The Ring Nebula (M57) Imaged by John Catlyn

M57 is a planetary nebula in the constellation of Lyra and is visible in small telescopes. 

Planetary nebulae such as M57 are formed when a low or medium mass star (such as the Sun) exhaust its hydrogen in the stellar core.   The structure of the star changes so it can achieve a new equilibrium condition in which it can continue to burn heavier elements.   When the supply of hydrogen at the core is exhausted, radiative energy is unable to support the weight of the star above it and it begins to collapse, converting gravitational energy into thermal energy.  As the star collapses and the temperature of the core rises, the fusion of Hydrogen into Helium occurs in the shell.  When the core temperature reaches about 100 million degress fusion of Helium into Carbon begins. As the core contracts, the outer regions of the star begin to expand and the star becomes a red giant. A strong wind begins to blow from the star’s surface and, in the course of the star’s red giant life, carries away most of the hydrogen envelope surrounding the star’s central core.  The envelope of ejected matter becomes a planetary nebula.

Illuminated by their central stars Planetary nebulae can display beautiful structures: some are spherical or helical, others have bipolar shapes, and others are rather irregularly shaped. Within a few tens of thousands of years the matter forming a planetary nebula will intermingle with the interstellar medium and disperse.

More massive stars will meet a far more cataclysmic end – a supernova.

Lookup M57 on SEDS