Tranquil is a region within the Vesania Universe.
Tranquil is a seemingly stable region, 1 million light years across, in the centre of Vesania.
It appears like normal space, with many stars and planets. At its centre is the Serenus Galaxy, which is an attractive blue barred spiral.
Many planets are habitable.
In Tranquil, no energy is lost from the system. Energy blasted at by the stars is fed back into them, and heavy elements reconverted to hydrogen, so they never age or die. As such, there are no white dwarves, neutron stars, or black holes.
The planets do not lose heat or atmosphere to space permanently, it too is looped around.