what happens when a nebula expands
The outer layers begin to expand, cool and shine less brightly. The expanding star is now called a Red Giant. The star expands to a Red Giant, below. Stage 8 - The helium core runs out, and the outer layers drift of away from the core as a gaseous shell, this gas that surrounds the core is called a Planetary Nebula.A Planetary Nebula. (Below, NGC 6543).he outer layers begin to expand, cool and shine less brightly. The expanding star is now called a Red Giant. The star expands to a Red Giant, below. Stage 8 - The helium core runs out, and the outer layers drift of away from the core as a gaseous shell, this gas that surrounds the core is called a Planetary Nebula.