Planetary nebula (Artist's impression)

This artist's concept shows a 3D model of a planetary nebula. Planetary nebulae, despite their name, are nothing to do with planets. They are a phase that Sun-like stars go through when they run out of fuel. The outer layers of the star are puffed out, then heated up and ionised by the hot remnant of the star's core that remains in the centre. Their name comes from astronomers who observed these objects through early telescopes, which appeared to show roughly spherical objects reminiscent of the outer planets of the Solar System. High resolution observations with Hubble and other telescopes show their structure is in fact far less regular.