The dark area across the top of the sun in this image is a coronal hole, a region on the sun where the magnetic field is open to interplanetary space.

Source: NASA

https://cdn.nostrcheck.me/7f3daed3bff80cc2e502048eee688a0fa714b4b8a4f006392a46e5300b39e832/a143dd784abd17dff78f24859d116acdf6672a0ad5520f4f6b238edfe921060a.webp