Mysterious aurora-like radio emissions emanate from sunspots

Seeing the aurora borealis on Earth is quite rare at our latitudes, but how about seeing it on the Sun? Scientists from the New Jersey Institute of Technology (NJIT) have discovered an unprecedented solar phenomenon. They managed to detect radio emissions emanating from spots on the Sun’s surface. About a discovery that can change the view of some astronomical knowledge, reports the website StudyFinds.

The researchers say the new radio emission shares characteristics with the aurora radio emission commonly observed in planetary magnetospheres such as those around Earth, Jupiter and Saturn, as well as some low-mass stars.

Northern Lights on the Sun?

“We recorded a special type of long-lasting polarized radio bursts emanating from a sunspotwhich persist for more than a week,” says lead study author Sijie Yu in a press release. “This is quite different from the usual transient solar radio flares, which usually last for a few minutes or hours. This is an exciting discovery that has the potential to change our understanding of stellar magnetic processes.”

Sunspots are relatively dark and cool regions on the Sun’s surface that have long been the subject of scientific interest. In this study, scientists at NJIT’s Center for Solar and Terrestrial Research detailed radio observations of a peculiar aurora-like display that occurs 40,000 kilometers above the sunspot.

To understand the significance of this discovery, it is necessary to understand parallels with the terrestrial aurora borealis, such as the Northern Lights (Aurora Borealis) and the Southern Lights (Aurora Australis). These breathtaking light shows are created when solar activity disrupts the Earth’s magnetosphere, leading to the precipitation of charged particles into the polar regions of our planet.

These particles then interact with oxygen and nitrogen atoms in the upper layers of the atmosphere and create intense radio radiation at frequencies of several hundred kHz. In the case of the Sun, similar processes appear to be taking place above sunspots.

It’s a little different on the Sun

A unique aspect of this discovery is that radio emissions from sunspots differ from previously known solar radio noise storms, both in terms of spectral characteristics and duration. Scientists believe these emissions are related to something called “electron-cyclotron maser (ECM) emission” and involve energetic electrons trapped in regions of strong magnetic field. Sunspots, which are cooler and intensely magnetic regions on the Sun, provide an ideal environment for emitting ECM – they can thus be compared to magnetic polar caps on planets and stars.

“Our time- and space-resolved analysis suggests that they are caused by electron-cyclotron maser (ECM) emission, involving energetic electrons trapped in converging magnetic field geometries,” explains Yu. “The cooler and intensely magnetic regions of sunspots provide a favorable environment for ECM emission to occur, leading to parallels with the magnetic polar caps of planets and other stars and potentially providing a local solar analogy for the occurrence of these phenomena.”

Interestingly, unlike terrestrial auroras, which emit radio waves at lower frequencies, solar auroras occur at much higher frequencies – from hundreds of thousands to roughly 1 million kHz – which is due to the fact that the Sun’s magnetic field is thousands of times stronger than the Earth’s magnetic field.

The study also challenges the traditional view that these radio flashes are related to solar flares, as sporadic eruptive activity in nearby active regions appears to drive energetic electrons into the magnetic field loops anchored in the sunspot, driving the radio emission above the region. As a sunspot moves across the sun’s disk, it creates a rotating beam of radio light, leading to the “cosmic beacon effect”.

Possible source of radio flashes

The discovery of these solar radio emissions, which are however weaker than terrestrial auroras, is similar to stellar aurora emissions observed in the past. This suggests that starspots on cooler stars, similar to sunspots on our Sun, may be the source of some radio flashes observed in different stellar environments.

The implications of this finding are far-reaching, as it links the behavior of our Sun to the magnetic activity of other stars. This connection could prompt astrophysicists to reevaluate their current models of stellar magnetic activity, leading to a better understanding of phenomena occurring in stars outside our solar system.

The research team, which included scientists from institutions such as the University of Glasgow and the National Radio Astronomy Observatory, used advanced radio imaging spectroscopy observations from Karl Guthe Janske’s Very Large Array. The results of the research were published on Monday, November 13 in the scientific journal Nature Astronomy.