

“We are beginning to solve the puzzle of how energetic particles and magnetic fields interact in a system with the presence of long-lived starspots, not only on our own Sun, but also on stars far beyond our solar system,” said NJIT Solar. researcher Surajit Mondal.

“Understanding these signals from our own Sun can help us better interpret the powerful emissions from the most common star type in the universe, M dwarfs, which can reveal fundamental connections in astrophysical phenomena,” said Dale Gary, professor of NJIT-CSTR . of physics.

The research team – including collaborators Marina Battaglia of FHNW and Tim Bastian of the National Radio Astronomy Observatory – used broadband dynamic radio imaging spectroscopy observations from the Karl G. Jansky Very Large Array to make the discovery.