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[Sky Map]                         Cas A in Context
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[Chronological Listing]             [XRAY OF CAS A]  Cassiopeia A, or Cas A is the
[Photo Album Tutorial]                               remnant of a massive star that
[Key to Terms]                    exploded around three hundred years ago. The
[Search]                          material from the explosion is rushing outward at
                                  supersonic speeds in excess of two million miles
                                  per hour. As this matter crashes into gas that
             [LAUNCH]             surrounded the former star, shock waves analogous
                                  to awesome sonic booms heat the gas and heat the
                                  ejected matter to temperatures in excess of fifty
                                  million degrees. (pictured above left: Chandra's
                                  X-ray image of Cas A)

                                  The study of remnants of exploded stars, or
                                  supernovae, is essential for our understanding of
                                  the origin of life on Earth. The cloud of gas and
                                  dust that collapsed to form the sun, Earth and
                                  other planets was composed mostly of hydrogen and
                                  helium, with a small amount of heavier elements
                                  such as carbon, nitrogen, oxygen and iron. The
                                  only place where these and other heavy elements
                                  necessary for life are made, is deep in the
                                  interior of a massive star. There they remain
                                  until a catastrophic explosion spreads them
                                  throughout space.

                                  About every fifty years in our galaxy, a massive
                                  star explodes. The shell of matter thrown off by
                                  the supernova creates a bubble of multi-million
                                  degree gas called a supernova remnant. Cas A is a
                                  prime example. The hot gas will expand and
                                  produce X-rays for thousands of years.

                                  [Link to First Chandra Targets]
                                  Cas A in Context              Cas A Index
                                  Constellation                 More on Supernovae
                                  Cassiopeia                    Supernova Word
                                  Locate Cas A in the           Search
                                  Sky                   [Image] PKS 0637-752
                                  What Do the Images            Note on Cosmic
                                  Tell Us?                      Distances
                                  Cas A Fact Sheet
                                  (Press)

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                              Revised: 08/26/99