The sun

The sun of Realmspace was and enourmous sphere of fire at the center of that crystal sphere, and the source of light and heat of the eight planets circling around it. In fact, the sun was so hot that any closer inspection was impossible for creatures not naturally immune to fire, even if magical aid was employed.

Features
The sun's surface was made up of varying areas of molten earth and fluid flame, a distinction which only was useful for its fire-loving inhabitants. Some areas called sunspots were somewhat cooler than its surroundings and could be recognized by their darker color. At other places pillars and loops of flame could violently spurt outward from the sun's surface for millions of miles.

The surface also features hundreds of portals to the Elemental Plane of Fire, allowing access to the natives of that place.

Another dreaded feature can be found 40 million miles away from the sun: Like balls on the spokes of a wheel, twelve spherical dead-magic zones with a diameter of 100,000 miles each orbit Realmspace's central body. They are called the sargassos and feared on every spelljammer, which depend on magic for movement after all.

Inhabitants
The sun was inhabited by many creatures originally native to the Elemental Plane of Fire: Efreet, firenewts, fire minons, helians, lavaworms and salamanders had been recognized. It has also been surmised that inhabitants of other fiery places on the planes made their home there.

Only a few attempts of the sun's denizens to leave their home have been registered. But any spelljamming ship that got close to the sun was violently attacked by them, especially the helians.

History
The wildspace of the Realmspace crystal sphere is unusually warm compared to others. This led sages to speculate that the sun and Realmspace itself were the oldest among the generally known crystal spheres.

Portfolio
Among the deities, Amaunator took responsibility for the sun within the Faerûnian pantheon, first Re then Horus-Re in the Mulhorandi and Utu within the Untheric pantheon.