why Sun's outer layer is warmer than inner layer

A Queen’s University Belfast scientist has revealed the theory behind one of the most complex questions of the universe. ‘why the interior of the Sun is cooler than its outer surface?’ The magnetic waves of Sun strengthen and grow as they emerge from its surface, which could help to solve the mystery of how the corona of the Sun maintains its multi-million-degree temperatures.

For many years (approx 60) the observations of the Sun have shown that as the magnetic waves leave the interior of the Sun they grow in strength but until now scientists have no solid theory to prove this phenomenon.

The high temperatures at the corona have also always been a mystery. Normally as we see and feel the closer we are to a heat source, the warmer we feel. But in the case of Sun, it is reversed ‘on the Sun its outer layers are warmer than the heat source at its surface‘.

For a long time, it has been accepted by scientists that magnetic waves channel energy from the Sun’s vast interior energy reservoir, which is powered by nuclear fusion, up into the outer regions of its atmosphere. Therefore, understanding how the wave motion is generated and spread throughout the Sun is of huge importance to researchers.

The team of 13 scientists led by Queen’s University, was spanned in five countries and 11 research institutes including the University of Exeter; Northumbria University; the European Space Agency; Instituto de Astrofísica de Canarias, Spain; University of Oslo, Norway; the Italian Space Agency and California State University Northridge, USA.

60-year-old mystery of Sun’s magnetic wave

In the experiment the researchers formed a consortium called “Waves in the Lower Solar Atmosphere (WaLSA)” and used advanced high-resolution observations from the National Science Foundation’s Dunn Solar Telescope, New Mexico, to study the waves.

“This new understanding of wave motion may help scientists uncover the missing piece in the puzzle of why the outer layers of the Sun are hotter than its surface, despite being further from the heat source, said: head of the experts Dr. David Jess from the School of Mathematics and Physics at Queen’s.

“By breaking the Sun’s light up into its basic colours, we were able to examine the behaviour of certain elements from the periodic table within its atmosphere, including silicon (formed close to the Sun’s surface), calcium and helium (formed in the chromosphere where the wave amplification is most apparent).

“The variations in the elements allowed the speeds of the Sun’s plasma to be uncovered. The timescales over which they evolve were benchmarked, which allowed the wave frequencies of the Sun to be recorded. This is similar to how a complex musical ensemble is deconstructed into basic notes and frequencies by visualising its musical score.”

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By analyzing the data collected in the experiment they found that the wave amplification process can be attributed to the formation of an ‘acoustic resonator’, where significant changes in temperature between the surface of the Sun and its outer corona create boundaries that are partially reflective and act to trap the waves, allowing them to intensify and dramatically grow in strength.

The scientists also found that the thickness of the resonance cavity –the distance between the significant temperature changes — is one of the main factors governing the characteristics of the detected wave motion.

“The effect that we have found through the research is similar to how an acoustic guitar changes the sound it emits through the shape of its hollow body. If we think of this analogy we can see how the waves captured in the Sun can grow and change as they exit its surface and move towards the outer layers and exterior” said, Dr Jess one of the team members.

“This new research opens the door to providing a new understanding of the mystery surrounding the Sun’s magnetic waves. This is a crucial step towards explaining the coronal heating problem — where the temperature a few thousand km from the surface — is hotter than the heat source itself,” said, Dr. Ben Snow, from the University of Exeter and a co-author of the study.

The research is published in Nature Astronomy. If you wish to study more you can go to the given link and download the complete paper. the research was funded by the Science and Technology Facilities Council, Randox Laboratories Ltd., Ministerio de Economía y Competitividad, Invest Northern Ireland, the Department for Employment and Learning in Northern Ireland, EC | Horizon 2020 Framework Programme and Norges Forskningsråd.

After the success of this experiment now the global physics community is planning to make further investigations using the newest-generation solar telescopes that will become available over the next few years. This includes the upcoming Daniel K. Inouye Solar Telescope, a $300 million observatory which is currently in Hawaii.


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