(e) evolution of a massive star into a red super giant and then either a…

The idea

A massive star, meaning one with much more mass than the Sun, leaves the main sequence and expands into a red super giant. Its core continues fusing heavier nuclei until iron builds up, and fusion can no longer release net energy. The core then collapses rapidly, and the outer layers are blown away in a supernova explosion. What remains depends on the mass of the collapsed core: a neutron star forms if the remnant mass is below roughly three solar masses, while a black hole forms if it is greater. So the route is massive star, red super giant, supernova, then either neutron star or black hole.

What earns the marks

• A massive star evolves off the main sequence to become a red super giant.
• Core fusion proceeds to heavier elements until an iron core forms and fusion stops releasing net energy.
• The core collapses and the outer layers are ejected in a supernova.
• The final remnant is a neutron star or a black hole, depending on the mass of the collapsed core.

Common mistakes and how to put them right

• Thinking every star becomes a red super giant.

  Put it right: Only massive stars do, while lower-mass stars become red giants.

• Believing the supernova leaves only a black hole.

  Put it right: A neutron star is the more common remnant for many massive stars.

• Assuming the supernova creates the remnant from nothing.

  Put it right: The remnant is the collapsed core left behind after the outer layers are ejected.

Exam tips

• Learn the sequence as a chain: massive star, red super giant, supernova, neutron star or black hole.
• Link the final outcome to the mass of the remaining core, not to the original mass alone.
• Use the term supernova for the explosion and super red giant or red super giant for the expanded star, keeping the two ideas separate.