According to the explanation given in the passage, which of the following causes superbubbles to gradually assume the shape of a chimney?
A.
The gravitational attraction of supernovas adjacent to the region of the chimney's formation
B.
The effect of entropy on the relative abundance of hot interior gas within the superbubble
C.
A chemical reaction involving ionized trace ions at the heart of the superbubble
D.
A tendency toward coalescence in the gases that contribute to the formation of the superbubble
E.
A natural buoyancy of the superbubble, which causes the chimney to stretch and become a gaseous conduit