What Is #30: A Supernova

In the 30th installment in this "What Is" series, I want to spend a few moments talking about supernovae, plural for supernova. A supernova is the final stage of a high mass star that has several times the mass of the Sun. These stars end their lives in a spectacular 'explosion'. I've put explosion in quotes because it really isn't an explosion as we think of an explosion.

This composite shows the Cassiopeia A supernova remnant across the spectrum: Gamma rays (magenta) from NASA's Fermi Gamma-ray Space Telescope; X-rays (blue, green) from NASA's Chandra X-ray Observatory; visible light (yellow) from the Hubble Space Telescope; infrared (red) from NASA's Spitzer Space Telescope; and radio (orange) from the Very Large Array near Socorro, N.M. Credit: NASA/DOE/Fermi LAT Collaboration, CXC/SAO/JPL-Caltech/Steward/O. Krause et al., and NRAO/AUI.

As a high mass star nears the end of its life, it begins to fuse more massive elements all the way up to iron in the core. Iron, the element with the greatest mass per nuclear particle, cannot be fused. At this point, fusion in the core stops and the core collapses very quickly until it reaches a point in which the neutrons cannot be packed in any tighter. The star doesn't have enough mass to break through neutron degeneracy. All of this material rushing in to the center hits this 'wall' and rebounds violently, creating what we call a supernova explosion. Unlike a bomb exploding, a supernova still has a leftover core, which we call a neutron star, an object I discussed in this series a while back.

If the star has even more mass, it could break through neutron degeneracy and leave behind a black hole, but this is only for the most massive of massive stars.

The supernova explosion creates many heavier elements beyond iron on the periodic table, but it doesn't appear as if a supernova has enough energy to create the heaviest elements. To create these elements, such as gold, even more energetic astronomical events are needed, to be discussed in a future post in this series.

A supernova releases a great amount of energy, so it is best to not be near one when it goes off. It is estimated that a supernova within 100 light years of us will greatly harm life on Earth by heating the atmosphere several degrees very quickly and wiping out a good chunk of the ozone layer. Not good for those of us who need this atmosphere to live! Fortunately we do not have any stars within 100 light years of us that show signs of reaching a supernova stage any time soon! Phew! There is some evidence, however, of past supernovae explosions linking to mass extinctions on Earth.