A granule is a cellular feature found on the surface of the sun that is caused by convection currents. Granules are situated atop convection cells, except in areas enveloped by sunspots, that release hot fluid from their interior. This process creates bright spots on the surface that sink inward.
Granules are around 1,000 kilometers across and only last for an average of 20 minutes before getting pushed aside by newly developing granules. This process results in the constant evolution of the sun's granulation pattern. The movement within granules can achieve supersonic speeds as high as 15,000 miles per hour, which creates sonic booms on the sun's exterior.