Researchers Discover Aurora-Like Radio Signals Emanating Above a Sunspot

According to researchers, the distinctive radio emission exhibits similarities with the auroral radio emissions frequently observed in planetary magnetospheres, including those encircling Earth, Jupiter, and Saturn, as well as in specific low-mass stars.

This finding provides fresh perspectives on the source of intense solar radio bursts, potentially paving the way for a deeper comprehension of analogous phenomena in distant stars characterized by substantial starspots. Sijie Yu, the lead author and scientist at NJIT-CSTR, emphasizes the significance of these insights.

Yu highlights the identification of an unusual form of prolonged polarized radio bursts originating from a sunspot, lasting for over a week. This contrasts with the usual transient solar radio bursts, which typically endure only minutes or hours. The discovery presents an exciting prospect with the potential to reshape our understanding of magnetic processes occurring in stars.

Renowned auroral light displays, such as the Northern Lights (Aurora Borealis) and Southern Lights (Aurora Australis), illuminate Earth’s polar regions when solar activities disrupt the magnetosphere. This disturbance enables the precipitation of charged particles to Earth’s polar areas where the magnetic field converges, leading to interactions with oxygen and nitrogen atoms in the upper atmosphere. As electrons accelerate toward the north and south poles, they produce powerful radio emissions at frequencies typically around a few hundred kHz.

The team led by Yu notes that the recently identified solar radio emissions, observed above an extensive sunspot region that temporarily emerges where the sun’s surface magnetic fields are exceptionally robust, exhibit distinctions from previously recognized solar radio noise storms in both spectral and temporal aspects.

According to Yu, the team’s in-depth analysis, considering spatial, temporal, and spectral aspects, indicates that these emissions result from the electron-cyclotron maser (ECM) process. This mechanism involves energetic electrons confined within converging magnetic field configurations. Sunspots, characterized by cooler temperatures and strong magnetic fields, create an optimal setting for the occurrence of ECM emission. This draws parallels with magnetic polar caps observed on planets and other stars, presenting a potential local solar analog for the study of these phenomena.

Yu notes that in contrast to Earth’s auroras, the aurora emissions from sunspots manifest at frequencies ranging from hundreds of thousands of kHz to approximately 1 million kHz. This characteristic stems directly from the sunspot’s magnetic field, which is thousands of times more potent than Earth’s. Furthermore, Sharma, a co-author of the study from the University of Applied Sciences Northwestern Switzerland (FHNW), points out that these radio bursts are not necessarily synchronized with the occurrence of solar flares. Instead, sporadic flare activity in nearby active regions appears to inject energetic electrons into large-scale magnetic field loops connected to the sunspot, subsequently fueling the electron-cyclotron maser (ECM) radio emissions observed above the region.

The phenomenon known as the “Sunspot radio aurora” is believed to showcase rotational modulation synchronized with the solar rotation. This creates what Yu refers to as a “Cosmic lighthouse effect.”

Yu explains that as the sunspot moves across the solar disk, it generates a rotating beam of radio light, akin to the modulated radio aurora observed from rotating stars. Describing this as the first detection of its kind, the next step involves retrospective analysis to ascertain whether some of the previously recorded solar bursts could be instances of this newly identified emission.

While the solar radio emissions are comparatively fainter, they draw comparisons to previously observed stellar auroral emissions. This similarity raises the possibility that starspots on cooler stars, analogous to sunspots, might serve as sources for specific radio bursts detected in diverse stellar environments.

Bin Chen, an associate professor of physics at NJIT-CSTR and a co-author of the study, emphasizes that this observation provides exceptionally clear evidence of radio electron-cyclotron maser (ECM) emissions from the sun. The identified characteristics bear resemblance to those observed on planets within our solar system and other distant stars. Chen suggests that this model could potentially be applicable to other stars hosting starspots, broadening our understanding of similar phenomena beyond our solar system.

The team suggests that the recent revelation, connecting the behavior of our sun with the magnetic activities of other stars, may prompt astrophysicists to reconsider their existing models of stellar magnetic activity.

Surajit Mondal, a solar researcher at NJIT, emphasizes that the emerging understanding is gradually assembling the puzzle of the interplay between energetic particles and magnetic fields in a system featuring persistent starspots. This insight extends beyond our solar system, encompassing not only our sun but also stars situated far beyond.

Dale Gary, a distinguished professor of physics at NJIT-CSTR, underscores the significance of comprehending signals from our sun. This understanding enhances the interpretation of potent emissions from the most prevalent star type in the universe, M-dwarfs. The insights gained from studying these emissions may unveil fundamental connections in various astrophysical phenomena.

The research team, which included collaborators Marina Battaglia from FHNW and Tim Bastian from the National Radio Astronomy Observatory, employed broadband dynamic radio imaging spectroscopy observations from the Karl G. Jansky Very Large Array to make this significant discovery.

Resources

1. ^NEWSPAPER Jenkins, J. & New Jersey Institute of Technology. (2023, November 13). Scientists uncover aurora-like radio emission above a sunspot. Phys.org. [Phys.org]
2. ^JOURNAL Yu, S., Chen, B., Sharma, R., et al. (2023). Detection of long-lasting aurora-like radio emission above a sunspot. Nature Astronomy. [Nature Astronomy]