The stellar corona in the outermost layer of the Sun’s atmosphere is immensely hotter than the star’s surface, often reaching temperatures thousands of times higher, possibly due to weak but stable propagating waves that facilitate energy transfer.
The solar corona is the outermost layer of the Sun’s atmosphere. Photo: Popular Science
The stellar corona, located in the outermost layer of a star’s atmosphere, is immensely hotter than the star’s surface, often reaching temperatures of up to 40 million degrees Celsius, as reported by NASA. This region, known as the corona, consists of ionized and superheated gas called plasma and is the origin of extreme space weather events such as solar flares. However, the reason behind the corona’s extreme heat had long puzzled researchers.
In a detailed study published on September 12th in the journal Nature Communications, scientists investigated a common phenomenon associated with stars known as low-amplitude torsional Alfvénic fluctuations. These are fluctuations within the stellar corona’s magnetic field, a vaulted structure made of plasma that starts in the photosphere and extends to the corona. These waves are relatively weak but maintain their strength over multiple oscillation cycles. Therefore, they can supply a significant amount of energy to the corona over time.
The research team focused on how these waves propagate vertically, horizontally, or at any angle, a characteristic known as polarization. The ability to analyze the 3D geometric features of these waves could reveal their origin and the energy they carry. However, scientists previously lacked a method to observe these waves from multiple perspectives, which was necessary to detect polarization.
Valery Nakariakov, a stellar physicist at the University of Warwick in Coventry, UK, and colleagues used data from the European Space Agency’s Solar Orbiter and NASA’s Solar Dynamics Observatory to analyze the stellar corona from various vantage points. They discovered that nearly all the waves vibrated in the same direction. This finding suggests that energy from the star’s surface can propagate to the corona, heating it. According to Nakariakov, the research results provide crucial insights into the long-standing question of what heats a star’s corona.