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the hot atmosphere of the Sun [Q&A]


Vigneshwar of Poornaprajna College asks, how is it that the atmosphere of the Sun is hundreds of times hotter than the surface? Doesn’t nuclear fusion happen in the center?

Indeed, the corona of the Sun is at many millions of degrees, compared to the surface, which is at 5800 K. This is not due to nuclear fusion (which actually requires billions of degrees and very high pressures) except indirectly, since everything the Sun puts out can ultimately be traced back to this source.

Here is what the corona looks like when one looks in the extreme UV, at plasma that is at a million degrees K. This is an image from the 171Å filter band of the SDO/AIA telescope, which shows a remarkable spatial organization in loop like structures all over the Sun, and a zoomed in version at right.

The loop-like structures give a clue as to what is the controlling characteristic of the corona. These structures trace out magnetic field lines. The corona is threaded by intense magnetic fields, which are constantly jiggled around due to convective motions near the surface. This jiggling twists them up and introduces high stress into the fields, which often explosively rearrange themselves and release the excess energy as flares. This type of magnetic reconnections is one of the main causes of the high temperature in the corona. This is by no means an established picture, and is the subject of active research. There are other sources of heat input into the corona, waves propagating up and dissipating, or hot material shooting out as jets, that could contribute substantially to the energy budget.

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  1. Gurukula › solar differential rotation [project] on Tuesday, March 15, 2011 at 2:09 pm

    […] ranging from visible light photospheric images to magnetic maps to high-energy X-ray images of the corona. You can look up what the Sun looked like on any day going back […]