Planetary nebulae are some of the most beautiful objects in the universe.
They are formed when an intermediate mass star no longer has enough hydrogen to sustain nuclear fusion. The energy from nuclear fusion cannot counter gravitational forces and the star collapses. This causes the core of the star to heat up, and the outer shell of the star is ejected. The exposed core emits extraordinarily intense ultraviolet radiation which ionises the expelled shell, causing it to emit light - primarily at the wavelengths of hydrogen alpha and oxygen III.
Click on each image for more details.
They are formed when an intermediate mass star no longer has enough hydrogen to sustain nuclear fusion. The energy from nuclear fusion cannot counter gravitational forces and the star collapses. This causes the core of the star to heat up, and the outer shell of the star is ejected. The exposed core emits extraordinarily intense ultraviolet radiation which ionises the expelled shell, causing it to emit light - primarily at the wavelengths of hydrogen alpha and oxygen III.
Click on each image for more details.