Supernova: A star's encore in the universe
By Amanda Jermyn



About every second, somewhere in the known universe a star explodes. Even though such stellar explosions emit huge amounts of light and other radiation, most go unnoticed here on earth because the universe is a pretty big place. Every now and then, however, an exceedingly bright light suddenly appears in the night sky where none was visible a few hours before. What we are witnessing is a supernova, the violent explosion of a star that has reached the end of its life. A supernova can briefly outshine an entire galaxy before fading over several weeks or months, and can radiate more energy than our sun will over its entire lifetime. The first recorded supernova was viewed with the unaided eye by Chinese astronomers in 185 AD, long before telescopes were invented. On average a supernova occurs about once every fifty years in a galaxy the size of our Milky Way. However, not every star will become a supernova. Our sun, for instance, does not have enough mass. Once it runs out of nuclear fuel it will expand into a red giant that will most likely vaporize earth, then gradually cool to become a white dwarf, but not to worry, that wonít happen until a couple of billion years from now.
For a star to explode as a supernova, it must have a mass of over eight times that of our sun. Nuclear fusion, the process powering all stars, exerts an outward pressure that holds a star up against its own gravity. However, the elements being fused become heavier as the star runs out of fuel, and the core becomes hotter and denser. Once it exceeds a certain mass, known as the Chandrasekhar limit, the pressure can no longer hold the star up, and it undergoes a gravitational collapse inward, releasing energy that heats and ejects the starís outer layers. This creates the brilliant blaze of light that characterizes a supernova. What remains after the collapse is a super-dense object called a neutron star, or else a black hole. Another type of supernova may be formed when a white dwarf starís gravity causes it to accumulate gas from a companion star orbiting it. The white dwarf eventually becomes so compressed that a runaway nuclear reaction occurs within it, resulting in a supernova explosion. It has recently been discovered that before exploding, supernovae vibrate and emit an audible hum. Because certain types of supernovae are known to blaze with equal brightness, they can be used to judge the distance of objects in space. Supernovae also play a major role in creating elements with masses higher than that of iron, and in triggering the formation of new stars. Some of the elements that make up our bodies were forged in supernovae. As Joni Mitchell sang in Woodstock, we are indeed ďstardust.Ē
The next Stars over Springfield will be held at the Springfield Science Museum on Friday, January 8th at 7.30pm. Astronomy educator Paul Cardone will speak on Spaceflight in the First Decade of the 21st Century. Afterwards the museumís 20-inch rooftop telescope will be opened to the public. In case of clouds a planetarium show will be presented instead.

Amanda Jermyn, of Longmeadow, has been a member of the Springfield Stars Club since 2000 and currently serves on the club's board of directors. For more information, visit the Springfield Stars Club Web site at www.reflector.org or call 1(800)336-9054.