Overview
In a groundbreaking discovery, solar scientists have observed a mesmerising display of radio waves emanating from a sunspot, strikingly resembling the enchanting auroras or Northern Lights seen on Earth. This unprecedented observation marks the first-ever identification of an aurora signal caused by the acceleration of electrons through a sunspot on the Sun’s surface.
The Stellar Discovery-Aurora on the Sun
Situated approximately 25,000 miles (40,000 kilometres) above a shadowy and relatively cool expanse of the Sun, these intriguing “auroral” radio emissions have the potential to illuminate not just the dynamics of intense solar radio bursts but also shed light on sizable starspots outside our solar system.
The keen eyes behind this discovery belong to astronomers from the New Jersey Institute of Technology’s Center for Solar-Terrestrial Research (NJIT-CSTR).
Sijie Yu, the lead author of the research and a scientist at NJIT-CSTR, remarked in a statement that they had identified a distinctive form of enduring polarised radio bursts originating from a sunspot, lasting for more than a week. According to Yu, this contrasts with the usual transient solar radio bursts, which typically endure for only minutes or hours.
As per the team’s insights, the recently discovered sunspot radio emissions originate in regions where the Sun’s magnetic field lines exhibit heightened strength.
What sets these emissions apart is their origin and distinctiveness from the previously documented solar radio noise storms. The uniqueness lies in the spectrum, encompassing the range of wavelength categories they traverse and the extended duration of these wavelengths. The discovery is exciting and can potentially reshape the understanding of magnetic processes in stars.
What are Auroras?
Auroras, those dazzling displays of light in the night sky, are a natural phenomenon caused by the interaction between charged particles from the Sun and the Earth’s magnetic field.
When these charged particles collide with gases in the Earth’s atmosphere, such as oxygen and nitrogen, they emit light in various colours, creating the stunning visual spectacle we know as auroras.
They are called the aurora borealis or the Northern Lights.
What Exactly Causes the Colours in an Aurora?
Altitude and atomic interactions precede the specific hues that grace the cosmic canvas.
At higher altitudes, it was reported that a rare red glow emerges when ions collide with oxygen atoms. Meanwhile, the more commonly observed green-yellow auroras appear when ions interact with oxygen at lower altitudes.
The palette of colours extends further into the lower fringes of auroras, where reported observations indicate the presence of reddish and bluish lights, a magical outcome of ions encountering nitrogen atoms. For the discerning observer, there was also mention of a subtle play of blue and purple arising from the interaction between ions and hydrogen or helium atoms.
How are these sunspot auroras different from that of the conventional Earth auroras?
The sunspot auroras present a fascinating difference from their Earthly halves.
According to the team’s findings, these aurora-like phenomena emerge from the entrapment of high-energy electrons within converging solar magnetic fields. The cooler and intensely magnetic regions within sunspots create a conducive environment for the occurrence of electron-cyclotron maser (ECM) emissions, setting them apart from Earth’s auroras.
Unlike Earth’s auroras, the sunspot aurora emissions occur at frequencies ranging from hundreds of thousands of kHz to approximately 1 million kHz. This frequency range directly reflects the sunspot’s magnetic field, which is thousands of times stronger than Earth’s, as explained by lead researcher Sijie Yu.
Adding to the intrigue, the rotation of sunspot auroras synchronises with solar rotation, creating what Yu describes as a “cosmic lighthouse effect.” As the sunspot traverses the solar disk, it generates a rotating beam of radio light akin to the modulated radio auroras observed from rotating stars.
The team’s findings have been published in the journal Nature Astronomy.
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