Astonomers estimate that a supernova explosion occurs in a galaxy like the Milky Way every 30 to 50 years. Each of these events eventually deposits about 1044 joules of energyinto the interstellar gas that fills the galaxy. This is equivalent to the energy output of the Sun over its entire lifetime. In addition to energy, the ejected matter carries heavy elements such as iron which are formed by nuclear reactions during the explosion. In fact supernovae are probably the only source of many heavy elements.

Key Figures in Galactic History Because of chemical element enrichment and the fact that the characteristic interactions are so violent, supernova remnants are believed to play a major role in determining the history of galaxies. A good example is their influence on the formation of new stars and planets. The existence of the Earth itself was made possible only because the matter that formed our solar system had come, in part, from supernova explosions among earlier generations of stars. Supernova remnants are also thought to be the primary source of so-called cosmic radiation-a diffuse gas of extremely high energy, charged particles that bombards the earth from outside the solar system. For the above reasons, astronomers consider it important to understand the dynamic interactions between supernova remnants and their environments. There are now nearly 200 supernova remnants recognized in the Milky Way galaxy, with ages estimated to range from a few hundred years to tens of thousands of years. They are seen primarily as strong X-ray radiation emitted by the hot gas they contain and through "nonthermal" radio emissions produced by the cosmic radiation and strong magnetic fields somehow generated within them. Some are also spotted through visible light observations, but interstellar matter is very dusty, so most of the galaxy is too obscured to let their visible light reach us. "Key Figures in Galactice History" continued

Gas velocity vectors superimposed on gas density contours for a simulated supernova explosion on the edge of a giant interstellar molecular gas cloud. Results are shown at three times (100 years, 300 years and 650 years), demonstrating that long before the supernova remnant is clearly distorted in shape the gas motions inside it have responded to the higher density of the giant cloud.

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Supernova Remnants

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