Curated by RSF Research Staff
Puzzling Gamma-Rays from the Sun
Gamma-rays have been observed emanating from the solar poles at a higher rate than expected.
Gamma-rays are the highest observed energy of electromagnetic radiation and are typically produced in energy transitions in atomic nuclei. Similar to photons of light being emitted as electrons reconfigure in atoms, photons of light are released in the reconfiguration of nuclei in an atomic nucleus, albeit at a much higher energy range!
Our star – the Sun – is a hot rotating ball of plasma continuously emitting radiation at a broad range of energies, from radio to gamma-rays.
Energy generation is greatest in the centre of the Sun, decreasing radially outward.
High energy radiation, such as gamma-rays, are thus thought to be due to the bombardment of the solar atmosphere by high velocity protons - hadronic cosmic rays. However, as the gamma-rays from such an interaction are assumed to be absorbed long before they reach the solar surface – photosphere – the expected flux is not great and does not agree with observations. Fortunately, back in the 90’s the physicist Professor David Seckel and his colleagues showed that in some cases the solar atmospheric magnetic field can re-direct some of the cosmic rays, from ingoing to outgoing, before the interaction takes place. The resulting gamma-rays are thus directed outward and the efficiency is greatly enhanced.
Problem solved – well at least it was until recent measurements showed otherwise.
Utilizing the Fermi Gamma-Ray Space Telescope’s Large Area Telescope, Tim Linden and his colleagues have been observing the solar disk for the last 10 years. However, their recent analysis shows a steady flux of gamma-rays in the tens of GeV – that’s 10 billion electron volts. This significantly exceeds the amount predicted by the current model of gamma-ray production in the solar photosphere, leaving theorists perplexed.
The scientists are hopeful that the continued observations through the solar cycles will reveal a broader spectrum of energies up to the TeVs – a trillion electron volts - and hopefully help us to understand more about the nature of the solar gamma-ray emission and in particular the polar activity.
Amira Val Baker