Dark places on the sun is appears,

Dark places or hole in the sun,

Footage captured by the Solar Dynamics Observatory shows parts of the corona where the particles leave the sun, causing the glow to be much dimmer, so the coronal hole looks dark. What are the cause are? Is sun going down to cool or solar is causing this black spots in the sun. Some experts says that it is the hole in the sun which is horrible for sun and solar system,