In a first, Indian scientists measure Sun’s magnetic field

New Delhi: Indian scientists with international collaborators have measured the magnetic field of an eruption from the Sun’s atmosphere by observing the weak thermal radio emission associated with the erupted plasma for the first time. This offered a rare peek into the interiors of the Sun. The study of the phenomenon happening in the Sun’s atmosphere or the solar corona provides insights into the inner workings of the Sun.
A team of scientists from the Indian Institute of Astrophysics (IIA), an autonomous institute of the Department of Science & Technology (DST), Government of India, along with their collaborators, used data from their radio telescopes to measure the magnetic field and other physical conditions of the plasma in a CME detected on May 1, 2016. It was found with the help of radio telescopes of IIA in Gauribidanur, Karnataka, along with some space-based telescopes that observed the Sun in extreme ultraviolet and white light and was caught when the base of its activity was just behind the visible limb of the Sun.

This allowed the researchers to detect a much weaker radio emission called thermal or blackbody radiation from the plume of gas that was ejected in the CME. They were also able to measure the polarisation of this emission, which is indicative of the direction in which the electric and magnetic components of the waves oscillate. Using this data, they then calculated the physical properties of the ejected plasma as well. The results of the study by R. Ramesh, A Kumari, C Kathiravan, D Ketaki, and T J. Wang have been published in the leading international journal Geophysical Research Letters.

“Though CMEs can occur anywhere on the Sun, it is primarily those which originate from regions near the centre of the visible solar surface (called the photosphere) like the one we studied that are important for us, since they may propagate directly towards the Earth,” said R. Ramesh, Professor at the Indian Institute of Astrophysics (IIA) Bangalore and the lead author of the paper. “These CMEs are usually studied in visible light, but because the disc of the Sun is so much brighter, we can detect and follow these CMEs only when they have travelled beyond the Sun’s surface. However, radio observations of the thermal emission, like in our study, lets us study the CMEs right from the surface itself,” A Kumari, a co-author said.

“Knowing the source region of the CMEs, the associated magnetic field and their kinematics in the region up to seven lakh kms either above the solar surface or off its limb, are important to fully understand the characteristics of the CMEs in a holistic manner,” says C Kathiravan, another co-author of the study.

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