Final answer:
A loop of gas following the magnetic field lines around sunspots' poles is called a prominence, which is a large, relatively cool structure suspended in the hot solar corona.
Step-by-step explanation:
A loop of gas following the magnetic field lines around sunspots' poles is known as a prominence. Prominences are huge clouds of relatively cool, dense gas suspended in the much hotter corona. They are visible in extreme ultraviolet light and can appear as glowing loops extending from the surface of the Sun. Unlike solar flares, which are sudden and intense bursts of radiation, or coronal mass ejections (CMEs), which are large expulsions of plasma and magnetic fields into space, prominences are more stable and less violent features of the Sun's atmosphere. Granulation refers to the rice-grain-like texture of the solar photosphere and is not related to the loop of gas in question.