Star Death

Demonstrate an understanding that planetary nebulae and supernovae are associated with the death of stars

Eventually the star burns up the hydrogen in its core and burns the hydrogen in its outer core or shell.

It becomes brighter and expands to a red giant. Helium is now being burnt by the star.

At this point different scenarios present themselves depending on the mass of the star.

If the star has a very small mass it shrinks to a red dwarf, burning its hydrogen and helium.

If a star, such as our Sun, has under 4 solar masses it will grow to a red giant and eventually puff away its outer layers before shrinking to a white dwarf, of under 1.5 solar masses.

If the star has between 4 and 25 solar masses it will grow to a red super giant and explode as a supernova, leaving a neutron star the size of Earth.

If it has over 25 solar masses it will again explode as a supernova but will produce a black hole.


Planetary Nebula is a misleading name. Originally they were thought to be a region around a star where planets would form. This is not the case, quite the opposite in fact.

When a red giant expels its outer layers before becoming a white dwarf or neutron star, the layers become a thin sheet of gas around the remains.

Their shape and colour depend on the size, composition of the Sun and its direction to us from Earth. Planetary Nebula can range from the width of the Solar System to more than a light year wide.

There are many good examples of planetary nebulae, some are beautiful, some are eerie and some are quite funny such as the Clownface Nebula in Gemini.

Supernova remnants are similar to planetary nebulae only caused by a supernova and usually more cataclysmic in appearance.


A supernova is the brightest event in space. There are two types of supernova:

  • 1 Similar to a nova where a dwarf takes material from a giant. This time the explosion destroys the dwarf. Typically this takes place when the mass of the white dwarf is over 1.4 solar masses.
  • 2 When a star has a mass greater than 8 solar masses. The red giant swells so much it collapses in on itself. These are dramatic events as once they explode the core forms a neutron star or a black hole.

The light curve shows a drastic increase in brightness before receding to a small luminance after a few months.

A planetary nebula is usually seen in the region of a supernova for years, sometimes centuries afterwards.

Supernovae is the plural of supernova.



Planetary Nebula Gallery New Window

Supernova Remnant Gallery New Window

Links New Window

How Stuff Works

Death of a star

Astronomy Picture of the Day Planetary Nebulae

Catching the Light Top Ten Planetary Nebulae


  • Describe the death of a star.
  • What are planetary nebula?
  • What is a supernova?