New Delhi: The changing structure of the magnetic field on the Sun's surface determines whether the Sun emits a solar flare or a Coronal Mass Ejection (CME), Indian astronomers have found. They believe this understanding will be useful in improving solar weather predictions.
A solar flare is an intense burst of radiation that comes from the release of magnetic energy linked with certain regions on the Sun, while CMEs are large expulsions of plasma and magnetic fields from the Sun's corona.
Regions on the Sun with disturbed magnetic fields or active regions, which sometimes exhibit solar flares only and no CMEs, were explored by the astronomers.
Solar weather can affect electrical and communication systems on Earth and satellite systems in space, and the fact that disturbed magnetic field regions on the Sun can help determine whether the star will emit a solar flare or CME is of utmost importance.
The study was conducted by a team of scientists from the Indian Institute of Astrophysics, Bengaluru. The results were recently published in the Monthly Notices of the Royal Astronomical Society journal.
Sun's Magnetic Field And Solar Weather Predictions
The Sun harbours hot plasma which moves around in the star's magnetic field. The magnetic field, near the surface of the Sun, and the hot plasma are connected to each other. The regions on the Sun's surface, where eruptions of the magnetic field may occur in loops are known as Active Regions.
The magnetic field is complex because it may become twisted, realign its geometry and release massive amounts of energy. Before the release, the energy is stored as magnetic energy. Light is emitted in many wavebands during this process, and this emission is called a solar flare.
When a huge amount of hot gas, with its embedded magnetic field, is ejected at high velocities into the solar corona, the phenomenon is called a CME.
Active Regions may produce either solar flares, or CMEs, and sometimes, both. The new study explains that the magnetic field of the Sun's active regions determines what will be emitted.
Study Can Help Understand Magnetic Field Production In Stars, Planets
The changing configuration of the magnetic field on the Sun is quantified by magnetic helicity, a measure of twist and shear of magnetic field. The twisted magnetic fields store energy. Magnetic helicity may be injected into the corona of the active region of the Sun, when the magnetic field is twisted.
The Sun removes excess helicity or twists in the magnetic field through CMEs when the magnetic helicity crosses a threshold value, the study found. In other words, when the Sun's magnetic field exhibits excessive twists, the Sun ejects huge amounts of gases at high velocities to get rid of the helicity. However, it is challenging to find the threshold value of coronal velocity.
Dr. Vemareddy spotted a peculiar evolution of helicity injection in the Active Region called AR 12257, which is devoid of CMEs.
NASA's Solar Dynamics Observatory in space takes magnetic and coronal images of the Sun every 12 minutes. The peculiar event in AR 12257 was studied using these images taken by NASA's Observatory.
The scientists observed that for the first two and a half days, the active region injected positive helicity. However, this was followed by negative helicity. Thus, the active regions where the sign of helicity reverses with time cannot produce coronal mass ejection, the study found. In other words, CMEs are not produced by the active regions in which the value of helicity becomes negative as time progresses.
A statement issued by the Ministry of Science and Technology, India, said studies of the injection of helicity help improve predictions of the eruptive potential of an active region, according to the IIA team. Also, the magnetic field production in stars and planets can also be understood with the help of these results.