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X-ray the sun and we might find it full of holes. Coronal holes, that is. The corona is the ring of light, or halo, around the sun. In historical x-rays the corona appears uneven and now we may understand why.
The corona is brightest near sun spots and darkest near coronal holes. The sunspots prevent the outflow of solar wind which carries energy away from the sun and helps cool the massive ball of burning fire. The coronal holes, however, allow solar wind to escape deep into space.
In the 1970s, Skylab showed the significance of the coronal holes. Approximately every 27 days there are fast jet streams in the solar wind and magnetic storms. These phenomena correspond with the coronal hole cycle, when the sunspot cycle is at its minimum.
To keep the glowing ball of fire from getting too hot, the two poles of the sun have permanent coronal holes, allow solar wind plasma to exit freely.
Image courtesy of NOAA.